TIN

TIN

t 4I(J )

i'ubje& to confulerable variation: the lighter isits colour and the greater is the proportion ofthis metal. A fpecimen of this kind was com-pofed, according to an analyfis by Klaproth ,of 34 Tin

36 Copper25 Sulphur2 Iron

97

It has hitherto been found only at WhealRoch, in the parifh of St. Agnes in Cornwall ,in a vein about nine feet wide, accompanied byblende and copper pyrites.

§ 2. Affay and Analsfts.

The affay of tin ore is extremely fimple.Being firft reduced by pounding to the confid-ence of coarfe fand, it is feparated by wafhingfro'm the dony matters with which it is mixed(a procefs that may be performed with greataccuracy on account of the high fpecific gravityof the ore). A grain or two is then to betreated by the blowpipe in order to afcertainwhether any arfenic is prefent. If this is thecafe, 200 grains of the ore mixed with a littlecharcoal, are roaded in a calcining ted at alow red heat, till no arfenical vapours areany longer to be perceived; the refidue beingwithdrawn from the fire is to be mixed with alittle pitch and fine faw-dud, and put into acrucible lined with charcoal; a cover beingluted on, it is to be placed in a wind or forgefurnace (the latter is the bed) and pretty ra-pidly raifed to a bright red heat: in a quarterof an hour or twenty minutes the reductionwill be compleated, the crucible being then re-moved from the fire and cooled, there will befound in it a button of metallic tin, either en-tirely free from fcorire, or at mod covered witha very thin blackilh crud, which may be re-moved by gentle hammering.

if the ore on trial with the blowpipe appearto be entirely, free from arfenic, the readingmay be omitted.

The analyfis in the moid way though fome-what' more complicated, is yet upon the wholeiufficiently fimple. The method attempted byBergman and others, of analyfing the ores of tinby means of acids, is extremely unfatisfaeftory,little or nothing but the impurities being takenup by thefe mendrua. The proper mode oftreating thefe ores is by means of the fixed al-kalies; 1 ’ the difeovery of which forms one of

the numerous obligations conferred by Klaproth on analytical chemidry.

Tinflone.

Specimens of this mineral from Cornwall andBohemia were thus analyfed by Klaproth .

(a) 100 grs. in crydals were ground to a finepowder, and added to a lixivium containing 60 ogrs. of caudic potafh. This mixture was eva-porated, and then moderately ignited for halfan hour in a filver crucible ; a greyifh-whitemafs was thus obtained, to which, while yetwarm, was added boiling water, which diflolvedthe whole with the exception of n grs.

( b ) Thefe 11 grs. were again ignited with fixtimes their weight of caudic potafh, and beingdigeded in boiling water there remained behindonly 1 1 gr. of a fine yellowilh-grey powder.

( c ) The alkaline dilutions being mixed to-gether, muriatic acid was added to faturation,upon which a white oxyd of tin fell down : thiswas rediffolved by an excefs of muriatic acid,and finally precipitated by carbonated foda.This precipitate when wafhed and dried at agentle heat, appeared in the form of tranfpa-rent yellowifh lumps, with a vitreous fracture.

(d) This precipitate being pulverized wasdidolved in muriatic acid, and into the dilution,previoufly diluted with two or three parts ofwater, was inferted a ftick of zinc, by whichthe tin was thrown down in the form of thinmetallic laminae. Thefe being wafhed and driedwere fufed in a fmall crucible under a cover ofmelted tallow, and afforded a metallic buttonweighing 77 grs.

(i e ) The refidue of b amounting to i| gr. wastreated with muriatic acid, with which it form-ed a yellowifh folution : from this 0.5 gr. oftin was feparated by means of zinc. The re-mainder afforded a light blue precipitate withpruffiat of potafh, indicating not more than0.25 gr. of oxyd of iron : about 0.75 gr. offilex was alfo procured. By adding thefe pro-duces together, and making no allowance forlofs, there will remain 21.5 grs. for the oxy-gen contained in the ore.

Wood-Tin is to be analyfed in the fame man-ner as the preceding.

Bell Metal Ore .

This was treated by Klaproth in the follow-ing manner.

(a) 120 grs. being reduced to a fine powder,were digefted in the cold for 24 hours withaqua regia, compofed of two parts muriaticand one part nitric acids : the mixture wasthen digefted for fome time longer on a fand

k Klapr. Analyf. Vol. I. p. 511.