Assaying Gold and Silver

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Gold and Silver Mines O = Gold, + = Silver

When someone discovers a valuable mineral, pretty soon they need to know what the area is worth.
Should they spend a lot of time and money developing the property, or will it cost more than can be produced?

These questions opened Assay Offices all over the west with each new discovery of more Gold and Silver mines.


Assay Certificate

What is assaying and how do you go about doing it?
NOTE: If you are serious about this subject you may want to study:
Notes on assaying and assay schemes -1876.
Lab instructions - 1913
Or join 911 Metallurgist.


Old Assay Office

The art of assaying is a branch of analytical chemistry in connection with mining and metallurgy. It's object is to obtain the value of a stated quantity (usually in avoirdupois ton) by determining the value of a small representative sample.
- J. Reginald Smith "Assaying For Everyone" 1902
(Printed on Demand)

Modern Assaying: A Concise Treatise, Describing Latest Methods and Appliances (Classic Reprint) (Paperback) - by J. Reginald Smith (Author) Paperback $10.57

So assaying is an attempt to determine the amount and value of a metal in a field, stream bed, mine, or vein.

I think of the Assay Process as functioning like a pinhole camera where:
1. the subject is the mine, 2. the pinhole is the sample, and 3. the image is the emerging estimated amount and value.



A. A rough assay can be done by crushing ore samples and panning the results. With some experience and a careful examination of the amount of gold present, it is possible to make decent visual estimates of the amount of free gold in the ore.

B. Assaying by the blow-pipe furnace is another inexpensive path.

Click here for a list of Assay Tools:

ASSAY PREPARATION

Step 1. Sampling

The first step in assaying is to obtain a sample, and it is all important that the portion selected should be representative of the entire quantity. No special pieces should be picked from the bulk, but the desired quantity is taken indiscriminately from the entire original parcel.

Accurate samples which reflect the true average of the material must be collected. If the sample does not reflect the average nature of the material, no amount of technical accuracy in processing the sample will provide a correct result.
Without a fair sample the assay is useless!

Step 2. Crushing -

Grind or break the entire quantity of the sample to as near as possible a uniform size.

Step 3. Quartering

Now thoroughly mix by stirring and rolling the crushed ore on a large mixing sheet from end to end of the sheet and then from side to side.

Divide into four equal divisions by making a line through the center of the entire sample, and then another line through the center of the sample at right angles to the first line. take the two divisions that are diagonally opposite and discard the balance. Repeat this operation after thoroughly remixing the diagonal portions, and continue doing so until the final remaining two diagonally opposite divisions make such a quantity will furnish pulp (powder) for several assays of the same sample. Care must be used in this operation as the accuracy of the assay depends largely on this.

Step 4. Pulverizing or Pulping



buck-board and muller

It is now necessary to reduce the remaining sample to a fine powder usually called a pulp. This is done by grinding the sample on a flat iron plate with an iron rubber, both of which have smooth surfaces, called a "buck-board and muller." This operation must be done very carefully to avoid losing any of the sample. . . . Use not less than a 60 mesh or preferably an 80 mesh sieve for pulp samples. The idea of pulverizing is not merely to disintegrate the ore so as to expose the minute particles to the action of the flux, but more especially to divide the free gold particles present so uniformly that in mixing the sample no one portion will contain coarser and heavier particles of gold than another.

Step 5. Verify the type of ore to know how much basic and/or reducing flux to add to the pulp:
1. Pure quartz - very glassy or vitreous - add Litharge and Reducing Agent so the slag will suspend the waste.
2. No quartz - Plastic and free from grit - add more silica or glass than usual to the flux.
3. A mixture of the two - add a little silica with the flux.
4. Sulfide ores - if large amounts are present, need to be roasted in a muffle and stirred frequently prior to fluxing.
Lesser amounts can be desulfurized by adding some large iron nails during melting and carefully removing before pouring into the pouring mold.


FLUX
Assay Litharge - Lead Oxide (PbO) - A Reddish, Orange or Yellow Powder milled to a fine and uniform particle size.
Reducing agent such as flour or argol - Potassium tartrate K2C4H4O6 - the potassium salt of tartaric acid.
NOTE: Don't use red lead oxide with silver as it tends to oxidize the silver and drive it into the cupel.

Assay Crucibles are available in sizes of 30, 40, 50, 55 and 65 grams.


A 30 gram crucible = 4 X 3 X 2 1/8" with a volume of 13.2 Cu.in.
A 40 gram crucible = 5 1/16 X 3 1/8 X 2 1/4" with a volume of 18.6 Cu.in.
A 50 gram crucible = 5 1/4 X 4 X 2.4" with a volume of 23 Cu.in.

The crucible commercially known as Battersea "B" or 20 gram size will be found convenient for use when 1 assay Ton of ore is taken; size "F" or 30 gram when 2 Assay Tons are used, together with the necessary amount of flux.
- J. Reginald Smith

Never fill a crucible or scorifier more than three quarters full.

A 20 gram crucible holds 1A.T of pulp = 29.166 grams + 20 grams of litharge + reducing agent?
But what do I know? A question I still need to get answered. - 1dave

Answered by 911Metalurgest - Use a 30 gram crucible for 1 Assay Ton assays, and a 40 gram crucible for 2 ton assays.

Step 6. Weighing the sample



A Fire Assay begins by weighing out:

1 Assay Ton of pulp into each Fire Clay Crucible, then add flux of reducing agent and lead oxide. Stir.
For best noble metal collection from the pulp, Goal is to obtain around a 20 gram "Lead" Button.
Two or more agreeing assays assures accuracy of the reduced sample.
Use a larger crucible and 2 Assay Tons of pulp for lower grade ores to get more gold to weigh.
For High Grade Ores 1/10 A.T. may be desired.

An Assay Ton (A.T.) = 29.166 grams.
Definition of Assay Ton: A weights system created by combining aspects of Troy, Avoirdupois and Gram weights into a simple labor saving calculation unit. It was derived by reckoning in the following manner:

1 lb. av. = 7,000 troy grains.
2,000 lbs. = 1 Ton
2,000 X 7,000 = 14,000,000 Troy grains in 1 ton Av.
480 Troy grains = 1 oz Troy.
14,000,000/480 = 29,166 Troy oz. in 2,000 lbs. Av.
There are 29,166 milligrams in 1 assay ton (A.T.);

Therefore 2,000 lb. is to 1 A.T. as 1 oz. Troy is to 1 milligram.

So now using this system, if 1 A.T. of ore assays 1 milligram of gold or silver, the ton contains 1 ounce Troy.

Step 7. Extracting, weighing, and calculating the values.

There are two methods of assaying:
the "Dry Assay" and the "Wet Assay."

Dry - AKA Fire Assay (assaying proper)- using heat, reducing fluxes. Includes cupellation and scorification.
Wet - AKA Chemical Assay (analysis)- includes volumetric, gravimetric, calorimetric, and electrolic.

Volumetric is the quickest and simplest as less manipulation is required. The sample may often be titrated without lengthy chemical separations.
The weight of ore taken for wet assay is much smaller than is required for Fire Assaying, 1/4 - 2 grams generally being sufficient. It is essential that the sample be finely crushed, especially if it is to be dissolved in acids, as particles of the mineral may be encased in the insoluble gangue. Minerals which are not decomposed by acids are fused with a flux which will render them soluble in water or acids.

The assay of gold and silver may be done by cupellation or by wet chemical volumetric methods. The cupellation method is subject to more errors than the wet assay. If accurate values are needed the chemical method must be applied.

DRY ASSAY



Dry Assay area

Fire Assay Cupels
Cupellation uses cupels traditionally made of bone ash (Ca5(OH)(PO4)3) because they have the ability to absorb metallic oxides. They are designed with a shallow bowl and heavy base for this purpose. Modern cupels have had Portland cement and/or Magnesite (MgCO3) added for strength as they must provide good durability as well as absorption of up to 70% of their weight in grams of lead.

Painting cupels with wet iron oxide to some extent prevents cutting by strong bases.

Magnesite cupels are more robust than their Bone Ash counterparts as they are not affected by temperature changes and are free from cracking and pitting. Magnesite cupels have a rapid rate of lead absorption, and the resulting dore beads are easily removed, minimizing losses.


Standard cupel sizes are #5, 6, 7A, 7AS, 8A, 8S, and 9.

A Fire assay begins with weighing a sample into a crucible and thoroughly blending it with a mixture of dry chemicals such as lead oxide and flour as a reducing agent.
The crucible is then placed into a 1000°C furnace.
The reducing agent reduces the lead oxide to lead. This forms thousands of small droplets of lead, which collect all the precious metals from the sample and sink to the bottom of the crucible.
Meanwhile, the non-precious metal contaminants are carried off into the slag.
The crucible is removed from the furnace, tapped to settle the metal, and poured into a mold.
Never take a scorification or cupellation from the furnace to finish at a future time. Complete the operation at once.
When cool, the slag is discarded and the "lead button" cleaned of any residual slag.
This entire process, therefore, selectively collects all the precious metals from the sample and alloys them with lead.

The next step is "cupellation". A heated cupel has the unique capability of absorbing metallic oxides.
The cupel is preheated to 950°C, then the lead button is placed into it.

Bring two of the cupels forward say within two inches of the front of the muffle. Place a lead button in each, using the cupel tongs, then shove the cupels back into the hotter part of the muffle. Close the muffle door for a few minutes. When the buttons have melted and cupellation has commenced, as shown by the fumes of litharge, open the door and arrange the dampers so that the fumes are drawn slowly off through the rear of the muffle.

Try to keep the temperature constant, increasing it only when the lead has almost disappeared.
The heat is too low when the fumes become heavy and dark, and a scum forms around the edge of the molten lead.
The heat is too high when the fumes of litharge rise rapidly to the top of the muffle and the lead appears to be boiling. The heat is just right when crystals of litharge form in the cupel.

Practice will enable you to fix upon the proper conditions.

The lead melts and the surface oxidizes.
The oxide is absorbed into the cupel, exposing more lead which oxidizes, etc.

As gold and silver do not oxidize until well above 1000°C, they continue to concentrate until the last of the lead is absorbed; leaving only a "dore bead" (containing only gold and silver) in the bottom of the cupel.

After cleaning, the beads' weight is recorded to get the total precious metal content of the sample.
The bead is then ''parted" by dissolving the silver from it with nitric acid which dissolves silver but does not affect gold.
After parting, the weight of gold is recorded.

Subtracting the gold weight from the dore weight provides the silver weight.

The problem with cupellation is that a small amount of gold and more silver is also absorbed into the cupel along with the lead, copper, and other volatile metal oxides.
Fire Assay Errors may be introduced during the following steps.
1. Sample Preparation include contamination from other samples, dilution by impurities, loss of fine particles, drying, and the degree of comminution ( breaking into small fragments) employed.
2. Fusion Process due to improper flux composition, temperature, and the size of the lead button obtained.
These errors cause the incomplete recovery of the precious metals in the lead button.
The metal lost is usually in the slag or crucible, and can be recovered by re-asssaying the slag in the original crucible.





WET ASSAYING


Wet assay area

forum.rocktumblinghobby.com/thread/62873/refining-silver

WET ASSAYING SILVER ORE: Is the same process usually used to Refine Silver.

From 1859 to 1891 the Comstock lode in Nevada produced $325,000,000. This lode is a belt of quartz in a contact vein between diorite and diabase.It is 10,000 feet long and several hundred feet wide.
The Anaconda mine in Butte was one of the largest producers of silver in the country. In 1896 its output was 5,000,000 ounces. The Anaconda was also the heaviest copper producer in the United States, its yield of copper being 125,350,693 pounds.

All silver ores are heavy, and many of them are sectile - may be cut with a knife.
Most silver ores are sulfides as silver easily enters into chemical combinations with sulfur.

In America galena is the principal source of silver. Next are the chlorides and oxides, and finally the silver that is parted from gold when it reaches the mint, as gold always contains some of that metal.
Silver is found in many different locations, and is associated with all sorts of minerals. It is never found in placer deposits, as it easily breaks up under the influence of water, air, etc. It is also found in igneous rocks in association with augite, hornblende and mica.

The commercial ores of silver are:
Argentite Ag2S - - - - - - .- 87.1 per cent silver
Cerargerite AgCl - - - - -. - 75.3 per cent silver
Stephanite 5Ag2SSb2S3 -- 68.5 per cent silver
Proustite 3Ag2SAs2S3 - - - 65.5 per cent silver
Pyrargyrite 3Ag2SSb2S3 - - 59.9 per cent silver

Silver miners have tested ore for silver by heating the ore and dipping it into water.
If silver is present some metal will come to the surface as a greasy scum.

Heated above 600°C silver tends to join with silica to form yellow crystals of silver silicate - Ag2O3Si. For this and other problems the cupellation assay of silver has been largely replaced by volumetric methods. Chief among these is the "Gay Lussac Assay", which was introduced in Paris in 1830 for testing silver bullion.
An exact weight of the bullion is dissolved in nitric acid, and very nearly all the silver is precipitated at once by the addition of a known volume of a standard solution of salt. When the precipitate has settled, the remaining silver is precipitated by the further addition of a small quantity of a more dilute solution of salt, the precipitate forming a white cloud in the supernatant liquid. The quantity of this silver is judged by the appearance of the white cloud.

Wet Assay of Silver Ore:

Begins as all assays - Collecting an honest sample, crushing, quartering, pulping, selecting final samples of 1/4 to 2 grams.

Now place the sample in a tube and dissolve the powdered ore in nitric acid.
The sulfur in the silver is replaced with Chlorine and turns from black to white.
Add a solution of common salt or hydrochloric acid to precipitate chloride of silver.

If chloride of lead and mercurous chloride are absent, then decant or filter the solution.
Dry and weigh the chloride of silver. Three fourths of the weight is nearly pure silver.
Collect and fuse the silver chloride to release the silver.
Weigh the metallic silver collected.

Once you have the weight of the silver extracted from the pulp, the following math will expand the numbers to the weight per ton of silver in the ore:

Weight of the sample in grams / 908000 grams per ton = weight of the sample in tons.

Or Weight of the sample in carats / 155.5 carats per troy ounce = wt. of the sample in ounces.

Next, to determine the ounces per ton, calculate "the Factor":

1/weight of the sample in tons = the Factor

Then the weight of the gold in troy ounces times the Factor = ounces of gold per ton of rock.

Finally, ounces times the spot price = the value.

The web has numerous articles on assaying the other metals. For instance, Platinum is assayed by inductively coupled plasma optical emission spectrometry (ICP OES), which every rockhound should carry in his pocket.

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In "NOTES ON ASSAYING AND ASSAY SCHEMES" BY PIERRE DE PEYSTER RICKETTS Published in 1876 there is a list of tools an assayer would need to haul out into the mining areas to set up shop.

That alone is task enough to stop most people. Try to imagine yourself in that milieu.

Trying to get the knowledge to do the job, building a shack to work out of, gathering the needed equipment out in the middle of nowhere, Then facing those desperate (desperate people do desperate things!) rough miners and the thieves preying on them - Gives one the collywobbles!

Here is the list:

quod.lib.umich.edu/cgi/t/text/text-idx?c=moa&cc=moa&view=text&rgn=main&idno=AEK6695.0001.001

CRUCIBLES. A good crucible should stand sudden changes of temperature, be infusible, impermeable, and not attacked by fused substances. The crucibles in use may be arranged in the following order.
1. Black lead, or graphite for melting.
2. French clay. round and triangular. (Fig. 7.)
3. Hessian sand crucibles (Fig. 8.)
4. Charcoal-lined crucibles.
The most refractory crucibles are cut out of quick lime, or can be moulded from magnesia, and chloride of magnesium, but the latter, however, are soft and not very strong.
The composition of the black lead crucibles is generally one part of refractory clay, to three of graphite; but sand is sometimes used. If the crucibles contain too much silicious matter they are liable to be acted upon by the melted charge, or the bases contained in the coal around them when in the fire. These crucibles run in sizes from 1 to 400. The smallest holding from two to three pounds of metal. The next, four to six, and so on. The demand is for two kinds, "steel" and "brass;" but they can be employed for melting all substances which are not oxydizing in their action.
French crucibles are made of Paris clay and fine sand, and rank among the best, but are more expensive than the Hessian. For melting charges which can be poured they are superior as the crucible can be used again. The sizes run from 1 to 20, with covers to match.
The composition of the ordinary Hessian crucible is about three-quarters clay (German), and one-quarter sand. They are round and triangular, and run in regular sizes, viz: Small fives, large do., up to eights. Halves, holding onehalf gallon, and ones, holding one gallon, with covers to match.

The charcoal crucible is made by lining an ordinary clay or Hessian crucible with a mixture of charcoal and molasses. The charcoal employed should be very fine, and only just enough molasses used to hold it together. The mixture is then packed into the crucible as tightly as possible, dried slowly, and bored out to any extent desirable. Sometimes water and gum are substituted for molasses. Fig. 9 represents three kinds of charcoal lined crucibles. Alumina crucibles for some operations are very satisfactory FIG. 9. when intense heat is required, but lime will answer as well. The choice of a crucible depends upon the nature of the substance to be treated in it, the temperature of the fire, and the time it is to remain exposed to the action of heat. If a charge be basic the crucible should be basic also, and vice versa. To test a crucible for fusibility, heat a piece of the crucible and see if the corners are rounded, or it is fused on the edges. For corosive action fuse litharge in the crucible. For permeability fill two crucibles with water and note the time required for it to run out; the one which holds the best being preferable. The action of sudden changes of temperature may be ascertained by heating suddenly, and cooling first in air and afterwards by plunging in cold water.

ROASTING DISHES, (Fig. 10), and SCORIFIERS, (Fig. 11.) Both dishes and scorifiers are made of refractory clay. FIG. 11. They should FIG. 10. resist the action of litharge and not be too deep. Painting with water and oxide of iron prevents the cutting by strong bases, to some extent. Scorifiers may be bought or made, but as a rule it is better to buy them as they will stand transportation and require some care to make properly. A section of a good scorifier is uniform in character. It is close, and should show no flaws or cracks. (Fig. FIG. Ila. 11a.)

CUPELS. These vessels are generally made of the ashes of burnt bones free from organic matter, ground and washed, horses or sheep bones are said to be the best. Cupels can be bought or made, but the latter is preferable when they have to be carried some distance. The prepared bone-ash can be obtained in bulk, and is mixed with just sufficient warm water to cause it to hold together without being moist. Sometimes in mixing the bone-ash a little wood ashes is added, or a spoonful of "pearl-ash," (carbonate of potash). Before adding it to the bone-ash it is dissolved in water. Too much bone-ash should not be mixed at once, as it dries quickly.

Page 28 28 LUTES. If the bone-ash is too fine or too coarse it works badly; as in the first case the cupel will crack upon drying, and in the second, be too porous, absorb silver with the litharge and occasion loss. The cupel is formed by filling and driving the prepared bone-ash into a mould for the purpose. The right degree of compression should be used, as otherwise the cupel will be either too hard or too porous. A little experience will tell the operator when he has reached the proper point, when completed it presents the FIG. 12. appearance of Fig. 12. Care should be used in drying, plenty of time being allowed, and all moisture and organic matter expelled previous to using, by heating in a furnace. Sometimes a cupel is made of coarse bone-ash, and the surface finished off with fine washed material. Cupels dried in the sun are better than those dried artificially. They are not so liable to crack. In the Royal Mint, London, England, a very fine form of cupel is in use. It is square, with four depressions for holding the same number of buttons, enabling the operator to run two assays in duplicate in the same cupel. Ironbound cupels are sometimes used when the amount to be cupelled is large, especially in treating sweeps. LUTES, CEMENTS AND WASHES. GOOD FIRE LUTES. 1. Fire clay, two parts. Sharp sand, eight parts. Horse dung, one part. Mix well and temper the same as mortar, until the desired consistency is reached.

Page 29 TOOLS. 29 2. Fire clay, one part. Sand, three parts. Mix with a little hair and borax water. 3. Zinc cement. Dissolve three per cent. of borax in water to about 1.49 specific gravity and then add calcined oxide of zinc to suit. OTHER LUTES. Plaster of paris mixed with water, milk, glue, or starch water makes a good lute, and will stand a red heat. Wax or parafine is useful for bottles, stoppers, etc., also tallow or stearic acid. A fine lute for iron vessels is porcelain clay (kaolin) mixed with a solution of borax in water. A good lute for glass vessels, is quicklime slacked in the air and then beaten into a liquid paste with whites of eggs. Where corrosive vapors are liable to escape a lute made of fire clay, and boiled linseed oil should be applied and covered with slips of linen spread with the lute of lime and egg. To LINE CRUCIBLES. Fine sifted charcoal mixed with gum water, borax water, or molasses enough to hold when pressed together in the hand, without being wet or sticky. It should contain no lumps. WASH FOR CRUCIBLES AND SCORIFIERS. 1st. Finely pulverized chalk and water. 2d. Sesquioxide of iron (hematite) and water. TOOLS. The tools required by the assayer are regulated more or less by the work to be done.



Four balances will be found useful in an assay laboratory.

a.- A rough scales for weighing large samples of ores, metals, fluxes in bulk, &c. An ordinary grocer's scale will do very well.
b. - A balance for weighing out ore for assay, and the buttons of the base metals. (Fig. 1). This balance should FIG. 1. take ten ounces in each pan, turn with one-twentieth of a grain; and be provided with movable pans, level, and set-screws for adjusting. It is generally placed on a box, with drawer for weights.
c. - Hanging scales for fluxes. The pans made of horn, and supported by threads to a brass beam. It should carry at least ten ounces, and turn with one-half grain.
d.- The button or bullion scale, (Fig. 2). This balance should be used for nothing but gold and silver beads, or bullion; and must be accurate and extremely sensitive. When loaded with one gramme, it should turn with one one-hundredth of a millegramme, and requires to be handled with the greatest care. It is provided with steel knives, agate bearings, spirit level, and set-screws. To ADJUST THIS BALANCE.-First turn the set-screws, two at a time, until the bubble is in the centre of the level, and the balance is firm. Then note the number of divisions the needle indicates on the scale when vibrated, counting from the second swing. If it shows equally on both sides of the centre line it is correct. Never leave the rest down, or raise it when the needle is not near the centre line, as the knife edges are likely to be thrown off their bearings and the balance injured. To clean, an artist's blending-brush is very convenient, as it is soft and fine.

THE WEIGHTS employed by the assayer area.
a. Avoirdupois for ores, base metals, and fluxes.
b.-Troy for gold, silver, &c.
c.-The French system based upon the gramme as a unit. These weights can be used for weighing ores, fluxes, and results; and will always be found convenient, as they are on the scale of ten.
d.-The assay weights, which is a system made up from a comparison of the three foregoing, will be found extremely simple and useful, saving a vast amount of calculation and labor (see table, page 136). The unit of the system is the assay ton=29.166 grammes. Its derivation will be seen at a glance.

One lb. avoirdupois=7,000, Troy grains. 2,000 lbs. =one ton. 2,000 X 7, 000=14, 000,000 Troy grains, in one ton avoirdupois. 480 Troy grains1= oz. Troy. 14,000,000. 480=29,166+Troy ozs. in 2,000 lbs. avoirdupois. There are 29,166 millegrammes in one assay ton (A.. T.); hence2,000 lbs. is to 1 A. T. as 1 oz. Troy is to 1 millegramme. EXAMPLE. —Weigh an A. T. of ore, and if on assay it yields one millegramme of gold or silver, the result reads one Troy oz. in 2,000 lbs. avoirdupois, without further calculation.

Analytical Balance

Should the assayer desire to make quantitative determinations in the wet way, he will require, besides the above, an analytical balance, which will carry 100 grammes in each pan, and turn with one-twentieth of a millegramme. This balance should be provided with apparatus for taking specific gravities, rider, and weighing-tubes.


The following are the principal:



Crucible tongs (Fig. 13.) They should be made with long FIG. 13. handles for taking crucibles out of the fire, etc.
Scorification tongs. (Fig. 14.) The spring should not be FIG. 14. too strong, and the horse shoe part should just fit the scorifier.
Cupel tongs. (Fig. 15.) These should be made of steel FIG. 15. and about two and one-half feet long with an easy spring.
Three hammers are useful. One large for hammering metal, one medium for breaking crucibles and scorifiers, and one small for marking lead buttons.
A set of small steel dies from 0 to 9 inclusive; and large and small alphabet for marking buttons and bullion will be found useful, but are not necessary.
Three pokers are convenient, small, large, and medium.
One or two small hoes or scrapers for cleaning out the bottom of the cupel muffle. (Fig. 16.) FIG. 16.
A pair of cutting shears and wire snippers for cutting wire for lead assay, etc.
A small vice and anvil, medium size, also a suitable bench for the same.
Wooden mallets, light and heavy, for packing crucibles, making cupels, etc.
Files for sampling and cutting, and several cold chisels.
Charcoal saw for blow-pipe charcoal, and crucible tops.
Several iron mortars and pestles.
If much ore is to be pulverized, a grinding plate and rubber, (Buckboard and Muller)as shown in Fig. 17, will be a great convenience and save labor. The plate is a flat iron casting 18 X 24 inches, and 1 inch thick. The surface used being planed smooth. The rubber or grinder is a piece of cast iron, 4 X 6 inches square, 1 inches in the middle, by 7/8 of an inch thick at the ends; thus giving a slightly convex surface, which should be true on the board at all points. To conduct the operation place the left hand upon the rubber, throwing the weight of the body upon it, and then grasping the handle with the right hand, move the iron rubber back and forth, depressing the handle when pushing forward and raising it in drawing back. The operation is much more rapid than in the ordinary mortar and pestle style, and the manipulator after a little practice has complete control over the ore treated.
Should it not be convenient to have the plate and rubber, a long handled pestle coming up to the chest will be found an improvement, as the mortar can be placed on the floor and the pestle worked while the operator is in a standing position.
A series of sieves, from twenty to one hundred mesh, will be useful for sifting ores and fluxes. The box sieve, (Fig. 18), is a simple arrangement, and consists of a round tin box with a sieve fitting into it as represented in the engraving. The sieve is a tin frame with any desired FIG. 18. mesh gauze soldered to it, and fits tightly in the box. The advantage gained by its use is that in sifting the pulverized ore there is no dust. The fine material being passed through the sieve is kept from flying around. The size most convenient is 8 inches in diameter, the box 2 inches deep, and the rim of the sieve 2 inches, fitting about 3/4 inch into the box.
Open and closed ingot moulds for casting lead and silver bars, ingots, etc.
Hand button rolls for gold and silver only. They should be kept covered and free from dust.
Cupel mould, (Fig. 19.). This consists of two parts, an iron ring and a steel pestle or  driver, just fitting into the ring.
A mould for pouring the assay charge in scorification. (Fig. 20.) This should be of sheet iron or copper, and not too thin. It saves much time, and by employing it, the scorifiers can be used again.
Shovels for coke and coal, also a small hatchet for splitting kindling wood. The coke shovel should be ribbed or perforated so that the fine coke or dust may fall through.
Mixing scoops of Russia sheet iron 3 by 5 inches, with straight sides and FIG. 20. back about I inch high. They are convenient for mixing lead or silver crucible charges in, and owing to the high finish of the iron, the assay on being poured out does not cling to the scoop; a few sharp taps detaching everything.
A tin sampler, shown in Fig. 21, will be found very useful. It consists of a series FIG. 21. of troughs arranged in a row and fastened together at equal distances by a tin strip soldered on their ends.

A shovel full of ore emptied by a series of shakes upon them, is just half caught by the troughs; one-half going through the openings between. By repeating this operation, the size of the sample can be reduced to any extent desired.



A laboratory desk, as shown in Figs. 22 and 23, will be III f _ I FIG. 22. Section. FIG. 23. Elevation. Scale Y2 inch to the foot. Scale X inch to the foot. found a very suitable arrangement, and very compact, consisting of four parts, shelves for bottles, closet for ore scales, drawer for cupels and apparatus, and double closet for crucibles, scorifiers, etc. The illustrations being made to a scale, the desk can be constructed from them without trouble. This style of desk has been in use in the School of Mines, New York, for some years, and has been found most convenient. The lower closet should be provided with a shelf and the drawer with partitions.

If gas can be had, each desk in a laboratory should have a burner above for lighting purposes, and two or three large jets to which rubber tubes can be fastened so that Bunsen burners can be employed on the desk. These jets are best placed next the scale closet.

APPARATUS.
The amount and kind of apparatus required by the assayer varies; but the following list will be found about all that will be needed for ordinary work:
About three dozen quart bottles for reagents, glass stoppered.
One dozen parting bottles, glass stoppered for bullion assay. Eight oz. is a good size. The stoppers should be square-topped and fit exactly, so that the bottles will not leak when shaken.
An assortment of corked bottles of different sizes for samples.
Two or three ring stands and the same number of Bunsen burners or alcohol lamps. The former are preferable, if gas can be had, and should be provided with two or three feet of rubber tubing for each burner.
Two wash bottles, one small and one large, say one-half pint and pint.
One half-dozen horn spatulas or spoons for mixing ore.
Some iron pans for roasting. The ordinary long handled frying pan is suitable, and should be about the size of the furnace top. Before roasting it should be lined with chalk or oxide of iron.
One dozen parting flasks, (Fig. 24,) for gold bullion assay; also annealing cups for the same purpose. These are of clay and made thin. (Fig. 25.)
Brushes for ores and fluxes made of FIG. 24. FIG. 25.camel's hair; or a large feather trimmed, makes an excellent substitute.
A few dozen sheets of glazed paper, or stout manila paper when glazed paper cannot be had, for mixing ore upon. Black is preferable, and when held up to the light, there should be no small holes.
Hessian and French crucibles and covers of various sizes and shapes.
Scorifiers, large and small.
Scorification and cupel muffles to suit furnaces.
Cupels from 1 to 11 inches in diameter. These should always weigh more than the button to be cupelled.
Glass beakers and rods.
Funnels for filtering.

Gum labels, note book, towels, large and small porcelain mortars, balances, scales and weights, as have been described.

For volumetric work, silver bullion, etc., graduated flasks, pipettes and burettes, will also be necessary. See bullion assay, page 102. Should the assayer wish to be prepared for all kinds of work, it would be well for him to provide himself with the complete list on pages 167 and 168, appendix, or at least iron, clay and glass retorts, agate mortar (large), one or two platinum crucibles and dishes, and a couple of Bunsen battery cells.

These may be divided into six classes.
a. Reducing. To this class belong those bodies which have the power of removing oxygen from its combinations.
b. Oxidizing. All bodies which give up oxygen with facility.
c. Desulphurizing. This class includes all substances which possess a strong affinity for sulphur, and will decompose its compounds under the action of heat or in solution.
d. Sulphurizing. Sulphur and such of its compounds as give up their sulphur easily upon elevation of temperature or in solution.
e. Fluxes. Under this head, we include a large class of bodies, but generally they are substances which render others to which they are added more fusible. Either by acting as a solvent or as a decomposing agent. Fluxes are either acid, basic, or neutral in their action.
f. Solvents include solutions which are used in the wet way only. Such as distilled water, nitric, sulphuric and hydrochloric acids, etc.
g. Precipitants in the wet way. As in the salt solution used in the bullion assay.

The following are the principle reagents and chemicals employed by the assayer in his work.
There are, however, many others which might be used, but they can all be classed under the heads just given.

BICARBONATE OF SODA (sodic bicarbonate, Na HCO,) or the corresponding potash salt. These act as desulphurising agents, and in some cases as oxidising agents. The latter action being due to the carbonic acid contained. Sometimes they act as basic fluxes. They should be free from moisture, and lumps. On account of their easy fusibility they can retain in suspension, without losing their fluidity.

A large proportion of finely powdered infusible substances.
LITHARGE (PbO), is a basic flux, oxydizing and desulphurizing agent, and supplies the lead in the gold and silver crucible assay. It should be dry, and free from red oxide of lead, as the latter has the power of oxydizing silver, and thus causing loss of that metal during the assay. To free litharge from the red oxide, fuse the same in a crucible, and pour the mass into a cold ingot-mould, keeping it from the air while cooling. All litharge before using should be well sampled, and assayed for silver. To do this, charge in a crucible Litharge............ 4 A.T. Soda............... 2 " Charcoal........... 1 gm. and cover with a layer of dried salt, one-quarter of an inch thick. Fuse in a hot fire until completely liquid, then withdraw, and proceed as in the assay of a silver ore (p. 66).
White lead (carbonate of lead-plumbic carbonate PbCO,), is sometimes employed instead of litharge; also, acetate of lead for delicate experiments.
BORAX, CRYSTALLIZED (2NaBO,.B,0+10H,O).-This acts as an acid flux; but, on account of the water contained, it is generally employed in a vitrified condition, or borax glass (2NaBO2.B2,), which has a more intensified effect. It has neither an oxydizing or desulphurizing action. To prepare-Fuse the commercial borax in a chalk lined crucible, pouring the fused mass out on a clean surface to cool. Pulverize, and keep in a glass-stoppered bottle as borax, when heated, loses its water of crystallization, and undergoes an immense increase in volume, only a little should be added at a time in fusing.
Boracic acid (HBO,) is also sometimes used.
SILICA (SiO,), acts as a good acid flux, and can often be used with advantage.
A good substitute is glass (NaSi, O,+CaSi,07+SiO,), as it is easily fusible, and forms a good slag. It should be powdered and free from moisture. Lime glass is the best.
BLACK FLUX, SUBSTITUTE.-A mixture of three parts flour and ten parts of bi-carbonate of soda acts as a flux and reducing agent, and is especially useful in the lead assay. Black Flux, proper-1 of nitre and 3 of argol-deflagrated.
CYANIDE OF POTASSIUM (potassic cyanide KCy-KCN), as a flux for reducing and desulphurizing is invaluable. It should be prepared with care and kept in a tight bottle, as it absorbs moisture. Take the ordinary commercial article and pulverize in an iron mortar as fine as possible. Never sift, as the dust is poisonous. To protect yourself, cover the mortar with a towel, or a board having a hole in the centre for the pestle.
FERRO-CYANIDE OF POTASSIUM (yellow prussiate of potash)(potassic ferro-cyanide K,Cfy=4KCY,FeCy2), will often be found useful as a flux for reducing and desulphurizing. The crystallized material should be powdered in a porcelain mortar, and dried over a slow fire until it is almost white. If the heat is too high it will carbonize and turn brown.
ARGOL (KHCHO46), crude bitartrate of potash, acts as a basic flux and reducing agent. It should be pulverized and dry, and its reducing power determined. For this purpose we charge Argol............... 2 gms Litharge............ A.T. Soda................ " in a crucible, fuse in a hot fire, cool, extract the button and weigh in grammes. Dividing by two gives the amount of lead one gramme of argol will reduce from litharge.
CHARCOAL, acts as a reducing agent and desulphurizer. It should be finely powdered and its reducing power determined, as in the case of argol. Using one gramme instead of two as in that assay. Ordinary wood charcoal will reduce twenty-eight grammes of lead from litharge.
STARCH n(C6H1,O,)(C,,H,,012 ), sugar, and gum, may also be used for reducing agents, but are not so convenient. Dried starch reduces thirteen parts of lead. Common starch about eleven and one-half parts. Sugar fourteen and one-half, and gum arabic eleven parts.

For some purposes pure hydrogen gas will be found essential as in the assay of oxide of tin. It is the strongest and best reducing agent, but requires care in its preparation. It is made by dissolving zinc in dilute sulphuric acid, and passing the gas evolved through oil of vitrol, to dry it before using. One part of hydrogen will reduce about one hundred and four parts of lead from litharge.

METALLIC IRON (Fe), is a desulphurizing agent, and is indispensable, especially in the assay of lead ores. The best form is iron wire about - inch in diameter. Nails and filings may also be used.
PURE LEAD (Pb), in sheet or granulated form, is used principally in the assay of silver ores. It acts as a basic flux, and a solvent or wash for the precious metals. The sheet form is useful in cupelling gold and silver beads, and in the bullion assay. The granulated is essential in the scorification assay. It can be obtained pure by decomposing the best white lead by charcoal, and granulating or fusing in bars, as the case may require. In sections where granulated lead free from silver, or white lead, cannot be obtained, the assayer can make his own granulated lead from bar lead, poor in silver, by the following method:-Melt about fifty pounds of bar lead in an iron pot or crucible, and keep it just at the melting point. Then pour a ladleful of the melted lead into a wooden bread-tray which has been well chalked on the inside. Keep this agitated by gently rocking the tray to prevent solidification, and when the mass begins to get pasty, throw it into the air and catch it again repeatedly until cold, when the metal will be found to be nearly all granulated. Sift through a twenty-mesh sieve, and what does not go through re-melt. The whole fifty pounds can be granulated in this way in two hours. After granulation sample well and test about thirty to fifty grammes for silver, by the scorification assay. In using the lead, the silver contained in it must be deducted from the results in assaying an ore.
NITRE (potassic nitrate KNOS), acts as a basic flux and oxydizing agent. It should be finely powdered, dry, and assayed for its oxydizing power. Charge: Nitre.............. 3 gms. Charcol............1 " Litharge........... A.T. Soda............... 1 " Place in a Hessian crucible and cover with salt. Fuse in a hot fire, remove, cool and weigh. The difference between the weight of the button obtained and that given in the assay of charcoal, divided by three, gives the oxydizing power of nitre per gramme.
POWDERED LIME (CaO), (dry), and fluor spar (Ca F2), will often be found useful as basic fluxes, especially in the assay of iron ores. Magnesia (Mgo), and alumina (A120,) or kaolin (Al, 0.2SiO,)-are also used, and cryolite (3NaF. Al1F) for tin ores.

AS SULPHURIZING AGENTS: powdered sulphur (S), pure galena (PbS), or sulphide of antimony (SbS,), are employed. CARBONATE OF AMMONIA (ammonic carbonate (NH4),CO,), as a desulphurizing agent, is used in the decomposition of some sulphates, as sulphate of copper, in roasting. It should be powdered and kept in a close vessel. COMMON SALT (sodic chloride NaCl), as a cover and wash, and as a reagent in the bullion assay, should be always kept on hand. The purer it is the better, and it must also be fine and dry.

AS SOLVENTS AND PRECIPITANTS - distilled water (H,0), sulphuric acid (H,SO0), nitric acid (HNO,), hydrochloric acid (HC1), chloride of sodium, nitrate of silver (argentic nitrate AgNO,), and sulphuretted hydrogen (HS), are most frequently employed. The acids may be purchased pure. Nitric acid should be free from chlorine, which can be separated by the addition of nitrate of silver, drop by drop, until a precipitate ceases to form. The clear acid, after settling, being drawn off with a syphon. Nitrate of silver may be made by dissolving pure silver in nitric acid free from chlorine; evaporate to dryness and dissolve one part of the salt in twenty parts of distilled water.

Sulphuretted hydrogen is best prepared from powdered sulphide of iron (ferrous sulphide FeS) and dilute sulphuric acid. The gas being passed through a second bottle filled with water to wash it. Fig. 26 shows the apparatus in position for use The glass tubes are connected with small pieces of rubber tubing. The gas may be passed into a solution to be precipitated, or a water solution may be saturated and used at pleasure.

The sulphide of iron can be made by heating scrap iron or borings to a red FIG. 26. heat in a crucible and throwing in sulphur. The sulphide produced may be then fused or broken up, still-fusion is unnecessary. OTHER CHEMICALS and reagents will often be found necessary if assays in the wet way are to be made, but the reader must be referred to page 168. The most important are arsenic (As), arsenide of iron (ferrous arsenide Fe2As), hyposulphite (NaiH,S,0,) and sulphide of sodium (Na2S).

[Admin]

Assaying With the Blow Pipe
Assay by Blowpipe - is simpler, less expensive, and far easier to set up than standard assaying.
Instead of huge furnaces, it can be done with a Bunsen burner, Alcohol lamp or even just a Candle.

The blowpipe assay for silver, first proposed by Harkort, and described by him in a work that appeared in Freiburg, in the year 1827, is one of the most important assays that can be made with this instrument.
It is possible not only to detect in a short time the silver in any ore, mineral, or product, but also to determine its amount qualitatively with all needful accuracy.
- Karl Friedrich Plattner

All of the needed equipment could be purchased in one kit -

Fine Blowpipe Set for both qualitative and quantitative analysis. Made by C. Osterland, Freiberg, Germany. All contained in polished mahogany box,13 1/2 X 12 1/2 X 4 1/2 in., with brass grip handle at one end. Enclosed in stout leather case with straps ; weighs complete, 22 1bs. Contains the following implements, all of finest construction, brass and nickel finish, packed in velvet lined recesses, in trays and in tin boxes:

List of items:


Simple Blowpipe Assay Instructions -Kit 279. - Refer to Fig 1.

First, Fusion. Weight two grammes of pulp or well mixed ore, and mix with it eight grammes of pure granulated lead in the scorifier, then cover the mixture with eight grammes more of the lead, then by means of the pipette add drop by drop concentrated phosphoric acid until the mixture is moist. The object of this is to cement the pulp into a compact mass to prevent its being blown away by the blast.

Place the scorifier (D) with its charge into the furnace as shown in Fig 1.and let it rest quite level upon its asbestos bed with loose asbestos around the sides of the scorifier, even with the top, as at E. Now blow a smokey flame upon the surface of the assay to expel moisture, then add to the assay ten or twenty percent of borax glass as the ore may require.

The cover (A) is now placed on the scorifier as shown, but care must be taken that the openings (A and B) are just large enough to let the flame in at A and the gas escape at the opening B.

The most difficulty is experienced by beginners in obtaining a flame which is of sufficient volume and intensity to bring the ore to fusion. The paraffin in the lamp (G) must first be melted, and the copper tube, which carries the wick, heated by means of an alcohol flame and mouth blowpipe before the lamp is lit. The wick should be cut to an angle of about thirty degrees. The flame when burning freely should be about five inches high.

Particular care must be taken with the platinum blowpipe tip. It is bored to the width of 1/10 millimeters, and the hole is true and in line with the axis of the cone, and it should be preserved from injury. If this is not the case the flame will scatter and buzz, in which case it is impossible to obtain fusion. The blowpipe flame must be perfectly smooth and silent, when the furnace, lamp and blowpipe are in the position shown in Fig 1. The bellows are operated so as to produce a flame which is slightly yellow at A, but nearly blue at C. This flame is kept up until fusion is completed, then the flame is moved a little in the direction of the furnace, which will shorten the flame so that the point will barely strike the surface of the molten lead. Care must, however be taken that the temperature of the furnace does not drop to the extent as to chill the slag. The blast is kept up until the lead is oxidized to such an extent as to be nearly covered with slag. The scorifier is then removed from the furnace and allowed to cool.

SECOND, CUPELLING - The lead button is prepared in the ordinary way for cupellation.
The cupel is made by taking a new scorifier and filling it with dry bone ash and pressing down the surface as hard as you can, and smooth, with a depression in the center about 5/8 of an inch in diameter and 1/16 of an inch deep. A wood former is provided for this operation.

The cupel, prepared in this way , is placed within the furnace (without a cover), as Fig. 2., and heated and heated with the blowpipe flame until all the moisture is expelled. Then the lead button is placed I the cavity for cupellation.

The flame is held directly on the lead until the litharge begins to form. After this it is necessary to keep the point of the blue flame at one side of the molten lead. The object of this is to keep the bone ash at a sufficiently high temperature to absorb the litharge as fast as it is formed. Close attention must be paid to this part of the operation.

The flame should be directed to any point where litharge is inclined to accumulate, otherwise the operation is as the ordinary cupellation in the muffle furnace.

The most difficulty is experienced by beginners in obtaining a flame which is of sufficient volume and intensity to bring the ore to fusion.

For this reason Blowpipe Assaying dropped off for a while but new inventions came to the rescue.


Blowing into the blowpipe forces the water level down. This maintains the air pressure while taking the next breath.


stand to keep the blowpipe steady, and hand pump to save the breath.



With the Invention of the Hoskins' gasoline fueled blowpipe, heat was no longer a problem.

In general it may be said that the average careful student, with some experience, should obtain results with silver ores easily within ± 10% of the values obtained by the regular fire assay. While it is not claimed that these methods will ever replace the regular fire assay, still for fairly close approximations in field or laboratory these methods seem eminently satisfactory.

NOTES
1 Plattner's Blowpipe Analysis; translated by Henry B. Cornwall Eighth edition, revised. D. Van Nostrand, New York. 1902.
2 Quantitative Assaying with the Blowpipe, E. L. Fletcher. John Wiley & Sons. New York. 1906. This will be found an extremely helpful text for those wishing to become proficient in this work.
3 Note on Assaying, Richard W. Lodge. Third edition, 1911, p. 190. John Wiley & Sons. New York.
4 Notes on Assaying, Richard W. Lodge. Third edition, 1911, p. 213. John Wiley & Sons. New York.
5 To determine the amount of silver in argentiferous galena the charge to be recommended consists of: ore 600 mg., Na2CO3 300 mg., KNO3 400 mg. and salt cover.

With the advent of the Fletcher Blowpipe Furnace#2 a new impetus was given to blowpipe assaying. The size of the charge can easily be doubled and the effects of time of fusion or the influence of variation in flux can be more readily ascertained. Also, inasmuch as the general scheme employed is that of the ordinary fire assay, no manipulation is necessary during the fusion period, thereby reducing the personal technique to a minimum and making it possible for the average careful student to obtain very satisfactory results.
- WALTER F. HUNT, University of Michigan

Instructions in Greater Depth:
BLOWPIPE ANALYSIS, APPARATUS AND REAGENTS.
ia802604.us.archive.org/13/items/notesonassaying02rickgoog/notesonassaying02rickgoog.pdf pp175-187.

The assayer will find that a knowledge of the proper use of the blowpipe will prove a great saving of time and labor, by enabling him to more fully understand the character of many substances presented for assay, which he could not otherwise determine save by qualitative analysis. The first and most important thing in blowpipe analysis is to learn to blow and breathe at the same time, without removing the mouth from the instrument or interrupting the blast; this can be done by filling the mouth with air and breathing through the nose, expelling some of the air into the mouth at each breath.

The blowpipe flame consists of two distinct portions.
1st. The outside or oxidizing flame;
2d. The inner blue cone, the point of which is the hottest part of the flame. Its action is reducing. This flame is obtained by putting the point of the blowpipe about one-quarter of the way into the lamp flame.



The true reducing flame is entirely yellow, the blowpipe point being held just outside of the lamp flame. The substance to be tested should be-finely powdered and treated:



1st. On charcoal. This is best done by making a small hole in the right hand corner of the coal, nearest the lamp, placing a little of the substance in the same and testing first with the oxidizing and then with the reducing flame, noting the action of each and the color of the coating formed, etc. The holes in the charcoal should be bored on the edge of the grain to avoid splintering. Blow across the coal.
2d. If the substance treated gives off volatile fumes on charcoal, test a little of it in a closed and open tube successively, first alone, and then in the closed tube with a little carbonate of soda. Note the coating formed and the color and order of the fumes.
3d. Test the substance with the borax, salt of phosphorus, and soda beads successively; this may be done on platinum wire or, if the substance be metallic, on charcoal. To make the proper sized bead, bend the end of the wire into a loop on the point of a sharp pencil, dip it into the reagent and melt before the blowpipe until a clear, good bead is formed, then add the substance and heat, first in the oxidizing and then in the reducing flame.
4th. Apply special tests, as the color of the flame, the action of nitrate of cobalt on the coat formed on charcoal; adding the cobalt solution and then heating.

If the substance is not metallic the color of the flame can best be noted by testing in the platinum pointed forceps; moistening the material with hydrochloric acid, and bringing it into the tip of the blue cone of the blowpipe flame.

To get the methods of performing the above operations the following substances will serve as type examples:
To test blowing and flames, oxide of manganese and molybdic acid.
To test on charcoal, lead and antimony.
To test in the matrass or closed tube, cinnabar and arsenic.
To test in the open tube, stibnite and sulphur.
To test with the beads. Borax bead, oxide of copper. Salt of phosphorus, the same and sesquioxide of iron. Soda bead, manganese and chromium.

CHARACTERISTIC TESTS.

Potassa, colors the flame violet; best seen through a blue glass.
Soda, reddish-yellow flame.
Lithia, carmine-red flame.
Ammonia, colors red litmus-paper blue, pungent odor.
Baryta, burnt with alcohol gives a yellowish-green flame.
Strontia, crimson flame.
Lime, colors the flame feebly red, becomes caustic and glows when heated.
Magnesia, gives with nitrate of cobalt a pale flesh-color, after long blowing.
Alumina, gives a fine blue color with nitrate of cobalt.
Silica, in Sp. Ph. bead gives a semi-transparent skeleton floating in the bead.
Oxide of antimony, on charcoal, is reduced, and gives white fumes and coat and greenish-blue flame.
Arsenious acid, with soda on charcoal, gives white fumes and garlic odor.
Oxide of bismuth, on charcoal, is reduced to metal, and gives an orange-yellow color.
Oxide of cadmium, coats the coal with a reddish-brown powder and variegated tarnish.
Oxide of chromium, with soda in the 0. F. gives a yellow glass; in R. F., green on cooling.
Oxide of cobalt, on charcoal becomes magnetic. With borax and S. Ph. beads, smalt-blue glass. Oxide of copper, metallic button on charcoal. With borax bead, green glass, blue when cold; red in R. F.
Oxide of gold, with borax on coal easily reducible to metal. Oxide of iron, on coal becomes magnetic. Borax bead, red to yellow on cooling; in R. F., bottle-green.
Oxide of lead, reducible to metal on charcoal with sulphur-yellow coat and blue flame.
Oxide of manganese, with soda, on cooling bluish-green, With borax, amethyst bead, colorless in reducing flame.
Oxide of mercury, volatile on charcoal, metallic mirror with soda in closed tube.
Molybdic acid, with S. Ph., yellowish-green, and colorless when cold. The bead on coal becomes green on cooling.
Oxide of nickel, on charcoal, yields a magnetic powder. Borax bead, reddish-brown.
Oxide of silver, on charcoal, reducible to metal. With borax, opalescent or milk-white glass.
Oxide of tin, reducible on charcoal to metal with yellow coat, white when cold. With cobalt solution in O. F., gives a bluish-green color.
Titanic acid, with salt of phosphorus bead in R. F., a fine violet color.
Oxide of zinc, yellow coat on coal, white when cold. With cobalt solution, green in O. F. Chlorine, with oxide of copper in borax bead a fine azure blue flame.
Iodine, with soda, or better, bi-sulphate of potash; in matrass, violet fumes.
Bromine, with bi-sulphate of potash in matrass, reddish yellow vapors.
Fluorine, etches glass when mixed with a little sulphuric acid.
Carbonic acid, acid reaction, turns lime-water white.
Sulphur, burns on charcoal with a blue flame with odor of sulphurous acid; better in open tube.

SCHEME FOR BLOWPIPE ANALYSIS.

The substance may contain As, Sb, S, Se, Fe, Mn, Cu, Co, Ni, Pb, Bi, Ag, Au, Hg, Zn, Cd, Sn, C1, Br, I, CO,, SiO,, HNO,, H,O, &c.

The abbreviations O.F., R. F., Ch., and S. Ph., stand respectively for oxidizing flame, reducing flame, charcoal, and salt of phosphorus.

1. Treat on Ch. in the 0. F, to find volatile substances, such as As, Sb, S, Se, Pb, Bi, Ag, Zn, Cd., &c.
a. If there are volatile substances present, form a coating and test it with S.Ph. And tin on Ch. For Sb. Or to distinguish between Pb and Bi using the R.F.

b. If there are no volatile stances present, form a coat- substances present, divide a part of the substance into three portions and proceed as in A

Sb. gives gray bead, clear on long blowing; Bi. clear and colorless when hot, blackish-gray and opaque on cooling; Pb. cloudy and dark, but never quite opaque. In testing for Bi. the antimony must be driven off first.

If Sb. is present it is not necessary to look for Bi and vice versa. These two substances are very rarely found together. The same is true of Pb and Bi.

2. If As, Sb, S, Se are present, roast a large quantity thoroughly on Ch. in the 0. F. Divide the substance into three portions, and proceed as in A.

A. TREATMENT OF THE FIRST PORTION. -Dissolve a very small quantity in borax on platinum wire in the 0. F. and observe the color produced. Various colors will be formed by the combination of the oxides. Saturate the bead and shake it off into a porcelain dish.

a. Treat the bead on Ch. with a small piece of lead, silver or gold, in a strong R. F. Lead can be used instead.

b. Fe, Mn, Co, &c., remain in the bead. If the bead spreads out on the Ch., it must be collected to a globule by continued blowing.
Make a borax bead on platinum wire and dissolve in it some of the fragments of the bead, reserving the rest for accidents.

c. Ni, Cu, Ag, Au, Sn, Pb, Bi are reduced, and collected by the silver or gold button.
Remove the button from the bead while hot, or by breaking the latter when cold on the anvil between paper, carefully preserving all the fragments.

d. If Co is present, the bead will be blue.
If a large amount of Fe is present, add a little borax to prove the presence or absence of Co by diluting the bead, the cobalt color being more intense.
If Mn is present, the bead when treated on platinum wire in the O.F. will become dark violet or black.

e. If only Fe and Mn and no Co be present, the bead will be almost colorless.

f. look here for CR, Ti, Mo, and W. Mo will give a cloudy-brown or black with the borax bead in the R.F.; owing to the molybdic acid being reduced. Cr gives yellowish-green with borax bead; yellow with soda bead; emerald-green with S.Ph. Tin in S.Ph. Bead gives fine violet color; best seen with tin on charcoal. W, a fine blue color, under the same conditions.

g. Treat the residue on Ch. in 0. F. with S.Ph. bead, removing the button while the bead is hot.

h. If Ni and Cu are present, the bead will be green when cold. If Ni only-yellow. If Cu only-blue. Prove Cu by treating the S.Ph. bead with tin on Ch. in the R. F., the bead becomes red on cooling. Ni and Cu may be separated by fusing them with a gold button of equal weight and oxidizing with borax or S.Ph. The Ni is dissolved first in the borax glass.

i. For Ag and Au make the special test No. 8.

B. TREATMENT OF THE SECOND PORTION.-Drive off the volatile substances in the 0. F. on Ch. Treat with the R. F., or mix with soda, and then treat with the R. F., for Zn, Cd, Sn. If a white coating is formed, test with cobalt solution and observe the color. Tin gives greenish-blue, zinc, green. If Zn is found, it is not necessary to look for Sn, and vice versa, as they very rarely occur together. Cd. gives a brown coat and variegated tarnish.

C. TREATMENT 'OF THE THIRD PORTION.-Dissolve some the substance in S.Ph. on platinum wire in 0. F., observing whether SiO is present or not, and test for Mn with nitrate of potassa, and soda.

3. Test for As with soda on Ch. in the R. F., or with dry soda in a closed tube. On charcoal it gives garlic odor; in the tube, a metallic mirror.

4. Dissolve in S.Ph. on platinum wire in the 0. F. (if the substance is not metallic and does not contain any S.) and test for Sb on Ch. with tin in the R. F. See 1, a.

5. Test for Se on charcoal; it gives a horse-radish odor.

6. In the absence of Se, fuse with soda in the R. F. and and test for S on silver foil. By moistening the fused mass and letting it stand on the foil the latter turns black if S be present. In the presence of Se test in open tube.

7. Test for Hg with dry soda in a closed tube; a metallic mirror is formed.

8. Mix some of the substance with assay lead and borax glass and fuse on Ch. in the R. F. Cupel the lead button for Ag. Test with nitric acid for Au, dissolving the silver.

9. Test for Cl and I with a bead of S.Ph. saturated with oxide of copper. Cl gives blue flame; I, intense green.

10. Test for Br with bi-sulphate of potassa in a matrass, gives brownish-yellow fumes.

11. Test for H20 in a closed tube; drops collect on the interior.

12. Test on platinum wire, or in platinum pointed forceps, for coloration of the flame.

13. Test for CO, with hydrochloric acid, letting the gas pass over lime water.

14. Test for HNO, with bi-sulphate of potassa in a matrass; yellow colored fumes, and acid reaction.

15. Test for Te in an open tube; forms a grayish-white sublimate which fuses to clear, transparent drops when strongly heated. Te burns with a bluish-green flame.

The above scheme is essentially the same as the one used by the students of the School of Mines, New York, prepared by Prof. Thos. Egleston. A few changes have been made so as to render reference to works on blowpipe analyses unnecessary.

Again, the above abbreviations O.F., R. F., Ch., and S. Ph., stand respectively for oxidizing flame, reducing flame, charcoal, and salt of phosphorus.

BLOWPIPE APPARATUS.

Blowpipe, with platinum jet, in three pieces, with cylinder to catch the moisture.
Lamp, for blowpipe, with swivel and stand, four pieces.
Lamp, alcohol, with brass cover ground to fit, for lighting large lamp.
Forceps, steel, nickel plated (Raynor's), for testing color of flames.
Forceps, brass, to handle small buttons, beads, etc.
Forceps, steel, for lamp, to raise wick with.
Plyers, cutting, for clipping minerals, sampling, etc.
Plyers, flat nose (nippers) for quantitative work, handling lead buttons.
Holder, cupel with two cups and one mould, for cupelling lead buttons.
Holder, charcoal, with platinum ring and shield, for quantitative work.
Holder for evaporating dish, with triangle, for parting, making solutions, etc.
Holder for chimney, to concentrate the flame of alcohol lamp.
Holder for platinum wire, with six wires, for making bead tests.
Holder for matrass (a rounded, long-necked glass container, formerly used for distilling and dissolving substances. ), to hold tubes, etc.
Hammer, for breaking slag, pounding buttons, etc.
Anvil, for breaking slag, pounding buttons.
Borer, charcoal, club shape, to make holes in charcoal and coals.
Borer, charcoal, four-cornered, to enlarge coal crucibles for quantitative work.
Borer, charcoal, with spatula, for quantitative work, useful in boring out coals.
Capsule, mixing, brass, gilded, to mix charges for quantitative work in.
Spatula, mixing, steel, for mixing charges.
Spoons, ivory, two, for measuring out reagents, etc.
Brush, assay button, for cleaning buttons before weighing.
Charcoal saw, to shape charcoal.
Tray, for coal, for quantitative work, mostly.
Tray, for dirt.
Scissors, for lamp, to trim, etc.
Knife, small, with long thin blade.
Magnifier, with two lenses, to examine minerals.
Magnet, bar with chisel edge, to test for iron, nickel and cobalt.
Form for paper cylinders, for quantitative work.
Test lead measure, " "
Small camel's hair brushes, to clean up with.
Moulds for making crucibles, coals, and capsules.
Steel mortar for crushing minerals.
Agate mortar for pulverizing.
A small glass wash bottle.
Small platinum spoon for fusions.
Scales for quantitative work; a bullion balance will do as well; also a measuring scale for buttons.
Glass matrasses, closed and open tubes, porcelain dishes and capsules, and clay cylinders for coal crucibles.

For quantitative work the assayer will also require:
Coal crucibles and capsules.
Clay " "
Square coals and covers.

BLOWPIPE REAGENTS.
Carbonate of soda, pure and dry.
Neutral oxalate of potassa. pulverized.
Cyanide of potassium, pulverized.
Iodide of potassium,
Borax and borax glass, pulverized.
Salt of phosphorus (phosphate of soda and ammonia).
Nitre (crystals).
Bi-sulphate of potassa, pulverized.
Vitrified boracic acid, in small fragments.
Nitrate of cobalt in solution.
Test lead, finely granulated.
Tin, in foil best.
Iron. Wire or pieces of 1/2" to 1" long,
Gold, in foil.
Arsenic, metallic,
Test papers, blue and red litmus.
Salt, pulverized and dry.
Fluorspar, fine and dry.
Silica, ignited and white.
Oxide of copper.
Chloride of silver, in paste.
Starch meal.
Graphite, fine and pure.
Concentrated sulfuric, nitric, and muriatic acids. Acetic acid.
Carbonate of ammonia in powder.
Charcoal cut in blocks 3" X 3/4" X 1/2".
Sifted and washed bone-ash.

GENERAL REMARKS.
To clean a dirty platinum point hold it in the flame of the alcohol lamp with the platinum pointed forceps.
To clean platinum wires, heat and plunge into muriatic acid. To break small pieces of mineral, wrap in paper or cloth before hammering.
To trim tie wick of blowpipe lamp, cut even with the lamp and raise with one point of the steel forceps; Never pull up with the forceps.
To light the usual blowpipe lamp, where a heavy oil is used, direct the flames of an alcohol lamp against the wick until it ignites.


For the absolute best blowpipe instructions download this 600 page book by Plattner:

ia801406.us.archive.org/27/items/plattnersmanual02platgoog/plattnersmanual02platgoog.pdf

[Admin]

In addition to the OCR I was able to download the original book this morning so I now have access to the drawings. Here are the Assayers Furnaces.

Page 21 FURNACES AND FUELS. 21 FURNACES AND FUELS. 1st. FURNACE FOR CALCINING OR ROASTING.- Fig. 3 represents two sections. The fireplace is made shallow; and, as a high temperature is not required, it may be'' 1 made of red brick, or only lined with fire-brick, and the body of the furnace bound with strap-iron. It should also have a castiron top-plate. The grate-bars may be in one piece or separate, and...'draw out. The ash-pit should'Blll~ J~ be provided with a door, which may be closed or opened in order to regulate the draft. A hood of sheet-iron will FIG. 3. Scale P-inch to the foot. also be found necessary in many cases, as the fumes given off in roasting are often injurious. It is an excellent plan to have the hood of galvanized iron to prevent, rusting. The chimney may be of brick, iron or clay. 2d. FURNACE FOR FUSION OR MELTING (Fig. 4).-This furnace should be deeper than the. preceding one, and like it, may be built of red brick, but' it is better to line it with fire brick. For heavy work the furnace should be low, to facilitate

Page 22 "22 FURNACES AND FUELS. the lifting in and out of crucibles. Sometimes a crane is added for this purpose. The chimney D -E~ ~ 9P~-C~ ought to be of brick, and the larger and higher it is, the strongerthe draft: This may be regulated by a damper as well as by the ash-pit door. The top should be of cast-iron, and the cover roll FIG.. 4. Scale ~-inch to the foot. or slide easily. -~^ ~ 3d. MUFFLE FURNACE FOR SCORIFICATION AND CUPELLATION. Fig. 5 shows Ir Ie sections of a portable cupel furnace. The same furnace may be used for both operations, but generally it will be found convenient to have a larger muffle for scorification and higher heat. The muffles are made of refractory gB,.4__ clay, and in one piece; and should be thoroughly dried before using. FIG. 5. The draft of the furnace ought to be Scale 9-inch to the foot. sufficient to carry off fumes, which are

Page 23 FURNACES AND FUELS. 23 often injurious. The construction of the furnace will vary with the fuel used and work to be done. Fig. 6 shows the vertical and horizontal sections of a double muffle scorification furnace, for works where a large number of S.B-, - - _ scorifications are required. use in the assay!!wk; @@ flerlaboratory of the School of Mines, New York, for two years, and its value has been proved. The muffles are larger than usual, and can be drawn out. D —m ~ — _~ The whole furnace is lined with AdWON'N W W Ifire-brick, as is indicated by the FIG. 6. fine shading. Scale %-inch to the foot. By placing a damper at the top, one-half may be used to the exclusion of the other. THE FUELS employed are coke, anthracite, bituminous coal, and charcoal. Sometimes oil and gas are employed for small laboratory furnaces. The coke should be about egg size and free from sulphur. It is chiefly used in calcining and fusion furnaces. Charcoal, anthracite, and bituminous coal may be employed for the muffle furnace. The latter fuel requiring, however, a special furnace. Anthracite coal, stove size, is best adapted for the assayer's purpose, but charcoal may be used as a substitute for either coke or anthracite, when it can be had more cheaply; it gives a hot fire, and is easily regulated; but requires constant attention, and the pieces used should be of medium size. Various oil and gas furnaces are in use with varying results, but the limits of this work will not permit a description of them. See "Mitchell's Manual of Practical Assaying," pages 71 to 107 inclusive. In lighting a fire it will be often convenient to use pieces of cork or corncobs saturated with rosin, which burn well, are cheap, and save much trouble. To use, it is only necessary to light a piece and lay it upon a little kindling-wood placed in the bottom of the furnace, then put a few pieces of wood on top and add the coal.

The above will have to be corrected from the book. - 1dave

[Admin]

I asked about Cupel sizes on 911 Metalurgest and got the following replys:

Proper crucible Size for 1 A.T. Assay (4 replies)
Dave
2 days ago

In Assaying for Everyone" 1910, p 27.

"The crucible commercially known as Battersea "B" or 20 gram size will be found convenient for use when 1 assay Ton of ore is taken; size "F" or 30 gram when 2 Assay Tons are used, together with the necessary amount of flux."
- J. Reginald Smith
Read more: andy321.proboards.com/thread/77052/assaying-gold-silver?page=1#ixzz4TDNtzIyu

That sounds small for a 20 gram crucible to hold 1A.T. of 29.166 grams pulp + 20 grams lead + reducing agent etc. Is the information correct?
=============================
David
10 hours ago
Like
NEW!

lostsierra usually uses a 30 gram crucible. A 20 gram will work but it will be full. He has also used 40 gram size and use 5AT ton size to do 5AT assays.
=====================
Dave
1 hour ago

Thanks, that is what I suspected - but I don't understand how they went about sizing crucibles. You don't want to fill them more than 3/4 of the way for an accurate assay.

"Assay Crucibles are available in sizes of 30, 40, 50, 55 and 65 grams.

A 30 gram crucible = 4 X 3 X 2 1/8" with a volume of 13.2 Cu.in.
A 40 gram crucible = 5 1/16 X 3 1/8 X 2 1/4" with a volume of 18.6 Cu.in.
A 50 gram crucible = 5 1/4 X 4 X 2.4" with a volume of 23 Cu.in."
What lightweight material did they use for one gram? It must have had a far greater volume than ores and lead.
Read more: andy321.proboards.com/thread/77052/assaying-gold-silver?page=1#ixzz4TOBHQoRn
=====================

David
50 mins ago
Like
NEW!

Capacities given are actual totals, not working capacities. The working capacity is variable and may be from 70% to 90% of those given. The total capacity in pounds of metal depends on the specific gravity and may be found approximately by multiplying the total liquid capacity in pints by the specific gravity of the metal.



I'll leave the rest to an assayer.

[Admin]

When assaying low grade silver ore the resulting buttons can be tiny and hard to weigh. Don't worry. Be happy.
You can just measure the diameter of the button and calculate the weight!

we don't need no stinkin' scales!
"weights of metallic spheres are proportional to the cubes of their diameters"

Plattner and Kleritj came up with ways to make accurate measurements and charts to make final determinations.

[Admin]

fineartamerica.com/shop/greeting+cards/metal+engraving

Assay Laboratory

Assay Laboratory For Gold And Silver

Washing Ore To Extract Gold

Roasting Gold Ore to Recover the Metal

[Admin]

Dec 22, 2016 7:00:20 GMT -7 1dave said:

We could get much more out of using the BLOWPIPE than we do!

Jewelers to the Maharajas of Jaipur and Modern-Day Moguls

EDIT: Replacing lost pictures










Have you ever seen a happier girl?

[Admin]

911 Metallurgist
www.911metallurgist.com/fire-assaying-history/

Fire Assaying History

The beginning history of fire assaying can be traced to the finds in Troy II (about 2600 B.C.) and in the Cappadocian Tablets (2250-1950 B.C.). These finds prove that very pure silver was made in the twenty-fifth century B.C. From this evidence we must conclude that the cupellation process, and therefore fire assaying, was invented in Asia Minor in the first half of the third millennium B.C. shortly after the discovery of the manufacture of lead from galena (Forbes, 1950, p. 213). Theodore A. Wertime (1973, p. 883) wrote that the first convincing evidence of the production of silver from lead ores is the cupel buttons found at Mahmatlar in the late third millenium B.C. and that are now in the Hittite Museum in Ankara, Turkey.

Biblical references to the use of fire-assay techniques can be traced to the prophet Moses (about 1300 B.C.). Numbers 31: 22, 23 states: “Only the gold, and the silver, the brass, the iron, the tin, and the lead, every thing that may abide the fire, ye shall make it go through the fire, and it shall be clean:.” From David (about 1000 B.C.), Psalms 12: 7 (Dahood, 1966 p. 72) states:

“The promises of Yahweh (God)
are promises unalloyed,
silver purged in a crucible,
of clay refined seven times.”

From Solomon (10th century B.C.) Proverbs 17: 3:

“The fining pot [cupel] is for silver
and the furnace for gold:
but the Lord trieth the hearts.”

References to the dross obtained in cupellation are contained in Proverbs 26: 23:

“Burning lips and a wicked heart
are like a potsherd covered with
silver dross.”

From Jeremiah (born after 650, died 570 B.C.) 6: 29 (Bright, 1965 p. 47):

“The bellows blow fiercely,
But the lead comes whole from the fire.
It’s useless to go on refining,
The wicked are not removed.”

Zechariah (sixth century B.C.) 13: 9 states: “And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried:.” More reference is made to the “fining pot” (cupel) in Malachi (fifth century B.C.) 3: 3: “And he shall sit as a refiner and purifier of silver: and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness.”

These references are but a few that demonstrate the extent to which fire-assay techniques permeated Asia Minor in ancient times.

The Romans were able to desilver lead down to 0.01 percent or even to 0.002 percent in some cases and marked their cupelled desilvered lead “EX ARG.” Roman lead pipe was found to be desilvered almost completely. In addition to the employment of fire-assay techniques for refining lead and silver, the Romans were the first to make extensive use of the amalgamation process. This process consisted of mixing the finely ground ore with salt, copper sulfate, and mercury and exposing the mixture to the air in heaps which were constantly worked. The silver-amalgam (silver-mercury compound) was then distilled, the mercury recovered as distillate, and the silver as residue (Forbes, 1950, p. 208). Another version of the amalgamation process used by the Romans in treating rich gold ores consisted of crushing the ore and mixing it with mercury. The gangue was separated by forcing the mercury through leather, and then the amalgam (solution of the gold and silver in the mercury) was heated to recover the noble metals (Forbes, 1964, p. 173). The amalgamation processes were made possible because the Romans produced mercury on a large scale. The ore worked was cinnabar, crushed in sandstone mortars with stone pestles, and heated in furnaces where the mercury distilled off to collect in the fore-hearth.

With the fall of the Roman Empire by the invasions and conquests of the barbarian hordes, intellectual life stagnated for about 500 years. It is doubtful that any significant advancement in the art of fire assaying took place during that period. With the revival of learning in the latter centuries of the Middle Ages, the art of fire assaying was renewed vigorously. One man stands out above all in this period — Agricola (1494 —1555). In about 1529 he began to write “De Re Metallica” (1556), which he completed in 1550 but did not send to the publishers until 1553. Preparation of the woodcuts delayed publication until a year after the death of Agricola. In this book, Agricola, who was the first author to attempt to cover the subject of fire assaying in its entirety, arranged his material systematically. He described the tools and equipment to be used in assaying, stressed the quantitative aspects of each step, and for the first time gave instructions for assaying. “De Re Metallica” was definitely the first and foremost textbook on fire assaying, and it served as a guide to miners and metallurgists for the following 180 years.

Although some publications on fire assaying and metallurgy appeared in the sixteenth and seventeenth centuries following Agricola’s “De Re Metallica,” it was not until the first half of the eighteenth century that creditable works (for instance, C. A. Schluter’s “Hutte-Werken, Braunshweig,” published in 1738, cited by Hoover and Hoover in their translation of Agricola, 1556) began to supersede Agricola’s book. Numerous publications on fire assaying, mining, and metallurgy followed in the 19th and 20th centuries. With continuing worldwide use and interest in the noble metals, one can confidently predict that fire-assay techniques will still be used in the future for the determination of the noble metals.

ia800201.us.archive.org/27/items/georgiusagricola00agririch/georgiusagricola00agririch.pdf

History of Fire Assaying in the US Geological Survey

In 1879, Clarence King, the first Director of the newly-formed U.S. Geological Survey, instructed Samuel F. Emmons, geologist-in-charge, to undertake a detailed study of the geology and mining industry of Leadville, Colo. (Emmons, 1886, p. VII -XI). In 1880 Emmons was fortunate in securing the services of Antony Guyard, a former pupil of the Ecole Des Mines, and, for 12 years, chemist at the well-known metallurgical works of Johnson & Matthey, London. He was assigned to make chemical investigations of the processes of lead smelting used by numerous smelters at Leadville and vicinity.

Thus, in Denver, in 1880 (Emmons, 1886, p. 621) Guyard was the first in the U.S. Geological Survey to use fire assay as an analytical technique. W. F. Hillebrand was also employed in 1880 and, with Guyard, started a chemical laboratory in Denver. Guyard died in 1884. As a result of a general reorganization, Hillebrand was transferred to Washington, D.C., in 1885 (Clarke and Hillebrand, 1897). By 1888 the Survey’s Denver laboratory was closed.

Although Hillebrand’s major interests lay elsewhere, he had become sufficiently familiar with fire assaying and had the equipment necessary to investigate, with E. T. Allen, the special steps needed for fire assaying of gold telluride ores (Hillebrand and Allen, 1905). The results of these investigations remain the basic study for gold telluride analysis. Their experiments, though extensive, suggested the need for additional work. However, the Washington quarters occupied by the Survey had become so crowded that the assay furnaces were dismantled, and assaying was abandoned altogether.

In 1948 there was a need to determine the gold and silver content of samples collected for uranium and thorium investigations, particularly in the Front Range of Colorado. Both the volume of this work and the security requirements of that time made it imperative for the Survey to do its own fire assaying. D. L. Skinner, who had joined the staff of the chemical laboratory in Denver, had had extensive fire-assaying experience at the U.S. Mint in Denver. He supervised the purchase and installation of equipment and in 1951, after an interval of nearly 50 years, revived the use of fire assaying in the U.S. Geological Survey. The furnace was christened by baking a pan of biscuits in it before it was contaminated by lead.

Again, in 1966, investigations for the heavy-metals programs — particularly those concerned with gold and the other noble metals — encouraged the expansion of existing analytical techniques and the search for new ones. Some of the results are given in this manual. One interesting and important result is the combining of fire assaying with such techniques as atomic absorption, optical emission spectrography, and neutron-activation analysis. Thus, in one sense, the very oldest analytical method has been updated by combining it with the most modern techniques.