TIN

TIN

( 417 )

"bath. When the acid had entirely ceafed toaft, the iolution was dilated with water andfiltered ; 43 grs. remained undiffolved, ’fromwhich by gentle ignition on a teft there werefeparated 30 grains of fulphur. The refidue,amounting to 13 grs. was digested in nitro-muriatic acid, by which 8 grs. were taken up.The remaining 5 grs. confifted of about 3 grs.of filex, and 1 gr. of iron, reduced to the ftateof magnetic oxyd by roafling with wax.

b. The acid folutions being mixed together,carbonat of potafh was added to faturation, bywhich there was obtained a dirty-green precipi-tate, which by fubfequent folution in muriaticacid afforded a green fluid. A cylinder of puretin weighing 217 grs. was immerfed into thefolution till it became quite colourlefs, in con-fequence of the precipitation of 44 grains ofreguline copper.

c. This copper by briflc digeftion in nitricacid left behind a little white oxyd equivalentto 1 grain of tin ; hence the true amount ofcopper is equal to 43 grs.

d. The cylinder of tin during its digeftion inthe folution b, had loft 89 grs. This folutionwas now decompofed by a cylinder of zinc, andthe metallic precipitate when waflied and driedwas mixed with tallow and charcoal powder,and moderately heated in a crucible; therewere thus obtained, 1 gr. of magnetic oxyd ofiron and 129 grs. of reguline tin, front whichdeducting 89 grs. as belonging to the cylinder,there remain 30 grs. for the amount of tin inthe ore.

j. 3. Reduclion of Ores.

The method of treating the ores of tin inCornwall is two-fold. c The firft that we fltallmention is that to which the tinftone from themines or vein-tin is fubjefted; the fecond is thatby which the dream tin is reduced.

r. The vein-tin is procured by Mailing, andwhen brought to the top of the pit is in frag-ments of various fizes, and mixed fo largelywith .quartz, argillaceous fchiftus, granite, andother impurities as rarely to contain more than2 per cent, of metal. The firft preparationthat it receives is being broken by hand ham-mers into pieces about the fize of hens’ eggs,after which it is ready to be itamped. Theftamping-mill is of the ufual conftruftion (feethe article Gold) except that the dampers areonly tnree in number, and in front of thetrough or coffer there is inferted a plate of tinabout a foot fquare, pierced full of holes, largeenough to admit a moderate fized knitting-

needle; that furface of the plates which is oc-cupied by the rough extremities of the holes isplaced on the infide of the trough, by whichAmple and effeftual contrivance the holes areprevented from being plugged up by the ore.In proportion as the tin-flone is reduced to theproper degree of finenefs it pafles with thewater through thefe holes into a labyrinth ofvery Ample conftruftion; here the oxyd of tinis feparated from much of the lighter impuri-ties, and by fubfequent wafhing on a woodentable it is fufficiently drefled to be fent to theroafting furnace; in this ftate it is called blacktin , and is generally mixed inconfiderable propor-tion with mifpickel, and iron and copper pyrites.It is now calcined at a low red heat in a largereverberatory furnace for feveral hours in orderto volatilize the arfenic and bum off the ful-phur, (a part of this laft after being acidified,combines with the oxyds of copper and iron).The ore comes out of the roafting furnace of abright ochery red colour, owing to the decom-pofition and oxydation of the pyrites.and mif-pickel, the oxyd of tin, if the operation hasbeen well performed having undergone not theleaft alteration. The ore is now waflied a ie-cond time, by which nearly the whole of theimpurities are feparated. The water employedin this procefs being confiderably impregnatedwith fulphat of copper is referved, and after-wards decompofed by the addition of pieces ofold iron. The next ftep is the reduftion, pro-perly fpeaking; for this purpofe a reverberatoryfurnace, about 7 feet long and 3! feet wide, ischarged with 7 cwt. of roafted ore mixed with■j- of its btdk of culm (Welch fmall-coal) nolime or any other kind of flux being made ufsof; the fire is kept up pretty briflc for about fixhours, and the tin in proportion as it is reducedfinks down to the bed of the furnace, being co-vered with a boiling hot bath of black fcorias.At the expiration of this period the furnace istapped by means of an iron bar, and the hotmetal flows into a {hallow pit at the foot of thefurnace. When the whole of the metal hasrun out, the fcorite are drawn out of the furnacewith a rake, and a frefli charge is immediatelythrown in. While the metal in the pit is redhot it throws up a quantity of flag very rich inmetal, which is immediately returned into thefurnace, and the melted tin after it has becomefufficiently cool is taken out with iron ladlesand poured into moulds of granite, where itconfoiidates, each charge affording on asaverage from 4 to 5 cwt. of metal. The firft

Original Communication.

T-OL. H.