Chemical Science. 403 



8.4 parts, more of the yellow precipitate were obtained. On ana- 

 lysing this precipitate, the mean of experiments gave sulphuric acid 

 12.6, and peroxide of mercury 87.5 per cent. ; from which it would 

 appear that the salt is a subpersulphate, constituted of 



3 atoms sulphuric acid .... 120 or 12.2 



4 peroxide 864 87.8 



984 100.0 



The acid and oxide remaining in the solution have been supposed 

 to constitute a peculiar supersalt ; but when 4 atoms of bipersulphate 

 of mercury are acted on by water, 3 atoms of acid and 4 of oxide are 

 precipitated, whilst 5 of acid remain in solution ; this dissolving a part 

 of the bipersulphate prevents decomposition of the whole, and the 

 quantity remaining in solution depends, to a certain extent, upon the 

 quantity of water used. 



The carbonates of mercury were then examined. Carbonate of 

 potassa, added to protonitrate of mercury, produces at first a yellow, 

 but, when in excess, a black precipitate. The yellow precipitate dis- 

 solves in acid without effervescence, and was a subprotonitrate ; the 

 black precipitate, when dried by exposure to air, was only black oxide. 



By adding carbonate of potassa to pernitrate of mercury, a preci- 

 pitate with an ochre yellow colour was obtained, which being dried by 

 exposure to air, and then dissolved in nitric acid, lost 4.4 per cent, of 

 carbonic acid; the solution, decomposed by soda, gave 96.1 of per- 

 oxide of mercury. The salt is therefore a dipercarbonate, con- 

 sisting of 



2 atoms peroxide 432 or 95.2 



1 carbonic acid .... 22 4.8 



454 100.0* 



12. ON THE PREPARATION OF THE IODIDES OP MERCURY. 



These compounds may be prepared either by precipating proto or 

 persalts of mercury by iodide of potassium, or by triturating iodine 

 and mercury together. The former has many inconveniences in con- 

 sequence of the effects produced by excess of either precipitate, or 

 by changes effected on the iodide itself by different circumstances 

 influential during its formation. M. Berthemot, therefore, very much 

 prefers the latter, which, a little modified according to his sugges- 

 tion, affords very excellent iodide of mercury. 



The protiodide consists of single proportionals of the elements, 

 consequently, according to Berzelius, of mercury 1265.822 and 

 iodine 789.145, or per cent, of 61.6 and 38.4. These weights are 

 therefore to be taken, put into a mortar with a flat bottom, and tritu- 

 rated together. The mixture soon takes a reddish colour, and upon 

 adding a few drops of the very strongest alcohol, and continuing to 



* Phil, Mag. N; S. ; x. 205. 



