Philosophical transactions, Vol. L. Part I. For the year 1757.: Giving some account of the present undertakings, studies, and labours, of the ingenious, in many considerable parts of the world.Various
History
Philosophical transactions, Vol. L. Part I. For the year 1757.: Giving some account of the present undertakings, studies, and labours, of the ingenious, in many considerable parts of the world.
Various
Science -- Periodicals
4. Twenty-two carats of gold were melted in the same manner with two
of platina (= 11:1) the same that standard gold contains of alloy.
The mixture was uniform, of a tolerable golden colour, but easily
distinguishable from that of standard gold by a dingy bell-metal cast.
It worked well, was forged into a thin plate without cracking, and
drawn into moderately fine wire.
5. Twenty-two carats and a half of gold, and one and a half of platina
(= 15:1), melted into an uniform mass, which, after the usual nealing
and boiling, proved somewhat tougher than the preceding, and of a
better colour.
6. Twenty-three carats of gold were melted with one of platina; which
is nearly half the proportion, that standard gold contains of alloy.
The compound worked extremely well, but was distinguishable from gold
by a manifest dinginess, which it retained after repeated forgings,
fusions, nealings, and boilings.
7. Twenty-three carats and one-fourth of gold, and three-fourths of a
carat of platina (= 31:1), formed an equal mixture, very malleable,
ductile like the three foregoing whilst hot as well as cold, but not
intirely free from their peculiar dingy colour.
8. A mixture of twenty-three carats and a half of gold, with half
a carat of platina (= 47:1), was very soft and flexible, of a good
colour, without any thing of the disagreeable cast, by which all the
foregoing compositions were readily distinguishable, in the mass as
well as on the touchstone, from fine or standard gold.
9. A mixture of twenty-three carats and three-fourths of gold, with
one-fourth of a carat of platina (= 95:1), could not be distinguished
by the eye or hammer from the fine gold itself.
In all these processes, even where the proportion of platina was small,
the fusion was performed by a vehement fire, that the mineral might be
the more intimately dissolved, and equally diffused thro’ the gold.
The necessity of this precaution appeared from an experiment formerly
related; in which one of platina having been melted with four of gold,
the button appeared not much paler than standard gold with silver
alloy. On a second fusion it lost its yellow colour, which had at
first been only external, from an imperfect mixture, great part of the
platina being concealed in the internal part of the mass, and covered
as it were by a golden coat.
The crucibles were rubbed on the inside with chalk, to prevent any
particles of the metal from lodging in their cavities. A little borax
was employed in each as a flux; with the addition of nitre, by which
the colour of gold is somewhat heightened. On remelting some of the
mixtures with sundry other additions, powdered charcoal seemed to
improve the colour most.
+EXPERIMENT+ II.
The preceding compositions, after being gently hammered and boiled,
were weighed hydrostatically with great care, by a very tender balance,
in distilled water, wherein the gravity of standard gold turned out
17.788.
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