METHODS OF TIN MINING. 53 
mestion is ground to a very fine powder between two clean pieces of steel (the face of a ham- 
ner and a shovel will serve), it may generally be safely rejected as not containing tin if the 
>owder is black. If brown or still lighter in color, recourse may be had to the blowpipe test, 
vhich is applied as follows: So much of the finely ground material as can be piled on an area 
►ne-fourth inch square is added to twice its bulk of powdered charcoal and to three times its 
>ulk of pulverized sodium carbonate, or ordinary washing soda. These three substances are 
horoughly mixed and then transferred to a little depression in a stick of charcoal, where they 
ire moistened to a thick paste. The flame of an alcohol lamp is then directed upon them 
nth a blowpipe, care being taken to envelop in the flame as much of the material as possible 
ind at the same time to produce an intense heat. If the operation is properly carried out, 
he presence of tin will be indicated by the appearance of small globules, which seem darker 
>r less highly heated than the surrounding material. By continued heating numbers of 
hese particles can be made to coalesce into a bead of appreciable size. The formation of 
uch metallic beads or globules is not, however, a proof of tin, but may be due to the pres- 
mce of any one of a group of metals of which tin is a member. On being removed from the 
lame the globules often become oxidized on the surface and covered with a white layer 
vhich masks their metallic character; but if the melted mass is crushed after cooling the 
lattened pieces of metal may readily be observed. If a white insoluble residue results when 
he metallic beads are treated with concentrated nitric acid, it may be considered that tin is 
>resent. 
EXTRACTION. 
The typical tin ore of this region — that is, the unaltered pegmatite containing tin — must 
>e crushed to obtain the tin mineral. Ledoux tried stamping, and erected a 10-stamp mill 
or his operations. He was met by two difficulties, however. The large foils of mica, being 
ough and elastic, resisted comminution and gave trouble by clogging up the screens and the 
nortars, and the heavy impact of the stamps served to crush the brittle cassiterite so fine 
hat much of it could not be saved in the subsequent concentration operations. Since that 
ime stamping has not been attempted. 
The equipment of the Jones mill is supposed to be sufficient to handle 100 tons of ordinary 
naterial per day. Besides boiler and engine, the machinery consists of a jaw crusher, rolls, 
slevators, screens, a pair of mechanical two-compartment jigs, and a Bartlett table. The 
irrangement appears well adapted for economical handling. 
Coming from the mine the ore passes through the crusher and goes to a revolving screen, 
vhere it is divided into eighth-inch and half-inch sizes. The smaller size goes to the concen- 
rating table and the larger goes to the jigs, while the oversize goes to the rolls and then again 
hrough the screen. Considerable trouble has been experienced with the crushing machin- 
ery. The mica binds the rock together and makes it tough and springy, so that the crusher 
s continually being choked. When a stream of water is directed into the crusher the diffi- 
culty is slightly lessened, but clogging can be prevented only by frequent prodding with a 
>ar. It is probable that the harder ore now being reached in the lower part of the mine will 
jive less annoyance. The rolls are also subject to the same difficulties, but by the use of an 
abundance of water they can be kept ahead of the crusher. It is thought by Mr. Seamon, 
>resident and general manager of the company, that sluicing of the ore as it comes from the 
nine will remove a large amount of the mica and thus increase the capacity of the crushing 
naehinery. This can be demonstrated only by experiment. It is believed that the best 
emedy would be the substitution of a rotary crusher for the jaw crusher now being used. 
he jigs make a very good product, although it is probable that an appreciable amount is 
t by attrition, as the grains removed from the upper compartment are in all cases worn 
nd rounded. It may be found advantageous to take some steps to save the fine material 
ow carried away. Possibly a trap in the broad launder which carries off the tailings would 
ccomplish this end. 
To produce a clean concentrate it is necessary to run the material twice over the table. It 
i intended to reduce the size of the smaller screen and thus give the table a narrower range 
