t0 PHILOSOPHICAL TRANSACTIONS. [aNNO 1757* 



ciety, being since published in the Phil. Trans, renders any recapitulation of the 

 discoveries hitherto made unnecessary. 



The near and remarkable relation between platina and gold, not only in point 

 of gravity, but in many less obvious properties, hitherto supposed to belong to 

 e;old alone ; and their as manifest disagreement in others, particularly colour, 

 ductility, and fusibility ; induced Mr. L. to examine what effects they might 

 have in combination with each other in different proportions; and whether there 

 is reason to credit the report of great frauds having been committed by mixing 

 them together ; how far such abuses are practicable ; and what is of more import- 

 ance, the means by which they are discoverable. 



Experiments on the Mixture of Platina and Gold. 



Exper. 1 . Twelve carats* 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, though 

 defended by a thin coating of pure white clay, had begun to melt. On 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 on the touchstone, of a pale bell-metal colour, without any ' re- 

 semblance to gold. It bore several strokes, and stretched considerably under 

 the hammer, before it began 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 en- 

 tirely 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 6 of platina (= 3 : l) 

 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, though the fusion was 2 or 

 3 times repeated, with the strongest degrees of heat we were capable of exciting 

 by large bellows. 3. Twenty carats of gold and 4 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 l)e 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 2 of platina (= 11 : i) the 



• The proportions were adjusted according to the carat weights, as it is by these that the fineness 

 of gold is usually expressed. A carat is the 24th part of the whole compound : thus gold of so many 

 caiatB, is a composition of which so many 24th8 are fine gold, and the rest of an inferior metal. — Orig. 



