PLATING. 
about two inches longer than the tube; a fmall groove is 
made round the cylinder coinciding with the ends of the 
filver tube. Into this groove the ends of the tube are 
clofely worked, fo as to render the fpace between the 
tube and the cylinder perfectly air-tight. The neceflity 
of this will be obvious, fince the whole is required to be 
heated red-hot, which would caufe the oxydation of the 
copper, and prevent the filver from adhering to it. 
When the cylinder and tube are together heated flightly 
red-hot, the fame burniftier that was ufed to unite the 
tube is now rubbed brilkly over the tube in a longitudinal 
direction. This unites the filver firmly to the copper, 
and makes it fit for drawing into wire of various forms 
and fizes. The machinery employed for drawing this 
wire is precifely fimilar to that employed for brafs and 
copper wire. The great variety of figure and form given 
to it depends upon the plate through which it is drawn. 
Some are flat, others half round, Tome fluted, or with 
mouldings. The wire, after drawing, like flieets after 
rolling, is annealed, and afterwards cleaned with hot 
dilute fulphuric acid. 
In forming articles made of wire, fuch as bread-baf- 
kets, toaft-racks, carters, &c. the wire is bent into the 
given form with a wooden block and a mallet. When 
pieces require to be foldered together, the joinings mull 
be accurately fitted, in order to prevent the copper from 
appearing. In thefe cafes hard folder is employed. This 
branch of plated manufadlure admits of extenfive appli¬ 
cation ; as the wires are capable of great .variety of pofi- 
tions. The work lately publifhed by fir James Hall, 
feems to prove that Gothic architecture originated in-the 
fanciful forms of bended twigs. The perufal of this 
work could not fail to give important hints to an inge¬ 
nious manufacturer of plated wire-work. 
All goods formed by hand with the hammer, require 
great labour in finifliing. After hammering the veflel 
into the proper fliape, the marks of the hammer appear like 
fo many flat places. Thefe are removed from the outfide 
of the veflel to the infide, when the inlide is concealed, 
as in tea-urns. This is effected by covering either the 
anvil or the hammer with a piece of the fluff called ever- 
lafting. The roughnefs is transferred to that furface in 
contact with the everlafling. In hammering plated me¬ 
tal from time to time, it requires to be annealed by heat¬ 
ing it red hot : this difeoiours both the filver and the 
copper. Thefe are cleaned by boiling in dilute fulphu¬ 
ric acid, and fcouring with Calais fand. The fulphuric 
acid to the water is in very fmall proportion. If the fil¬ 
ver begins to appear black by boiling, the acid is too 
much, and muff be watered. When the vefiels are 
finifhed in every refpeCt by the maker, and the furface 
free from oxyd, it frequently happens that bits of rolin, 
ufed with foft folder, adhere to it. This is removed by 
boiling in a weak folution of pearl-afhes. The fame is 
alfo ufed for cleaning the furface of tinned copper. 
The greateft improvement ever made in this branch of 
manufacture, is the introduction of filver edges, beads, 
and mouldings. Without this means of defending the 
prominent parts which become fo foon bare in the old 
method, the trade muff long fince have gone into difgrace, 
and ultimately to decay. The filver intended to form 
the prominent and ornamental parts is rolled extremely 
thin, a fuperficial inch fometimes not weighing more than 
ten or twelve grains. 
Plated goods, particularly tea-urns and globular vef- 
fels for the fame purpofe, frequently require to be en¬ 
graved ; but it is obvious that, from the extreme thinnefs 
of the plate, the graver would lay bare the copper; and, 
if the plate were 16 thick all over as to admit of engra¬ 
ving, the articles would be very exper.five. Both thefe 
evils are obviated by working an extra plate of filver 
on to the part to be engraved. This is done while the 
plate, of which the veflel is made, is in its flat form. The 
part where the engraving will fall is firft feraped clean, 
and a plate of filver, of fimilar thicknefs to that employed 
Vol. XX. No. 1396. 
625 
for filver edges, is cut to the fame fize, and alfo feraped 
clean. The plated flreet is then laid upon a hot anvil, 
and the plate of filver laid upon the place prepared. It is 
firft rubbed flowly, but with great preffure, with a po- 
lilhed hammer previotifly heated, but not fo as to affeCl 
the poliflt. The plate will begin to adhere, and it may 
then be flightly hammered; ultimately it will adhere all 
over, and may now be hammered on a poliflied flake, til! 
the whole furface becomes plane, and the piece of filver 
cannot be diftinguiflied from the reft. This procefs is on 
the fame principle as the plating of wire, and is fimilar 
to welding two pieces of iron together. It appears prac¬ 
ticable that the furfaces of any malleable metals, when 
clean and heated to acquire a certain degree of foftnefs, 
are capable of uniting. Mod people are familiar with the 
union of two pieces of lead by preffure, even at the com¬ 
mon temperature. 
When the different plated goods come out of the hands 
of the workmen, the metal, although clean, is of a dull 
white colour, poffefling no polifli whatever. The laft 
finifti, then, is called burnijhing, and is generally per¬ 
formed by females in a diftinft let of apartments. The 
burniftiing-tools are generally made of blood-ftone, and 
fome of hardened fteel finely poliflied. The latter are to 
burnilh the minute parts which cannot be touched by the 
blood-ftone, which is employed chiefly for the greater 
and uninterrupted parts. The bits of blood-ftone are let 
into little cafes, made of flieet iron, and then finely po- 
lifiied. The burnilhers, if ufed dry, would adhere to the 
filver in fome places, and would fcratch inftead of giving 
the fine polifli intended. This is obviated by frequently 
dipping the burnifhing-tool into a folution of white foap. 
After being burnifhed, they are railed, and laftly wiped 
with clean fheep’s leather. 
It is a circumftance much to be regretted, that filver, 
although it is fufceptible of fo fine a polifli, does not keep 
its luftre. This is occafioned by the fulphur which comes 
from fulphurated hydrogen, a gas always exifting in the 
atmofphere. The thinneft coating of any fubftance will 
prevent this change. If the furface of filver were coated 
with a folution of gum arabic or ifinglafs, the defence 
would not be perceived, and the filver would never change 
colour. 
When filver is diffolved in aquafortis, and precipitated 
upon another metal, the procefs is called Jilveriva;, or 
“ walking with filver.” 
PLATI'NUM, f. A metal of which the fpecific gravity 
is fuperior to that of gold. It is indeed the heavielt body 
in nature. 
To our account of this metal under the article Mine¬ 
ralogy, vol. xv. p. 478. it Ihouid be added, that Dr. 
Ingenhoufz found platinum to be as completely, though 
not fo llrongly, magnetic as iron ; and that this power 
was increafed by fulion in eleflrical fire, which he firft ef¬ 
fected, whilft common fire was found to diminifh it. 
This magnetic virtue he conftitutes as a fpecific property 
of platinum, by which it may be always diftinguiflied from 
gold, which cannot be rendered magnetic. This, in fome 
cafes, might ferve perhaps as a tell to deteCt adulterated 
coin; for, as the fpecific gravity of this metal exceeds 
that of gold,it is not eafy, by the eye alone, to diftinguilh 
between a fterling gold coin, fo fmall as a lovereign, and 
a well-executed counterfeit, partly gold and partly pla¬ 
tinum. 
Platinum may now be obtained in plates and in ware, 
and may be worked like gold and filver. There are feve- 
ral ways of purifying this metal. 1. By the magnet, to 
feparate the iron. By waffling, to carry off the fand. 
3. By acids, to feparate the mercury and gold. 
When the platinum is thus brought to the ftate of a 
fait, the next object is to reftore it, thus purified, to its 
metallic ftate, and to confolidate it into a malleable mafs. 
This, from the great infufibility of platinum, has long been 
a matter of confiderable difficulty and labour; and, al¬ 
though the procefs has been, of late years, confiderably 
7 U improved 
