124 



On some Combinations of Platinum. By Edmund Davy, Esq. Pro- 

 fessor of Chemistry, and Secretary to the Cork Institution. Com- 

 municated by F. Babington, M.D. F.R.S. Read February 17, 

 1820. [Phil. Trans. 1820, p. 108.] 



The principal object of this paper is to describe a peculiar com- 

 pound of platinum, obtained from the sulphate by the agency of al- 

 cohol. On boiling sulphate of platinum with alcohol, a substance is 

 precipitated, which, when dried, is black, insoluble in water, and un- 

 alterable by exposure to air. It is reduced with a slight explosion 

 when heated. It acquires fulminating properties when steeped in 

 ammonia. It is insoluble in nitric, sulphuric, and phosphoric acids, 

 and slowly soluble in muriatic acid. By alcohol it is immediately 

 decomposed, as shown by slightly moistening it with that liquid ; 

 and such heat is produced as to ignite the separated platina. During 

 these changes acetic acid is formed. 



Mr. Davy gives a detailed analysis of this powder, whence it ap- 

 pears to consist almost solely of platinum, with a little oxygen, and 

 the elements of nitrous acid ; a small portion of carbon was also ob- 

 tained, which, however, the author regards as accidental; the presence 

 of nitrous acid is referred to the manner in which the sulphate of pla- 

 tinum is formed, namely, by the agency of nitrous acid on sulphuret 

 of platinum. 



In the fifth and sixth sections of this paper, Mr. Davy describes 

 the action of sulphate of platinum upon solutions of jelly, in which 

 it forms a precipitate composed, when dried at 212, of 

 56' 11 oxide of platinum, 

 20' 02 sulphuric acid, 

 23'87 gelatine and water. 



The author considers the sulphate of platinum as the most delicate 

 known test for jelly. 



In the seventh section of his paper, Mr. Davy describes a grey ox- 

 ide of platinum, obtained by the action of nitrous acid on fulminating 

 platinum, and affording on analysis, 



100 platinum + 11 '9 oxygen. 



Assuming, with Vauquelin and Berzelius, that the black oxide of 

 platinum contains 15 per cent, of oxygen, the author observes that 

 the grey oxide which he has described may be considered as the pro- 

 toxide, and will consist of one proportion of platinum and one of 

 oxygen, or 126 platinum + 15 oxygen, and the black oxide will 

 consist of 126 platinum and 22'5 oxygen, or of one proportion of 

 metal and 1^ of oxygen. 



On the Methods of Cutting Rock Crystal for Micrometers. By Wil- 

 liam Hyde Wollaston, M.D. F.R.S. Read February 24, 1820. 

 \Phil. Trans. 1820, p. 126.] 



For the purpose of examining the phenomenon of double refrac- 

 tion, it is easy to combine a wedge of rock crystal with one of crown 



