combination with silicic acid, 100 milligrammes of the substance should be dressed with

by which the silicic acid combines with soda, and the oxide of tin is reduced. But as oxide of lead is often present in enamel, and is also very easily reduced, the resulting tin will not be pure, owing to its combining with a portion of lead. Such a compound cannot be separated into its elements in the dry way, but with nitric acid the lead can be dissolved out, leaving the tin as oxide undissolved. It is then only necessary to edulcorate this oxide, dry it, ignite it strongly in a platinum spoon, and calculate the value of metal from the weight of the ignited oxide,-100 parts of oxide of tin containing 78.62 parts of metallic tin.

C. DETERMINATION OF TIN IN STANNIFEROUS ALLOYS.

To this class belong bell and gun metal, and all combinations of tin with lead, bismuth, zinc, and antimony. But as the quantitative determination of tin in the latter compounds in the dry way, with the Blowpipe, is very uncertain, while in the moist way, on the other hand, it may be easily and accurately determined, the application of the Blowpipe is therefore confined to bell and gun metal, which are compounds of tin with copper.

The method of separating tin from copper has been already fully described, in speaking of the Copper Assay at page 360. In this method, the copper is the principal object of investigation, no reference being made to the tin. But if it is required to find the value of tin at the same time, the glass which contains the whole of the tin as oxide should not be lost, because the metal may be again reduced from it.

When desirable to determine the tin before the Blowpipe, in a combination of tin and copper, the tin must be oxidized by the method previously described, and in this state separated, together with the flux, consisting of soda, borax, and silica. This glass should then be pulverized, mixed with about 50 milligrammes of

soda, this mixture introduced into a soda paper cornet, and fused, surrounded with charcoal, between two pipe-clay capsules, like an ordinary tin assay. But the tin But the tin is found, after the fusion, contaminated with a trace of copper, owing to an exceedingly small quantity of the latter combining with the glass in this operation.

The resulting tin is now to be weighed, and the centesimal value found by calculation, as only 50 milligrammes of such metallic compounds are generally employed in an assay.

APPENDIX.

C C

SYSTEMATIC ARRANGEMENT

OF THE

OXIDIZED MINERALS,

ACCORDING TO THEIR BEHAVIOR BEFORE THE BLOWPIPE.

for

WHEN the nature of a mineral is to be ascertained by its behavior before the Blowpipe, the external characters not being sufficiently distinct for that purpose, it is important, especially young mineralogists, that some arrangement should be contrived, by which the number of species, with which the mineral under examination is to be compared, should be diminished, so as to be as small as possible. Such a systematic arrangement, which, although deficient in many respects, will not be without use, is now given. Three properties of minerals; namely, fusibility, intumescence, and behavior with soda, have been especially considered. The principal divisions depend on the former two properties, the subdivisions on the latter.