INTERESTING CRYSTALLINE ALLOTS. 81 



My next experiment was to remelt some of the original Bi 

 compound with. Ag, so arranging that the Ag should exist in the 

 melted alloy in the proportion of one atom of Au to one of Ag. 

 The alloy was prepared by melting in a small crucible under a 

 layer of borax, and then allowing the crucible, with its contents, 

 to cool very slowly. This was done by placing the small cruci- 

 ble inside a larger crucible that had been previously made red- 

 hot, and allowing the whole thing to stand until cold. The small 

 crucible was then broken and the button of alloy detached. This 

 alloy was found to be very brittle and crystalline. It was broken 

 into lumps and treated in a flask with dilute nitric acid — one of 

 acid to three of water. I found, after all the Bi had been attacked 

 by the acid, that nothing was left behind but a beautiful crystal- 

 line alloy of Au and Ag (No. 4). There was an entire absence of 

 any Bi Au compound, which was found in former experiments. 

 The solution of nitrate of Bi showed no trace of Ag. These crystals 

 were found to contain : Gold, 62.164 per cent.; silver, 35.486 

 per cent.; Cu and Bi, 2.35 per cent. Further boiling of the 

 crystals with strong nitric acid gave (No. 5) : G-old, 65.21 ; silver 

 33.19; copper, 1.60. 



Alloys of gold and silver in all proportions may be obtained 

 in this way, depending on the amount of Ag used and also on 

 the strength of nitric acid employed in the separation of the Bi. 

 The largest and best formed crystals are, however, those in 

 which the Au and Ag exist in the ratio of their atomic weights. 

 Repeated boiling with strong nitric acid wiU, however, remove a 

 portion of the Ag, without in any way damaging the crystals or 

 effecting any very marked change in the color. In a number of 

 experiments that I have made with the alloys of Au and Ag, the 

 lowest percentage of Au resulting from treatment with HNOg was 

 58.51 (No. 6), and the highest 94.15 (No. 7). 



Alloys of Gold and Copper. 



Crystals of an allo}^ of Au and Cu may be obtained precisely 

 in the same way by substituting Cu for Ag. The form of 

 crystals is the same, that of the regular octahedron, but they 

 are much smaller. A crop of crystals was obtained having the 

 composition 61.52 Au and 38.48 Cu (No. 8). On treating these 

 crystals with strong nitric acid and boiling for some time until 



