1819.] Oxides and Salts of Mercury. 243 



boilincr alkaline solution on calomel, the filtered solution on 

 cooling let fall a yellow oxide. These were the circumstances oi 

 the three different results. 



5. From a variety of considerations, to be detailed hereafter, 

 it appeared that the black powder is the real oxide contained in 

 calomel ; and hence as the green oxide is a mixture of the black 

 and yellow, the additional dose of oxygen must be derived from 

 another portion of the black. But as there is no known inter- 

 mediate degree between the black oxide and the metal, I con- 

 cluded that a portion must have been reduced to the metallic 

 state. On submitting some of the powder to the microscope, I 

 observed innumerable minute globules ; and these could be 

 collected into one by triturating the powder, when perfectly dry, 

 in a mortar. By the same management both the grey and black 

 powder (4) afforded metallic mercury. In many cases, the 

 quantity of mercury was alike : the average was about 25 per 

 cent. 



6. The experiments were repeated in various ways on the 

 muriate, nitrate, sulphate, and acetate of mercury, the metal 

 being in the first degree of oxidation in each. With these salts, 

 the solutions of potash, soda, ammonia, and lime, were used : in 

 all cases the mercury was in part reduced to the metallic state ; 

 and in no case could I obtain a pure black oxide. 



7. Hence the whole of the preceding amounts to this, that 

 pure alkaline substances not only deprive the protosalts of 

 mercury of their acid, but also their bases of a part of their 

 oxygen ; and this portion of oxygen, in some cases, unites with 

 the remaining portion of the oxide, and when the quantity is very 

 small passes into new combinations. What these combinations 

 are I have not been able to determine. It is easy to conceive 

 that the minute quantity of oxygen belonging to a few grains of 

 metal might elude detection. It appears, therefore, that the 

 oxide as usually obtained is not the protoxide, but contains either 

 peroxide, or metal, or both ; and hence that the analysis given 

 of this substance must want precision. 



8. To ascertain whether alkalies decompose the oxide con- 

 tained in the oxygenized salts of mercury, I dissolved different 

 portions of pure red oxide in dilute nitric, sulphuric, and muriatic 

 acids. The oxide precipitated from each by a large quantity of 

 potash was found to be unchanged. 



II. Analysis of the Protoxide and Peroxide of Mercury. 



9. From the last section, it appears that pure black oxide of 

 mercury is not obtained by the usual process of decomposition : 

 either the resulting oxide will contain metallic mercury, or part 

 will be brought to the state of peroxide ; while mercury is 

 reduced ; and as this portion, on account of its specific gravity, 

 occupies the lowest stratum, there is hence an unequal distribu- 



Q2 



