634 GEOLOGY AND MINING INDUSTRY Oi LEADYILLE. 



avoirdupois, or to 29, ICG oiiuces troy, or to 907,180,000 millisrams. The weight of the 

 assay ton is 29,l«G milligrams, cousequeutly each milligram rcpreseuts oae ounce troy, 

 and 29,1GG milligrams represent oue 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 

 iu milligrams, or multiples of the milligram, correspoudiug to those of the assay ton, 

 expresses iu troy ounces the weight of gold or silver contained iu 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 oue 

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

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



2. One-half an assay tou of slags gives, after assayiug, a button weighing IJ 

 milligrams; this shows that oue tou of slag contains 3 ounces troy of silver. 



3. Oue-teuth of an assay ton of ore contains 3 milligrams of silver; this 

 shows that one tou 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 iu assaying by the wet way. Iron and 

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

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



Silver assays The geueral process used by common cousent iu Leadville for ore 



assays is the scoritication process, a rapid aud accurate method. Some mines, however, 

 require crucible assays. The scoriflcation process is so well kuown aud so fully de- 

 scribed iu text books that it will not be insisted upon. The assays of each sample are 

 made iu three or four scorifiers. One tenth of an assay tou is weighed for each scorifler, 

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

 rather with a granulated lead whose contents iu silver are known aud subsequently 

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

 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 aud other bases. Slag, like 

 ores, is assayed by scoriflcation ; but this process ought to be abandoned aud the 

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

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

 the estimation of 1 or IJ 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 i assay ton. 



Litharge - 1 assay ton. 



Bicarbonate of soda * assay tou. 



Borax i assay ton. 



Arsol -,- u) assay ton, 



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

 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 geuei-ally made on a car-load ,'-ami)le, representing 



10 tons. Two pieces of lead are detached from the top aud bottom i)art of each bar 

 of bullion forming the carload (in geueral 400 bars); all these are melted together in 

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

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



