42 TIN DEPOSITS OF THE YORK REGION, ALASKA. [no. 229. 
with gangue minerals, must be concentrated. Without such treatment 
it is impossible to obtain even an approximate estimation by the dry 
method usually employed, and in an ore containing less than 10 per 
cent it is probably impossible to obtain any tin at all. A study of the 
literature regarding tin analyses has convinced the writer that the 
reports of dry assays of low-grade tin ores, in which the cassiterite can 
not be recognized by the naked eye or separated by hand panning, are 
of no value. 
For assaying a the ore is first pulverized and screened to uniform 
size, care being taken in the crushing to prevent the formation of 
slimes, since cassiterite is very brittle. The pulp is then roasted in 
a muffle to decompose any sulphides and arsenides that may be present. 
After roasting, and while still hot, it is thrown into cold water, which 
finely subdivides the ore and exposes a much larger surface to the 
action of acids. The ore is then boiled with nitrohydro-chloric acid 
to remove all soluble metallic compounds. This boiling must be con- 
tinued until iron censes lo dissolve. The ore is then washed with hot 
water, transferred to a gold pan. and washed free from visible impu- 
rities. The ore thus prepared for assay may be treated by either of 
the two following methods, the first being preferred: 
The finely pulverized ore is mixed with live times its weight of chemically pure 
potassium cyanide, then fused in a clay crucible in a bright fire. A steady fusion is 
kept up for from 10 to 15 minutes at the highest point to winch potassium cyanide 
can be heated without showing heavy fumes. 
Five grams of KCN are rammed into the bottom of the crucible. The charge, con- 
sisting of 10 grams of ore mixed with ft) grams of potassium cyanide, is then poured 
into the crucible, and 5 grams of KCN placed on top of the charge. 
A "G" Battersea or Denver crucible may be used for pot-furnace work, and a 
"B" or 20-gram Colorado crucible will probably do for muffle work. 
The following charge is said to be taken from Kerl and Balling/' 
Five grams of ore are intimately mixed with 0.75 to 1 gram of charcoal dust and 
charged into a clay crucible. On top are placed 12.5 to 15 grams black flux <' (or 
substitute) with 1 to 1.25 grams borax glass, then a salt cover, and finally a piece of 
charcoal. The crucible is covered, heated in a muffle or a pot furnace at a moderate 
gradually increasing temperature until the boiling has ceased, and then from one- 
half to three-fourths of an hour at a white heat. The crucible is removed from the 
fire, broken when cool, and the tin button weighed. 
The salt cover should be about one-fourth inch thick. It would seem 
that finer charcoal would cover the charge as well as a single piece, 
for the object is to keep the charge in a reducing atmosphere. These 
methods are found to give within 0.5 per cent of the results of wet 
assays when used with well-cleaned minerals. 
aHofman, H. 0., The dry assay of tin ores: Trans. Am. Inst. Min. Eng., vol. 18, 1890, pp. 3-54. 
& Kerl, Metallurgische Probirkunst, Leipzig, 1882, p. 412. Balling, Die Probirkunde, Brunswick, 
1879, p. 391. 
c Black flux is 1 part niter (KN0 3 ) and 3 parts argol, deflagrated. Black flux substitute is 2 parts 
potassium carbonate or sodium bicarbonate and 1 part flour. 
