1819.] Oxides and Salts of Mercury. 247 



diate between the black and red. Dr. Thomson is of this latter 

 opinion. He supposes this deutoxide to be identical with that 

 estimated by Chenevix at 89 - 3 mercury, and 10*7 oxygen, and 

 the same as the yellow powder which appears during the calci- 

 nation of mercury, the mercury first becoming black, next yellow, 

 and lastly red. Other chemists conceive that if heat be applied 

 during the solution of the mercury, the metal unites to several 

 doses of oxygen, according to the degree of heat, the ratio of 

 mercury to the acid, and the length of time ; and that several 

 nitrates may be thus formed, which to alkalies afford precipitates 

 of different colours. The writer of the article "Mercury" in 

 Rees's Cyclopaedia states, that when lime-water is added to 

 solution of nitrate of mercury made in the cold, a yellow preci- 

 pitate appears, which is an oxide distinct from the black and the 

 red. He modifies his calculations accordingly, and describes 

 some of the combinations of this oxide. 



22. With a view of coming to some determination with regard 

 to these veiy different statements, I made cold solutions of 

 mercury in nitrous acid of various degrees of concentration. In 

 some cases, the acid was little stronger than barely to act on the 

 metal ; the latter was added by grains at distinct intervals, and 

 the vessel was kept immersed in cold water. Each of these 

 solutions being decomposed by muriate of soda, the filtered 

 liquor gave with potash a copious deposition of peroxide. I 

 satisfied myself that this was not owing to any partition of oxy- 

 gen during the precipitation, for a nitrate prepared by dissolving 

 black oxide in dilute acid, and precipitated by salt, afforded no 

 peroxide to potash. The numerous trials I made led me to the 

 following general conclusion. 



When nitrous acid of any effective strength is made to act on 

 mercury in the cold, the metal is partly oxidized to the minimum, 

 and partly to the maximum ; the greater the ratio of acid, the 

 greater will be the quantity of peroxide produced. There are, 

 therefore, two nitrates produced together. 



That this solution contains none other but these two salts 

 appears from the following. If the solution, not too acid, be 

 concentrated by evaporation, or without evaporation if the 

 original acid had been about specific gravity 1-280, a quantity 

 of crystals will be formed, which are the real nitrate containing 

 the black oxide, and no other. If the mother liquor be further 

 evaporated, more of the same salt will be obtained ; but when 

 all the nitrate has crystallized, the remaining liquor will be found 

 to contain the peroxide with only the least traces of the black ; 

 and when evaporated to dryness, a white salt will result in every 

 respect resembling that prepared by solution of peroxide in nitric 

 acid. Hence the original solution was a mixture of nitrate and 

 oxynitrate, but not a nitrate of a medium oxide. 



23. The formation of the nitrate in the solution has been sup- 

 posed to be limited by two circumstances ; first, that the solution 



