634 GEOLOGY AND MINING INDUSTRY Ol LEADV1LLE. 



avoirdupois, or to 29,166 ounces troy, or to 907,180,000 milligrams. The weight of the 

 assay ton is 29,166 milligrams, consequently each milligram represents one ounce troy, 

 and 29,166 milligrams represent one ton. When the material to be assayed for precious 

 metals is weighed by the assay ton or its multiples, the weight of the precious metals 

 in milligrams, or multiples of the milligram, corresponding to those of the assay ton, 

 expresses in troy ounces the weight of gold or silver contained in one ton of ore or 

 bullion. A few examples will illustrate this : 



1. Twenty-nine thousand one hundred and sixty-six milligrams of bullion, or one 

 assay ton, give after cupellation a button of silver weighing 205.5 milligrams. This 

 shows that one ton of this bullion contains 205.5 ounces troy of silver. 



2. One-half an assay ton of slags gives, after assaying, a button weighing 1 

 milligrams; this shows that one ton of slag contains 3 ounces troy of silver. 



3. One-tenth of an assay ton of ore contains 3 milligrams of silver; this 

 shows that one ton of ore assays 30 ounces troy of silver. 



The laboratories are provided also with sand-baths, flasks, beakers, dishes, bu- 

 rettes, and a few of the principal reagents used in assaying by the wet way. Iron and 

 gangue assays are regularly made in the wet way, and occasionally the ore is assayed 

 for sulphur and arsenic, the slags for lead, the ores and fluxes for lime and magnesia. 



Silver assays The general process used by common consent in Leadville for ore 

 assays is the scorincation process, a rapid and accurate method. Some mines, however, 

 require crucible assays. The scorincation process is so well known and so fully de- 

 scribed in text books that it will not be insisted upon. The assay* of each sample are 

 made in three or four scorifiers. One tenth of an ass;iy ton is weighed for each scorilier, 

 and then mixed with ten times its weight, or one assay ton, of pure granulated lead, or 

 rather with a granulated lead whose contents in silver are known and subsequently 

 subtracted from the silver buttons obtained. The silver-prills are weighed to the tenth 

 of a milligram, and each of these divisions corresponds to an ounce to the ton. A 

 little borax is always used to scorify the oxide of iron and other bases. Slag, like 

 ores, is assayed by scoriflcatiou ; but this process ought to be abandoned and the 

 crucible process substituted for it, chiefly for the reason that in the crucible the assay 

 may be made with one assay ton if necessary, this quantity not being excessive for 

 the estimation of 1 or 1 ounces of silver to the ton. The crucibles used in crucible 

 assays are those drawn to scale in Figs. 3 and 5, Plate XLIII. A mixture of 



Powdered ore $ assay ton. 



Litharge 1 assay ton. 



Bicarbonate of soda A assay ton. 



Borax i assay ton. 



Argol iV assay ton, 



or some similar mixture, for each assayer has his favorite flux, is fused in them, 

 in the presence of an iron nail or rod, which, however, some assayers dispense with 

 altogether. The mixture is generally covered with a layer of borax or common salt. 

 Bullion assays The assays are generally made on a car-load s-arnple, representing 

 10 tons. Two pieces of lead are detached from the top and bottom part of each bar 

 of bullion forming the car-load (in general 400 bars); all these are melted together in 

 a plumbago crucible, under a cover of live charcoal; the charcoal and scum are then 

 removed; the sample, well mixed by stirring, is poured into an ingot mold (a bullion 



