VOL. L.j PHILOSOPHICAL TRANSACTIONS. 90' 



same that standard gold contains of alloy. The mixture was uniform, of a tolera* 

 ble 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 l-i- of platina ( = 15 : 1), melted into a 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 4^ of gold, and 4 of a carat of platina 

 (=31 : 1), formed an equal mixture, very malleable, ductile like the three fore- 

 going while hot as well as cold, but not entirely free from their peculiar dingy 

 colour. 8. A mixture of 23-l. carats of gold, with 4 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. Q. A mixture of 

 23 carats and 4- of gold, with -^ 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 through the gold. The necessity of 

 this precaution appeared from an experiment formerly related: in which one of 

 platina having been melted with 4 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 exteraal, 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. 



Exper. 2. — ^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. All 

 the mixtures proved heavier than standard gold. Their gravities were nearer to 

 the medium of the gravities of the ingredients, than those of the compositions 

 of platina with any of the other metals formerly given an account of; none falling 

 considerably short of the mean gravity, and some rather exceeding it. 



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