MANUFACTURES.
417
Manufac-
tures.
Specificgravity of
and for this purpose is to be raised upon an earthenstand about 24 inches above the grate of the furnace,the stand being strown over with a layer of clean quartz-ose sand, on which the cake is to be placed, standingupright on one of its ends. It is then to be covered withan inverted cylindrical pot, of the most refractory cru-cible ware, resting at its open end upon the layer ofsand, and care is to be taken that the sides of the potdo not touch the cake.
“ To prevent the blistering of the platina by heat,which is the usual defect of this metal in its manufac-tured state, it is essential to expose the cake to the mostintense heat that a wind furnace can be made to receive,more intense than the platina can well be required tobear under any subsequent treatment, so that all im-purities may be totally driven off, which any lower tem-perature might otherwise render volatile. The furnaceis to be fed with Staffordshire coke, and the action ofthe fire is to be continued for about twenty minutesfrom the time of lighting it, a breathing heat being main-tained during the last four or five minutes.
“ The cake is now to be removed from the furnace,and, being placed upright upon an anvil, is to be struck,while hot, on the top, with a heavy hammer, so as atone beating effectually to close the metal. If in thisprocess of forging the cylinder should become bent, itshould on no account be hammered on the side, bywhich treatment it would be cracked irremediably; butmust be straightened by blows upon the extremities dex-terously directed, so as to reduce to a straight line the
Parts which project.
“ The work of the operator is now so far complete,that the ingot of platina may be reduced, by the pro-cesses of heating and forging, like that of any othermetal, to any form that may be required. After forging,the ingot is to be cleaned from the ferruginous scales,which its surface is apt to contract in the fire, by smear-mg over its surface with a moistened mixture of equalParts, by measure, of crystallized borax and common salt°f tartar, which, when in fusion, is a ready solvent ofs ueh impurities, and then exposing it, upon a platinaj£ a y, under an inverted pot, to the heat of a wind furnace.The ingot, on being taken out of the furnace, is imme-diately to be plunged into dilute sulphuric acid, which1? *he course of a few hours will entirely dissolve the? ux adhering to the surface. The ingot may then beflattened into the leaf, drawn into wire, or submitted toan y processes of which the most ductile metals areCa pable.
The perfection of the methods above described forS‘ v ' n S to platina complete malleability, will best be esti-oHt ^ . com paring the metal thus obtained, in respects specific gravity, with platina which has undergone. P.® te fusion ; and by comparing it, in respect of itsn , 1 Wl *h other metals possessing that quality in the.fqf 1 P erf eetion.
from u s P ec *fm gravity of platina, drawn into fine wirelate D p t0n ’ w ^' c f 1 had been completely fused by theIf j Clarke with an oxyhydrogen blowpipe,
fh e ° Un , he 21.16. The aggregate specific gravity ofbarrM 6 i n ? eta H* c mud, when first introduced into thefrom exa usively 0 f moisture, is about 4.3 ; when takencontract rl ress > isabout 10 ; that to which the cake fullyforo-i 6 ’ on using taken out of the wind furnace before
of the^pllttoTaft ‘V™' The , mean s P ecific § mvit ythat nf er fu r 8' ln g is about 21.25, although
me rods after being drawn is 21.4 ; but that
of fine platina wire, determined by comparing the weight Mechanicalof a given length of it with the weight of an equal Processes,length of gold wire drawn through the same hole, I.find to be 21.5 ; which is the maximum specific gravitythat we can well expect to be given to platina.
“ The mean tenacity, determined by the weights re- Tenacity ofquired to break them, of two fine platina wires, the one the wire,of ■jg-Vo' the other of -g-gj-jj of an inch in diameter, re-duced to the standard of a wire T * c th of an inch in diame-ter, I found to be 409 pounds; and the mean tenacityof 11 wires, beginning with and ending with
crihny °f an inch, reduced to the former standard, Ifound to be 589 pounds; the maximum of these 11cases being 645 pounds, and the minimum 460 pounds.
The coarsest and the finest wire which I tried presentexceptions; since a wire of of an inch gave 290
pounds, and a wire of a-o-rinr of an inch, 190 pounds.
If we take 590 pounds, as determined by 11 consecutivetrials, to be the measure of the tenacity of the platinaprepared by the processes above described, and considerthat the tenacity of gold wire, reduced to the same stand-ard, is about 500, and that of iron wire 600 we shallhave full reason to be satisfied with the processes de-tailed in the present Paper , by which platina has beenrendered malleable.”— Phil. Trans, for 1829.
(594.) This compound metal was known to the Ancients, History ofas we find by many parts of the Old Testament , as well as brass,from various ancient Historians, but it does not appearthat they were properly acquainted with its nature orcomposition. They considered it as 'a particular kind ofcopper, found native in the mines in which zinc andcopper seem to have been found in the proper propor-tions for its production: it was denominated by theGreeks Orichalcum , i. e. Ms montanum, a particularsort. Ms Corinthiacum is generally supposed to havebeen a mixture of gold, silver, and copper, metals withwhich Corinth abounded, melted down together at theburning of this city by the Romans in a. c. 496. Atwhat time the actual constitution of brass became known,is not stated with any certainty, but it appears un-questionable, that in early times it was exceedinglyvaluable, from the supposition of its being a rare anddistinct metal, or particular species of copper; it beingstated that as the mine in which it was obtained failed, itwas supposed to be impossible to obtain it any otherway, and that in value it held a middle place betweengold and silver.
After the real nature of brass became known in Europe ,the Art of making it was principally confined to Germany ,where the processes were kept very secret; and the firstbrass made in England was by persons of that nation,
Jacob Momma and Daniel Demetrius, who, about theyear 1649, established a brass work at Esher in Surrey ,at a cost of £6000, but not meeting with encouragement,they were ruined by their undertaking, and the workswere discontinued. Others, however, were afterwardsestablished, and the operators employed English ore ofzinc, which had been hitherto transported merely asballast, but the copper was imported from Sweden till therevival of our own coppei works in 1690.
The ore of zinc which is used in combination with cop- Ores °fper to constitute brass, is called by the English calamine; it zinc > theiris of various colours, most commonly greyish with a cast coluur » &t ‘of brown, a yellowish.arid a pale red. Some pieces are of