1820.] Physical Science during the Year 1819. 41 



is deprived of a portion of its acid by water, and converted into 

 subpersulphate. 



Mr. Donovan has not subjected any of the persulphates of 

 mercury to analysis ; had he done so, I believe he would have 

 ■changed his nomenclature a little. The white persulphate is in 

 reality a bipersulphate, while the yellow powder obtained by 

 washing the former salt in hot water is a neutral persulphate. 



1 1 . Nitrate of Silver. — The method of obtaining a pure nitrate 

 of silver from standard silver, which is an alloy of that metal 

 with copper, given in the Annals ofPhilnaophy, xv. 389, deserves 

 the attention of practical chemists. It consists in this : The 

 alloy is dissolved in nitric acid, and the solution evaporated to 

 dryness in a glass vessel. It is then put into an iron spoon, and 

 exposed to a moderate heat, keeping the salt in fusion till all 

 ebullition is at an end. By this heat the nitrate of copper is 

 decomposed, while the nitrate of silver remains unaltered. 

 Dissolve the salt in water, filter and evaporate the colourless 

 solution, and we obtain nitrate of silver in a state of purity. 



12. Muriate of Gold-and-Soda. — This is a triple salt, which 

 has been prepared by M. Figuier, of Montpelher. It is employed 

 in medicine tor the purposes recommended by M. Chretien. The 

 method of preparing it is abundantly simple. Gold is dissolved 

 in aqua regia, and the solution made as neutral as possible by 

 evaporating to the consistence of a syrup. It is then diluted 

 with water, and mixed with a solution of common salt. By the 

 requisite concentration, permanent crystals of the triple salt are 

 obtained. The figure of the crystals is a thin rectangular paral- 

 lelopiped, which does not attract moisture from the atmosphere. 

 The constituents of this salt, according to the analysis of Berard 

 and Figuier (with the details of which, however, they do not 

 furnish us) are as follows : 



Muriatic acid 19*75 



Oxide of gold 60-76 



Soda c 8-50 



Water 20-99 



100-00 



(Journ. de Pharm. vi. 64.) 

 13. Ferrochyazate of Iron.-. — My experiments on this salt have 

 80 recently made their appearance in the Annals of Philosophy ^ 

 XV. 392, that it seems to be necessary merely to allude to them. 

 It is a neutral salt, when pure, composed of one atom of ferrochyazic 

 acid + one atom peroxide of iron. I am inchned to ascribe the 

 pyrophorous quality which the residue of this salt, after exposure 

 to a red heat in close vessels, is known to possess, to the presence 

 of a little potash^, from which it is exceedingly difficult to free 

 the salt. This potash is probably converted into potassium 

 during the process of heating, and the rapidity with which it 



