EXPERIMENTS ON PLATINA. 6.5 



«Tcamined tbe state of my solution, and I saw, that it still 

 reddened litmus paper perceptibly ; and if I added a small 

 portion of acid, the precipitate produced in it by sulphuret- 

 ted hidrogen was no longer black, but of a tine yellow. 



Thus it appears to me demonstrated, that when the ni- A predomi- 

 tric acid is in too small proportion to exert a strong attrac- ne"^^^^sa°ry,^^to 

 tion for the oxide of nickel, it lets fall a certain quantity prevent the 

 with the arsijnic, till it becomes sufficiently predominant to of^the'Sckdi 

 counterbalance the combined action of the sulphur and ar- 

 senic on the nickel. Whence we perceive, that, to avoid 

 this inconvenience, it is necessary to keep up a slight excess 

 of acid in the liquor, and then we may operate with cer- 

 tainty. 



X. 



On the Experiments of Mr, Chenevix and Mr. DescotIls 

 on Platina : by Mr, C. L. Berthollet*. 



.R. Chenevix published in the Philosophical Transac- Mr Chenevix 

 tions a number of experiments on the combination of pla- combined 

 tina with mercuryf, from which it appeared, that this com- piatina. 

 pound, in certain proportions, was capable of sustaining 

 the strongest fire without the mercury being separated ; 

 that it was fusible ; and that it bore a resemblance to palla- 

 dium. But that celebrated chemist was desirous of his ex- 

 periments being repeated and confirmed, particularly as 

 Messrs Rose and Gehlen announced results contradictory 

 to his. Accordingly I invited him to accompany Mr. Des- 

 cotils to my laboratory at Arcueih 



Mr. Chenevix mentioned the following experiment, which Experirtient 

 he has described in the Annales de Chimie, vol. LXVI, p. pointed out 

 86, as best calculated to elucidate the subject. 



*' Let diluted nitric acid be boiled with a large quantity Nitrate of 

 of metallic mercury, and the result will be a nitrate of mer- mercury at a 

 cury at a minimum of oxidizement^ If this be poured into dg^ ^^ muiiats 



• Annales de Chimie, vol. LXVII, p. 86. 



f See Journal, vol. VII, p. 85, 176 j and XI, p. 162 and 182. 



Vol, XXV. Jan. 1810. F " a m«- 



