Philosophical transactions, Vol. L. Part I. For the year 1757. · Various
+EXPERIMENT+ I.
1. Twelve carats[56] of fine gold, and the same quantity of the purer grains of platina, were urged in a blast-furnace, for near an hour, with a fire so strong, that a slip of Windsor brick, with which the crucible was covered, tho’ defended by a thin coating of pure white clay, had begun to melt. Upon breaking the vessel, the metal was found in one smooth lump or bead; which, after being nealed by the flame of a lamp, and boiled in alum-water, appeared, both in the mass, and upon the touchstone, of a pale bell-metal colour, without any resemblance to gold. It bore several strokes, and stretched considerably under the hammer, before it begun to crack about the edges. On viewing the fracture with a magnifying glass, the gold and platina appeared unequally mixed; and several small particles of the latter were seen distinct: nor was the mixture intirely uniform after it had again and again been returned to the fire, and suffered many hours of strong fusion. 2. Eighteen carats of gold and six of platina (= 3:1) were melted together as the foregoing, in an intense fire continued about an hour. The bead, nealed and boiled, was less pale-coloured than the former, but had nothing of the colour of gold. It forged tolerably well, like coarse gold. To the naked eye it appeared uniform; but a good magnifier discovered in this, as well as in the other, some inequality of mixture, not withstanding the fusion was two or three times repeated, with the strongest degrees of heat we were capable of exciting by large bellows.
3. Twenty carats of gold and four of platina (= 5:1) were kept in strong fusion for above an hour and a half. These united into an equal mass, in which no granule of platina, or dissimilarity of parts, could be distinguished. The colour was still so dull and pale, that the compound could scarcely be judged by the eye to contain any gold. It hammered well into a pretty thin plate; but we could not draw it into wire of any considerable fineness. 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.
Text from Project Gutenberg, public domain in the United States.