1819.] Oxides and Salts of Mercury. 251 



38. The analysis of this oxide is stated by Paysse at 18 per 

 cent of oxygen. Chaptal obtained so much as 20 per cent, 

 while what is considered peroxide contains but 7 or 8. From 

 this, red precipitate would appear to be a distinct oxide, and 

 that in the highest degree of oxidation. 



To ascertain this point, I heated 50 gr. of red precipitate for 

 10 minutes in a green glass tube to about 350°, and obtained 

 ^ of water, which I afterwards found to be hygrometric. The 

 analysis was then conducted in the manner already detailed (13); 

 the reduced mercury being scraped down, the tube filled with 

 hydrogen, and the heating repeated, for all this was necessary, 

 although it was not in the case of calcined mercury. In this 

 manner I was surprised to find that the analysis of this exactly 

 corresponded with that of calcined mercury, the oxygen amount- 

 ing to but 7-2 per cent, instead of 18 or 20. Perhaps Paysse 

 and Chaptal examined a red precipitate which contained some 

 undecomposed nitrate of mercury. 



Hence it appears that red precipitate is precisely the same as 

 the red oxide prepared by calcination ; and it is no objection to 

 urge the poisonous and escharotic effects attributed to the 

 former ; they apply equally to both, or more properly to neither. 

 John de Vigo used red precipitate internally in the dose of three 

 or four grains as a remedy against the plague. Mathiolus, 

 almost three centuries ago, used it in the cure of the venereal 

 disease in the dose of five grains, but declares it dangerous 

 unless previously well washed in plantain water. Lemery him- 

 self gave it in doses of three or four grains. For my own part I 

 ventured, as an experiment, to take it in the dose of one grain 

 at intervals of two days, but well levigated, and I could find no 

 effect of any kind from it. When it produces violent effects, it 

 perhaps has not been well levigated, or contains undecomposed 

 oxynitrate. 



From all the foregoing observations on the combinations of 

 nitric acid and mercury, it appears that none of these salts 

 afford any other oxide than the black and the red. We shall 

 next proceed to the consideration of the sulphuric acid. 



(To be continued.) 



Article II. 



On Cyder Making, with Queries. By the Rev. J. Venables. 



(To Dr. Thomson.) 



SIR, 



As I have always considered the scientific journals of the 

 present day as a medium through which not only the learned 

 may communicate the result of their researches to the public, 



