On some of iht Combinations cf Mercury. 51 



The pronitrates aro converted by a gentle lieat into a red com- 

 pound, in a state of minute mechanical subdivision. Khombic 

 and yellow pronilrates, by exposure to a gentle heat, also give 

 the same compound, the proportion obtained from yellow 

 pronitrate being smallest, and increasing according to the 

 quantity of acid contained in each pronitrate, that from the 

 hexagonal pronitrate being nearly equal to the quantity of 

 mercury which it contains. The reason of this obviously is, 

 that the oxygen required for the peroxidation of the mercury is 

 derived from the acid, which in the yellow and rhombic proni- 

 trates being comparatively small, there is but a small quantity 

 of metal paroxidized, the remainder being evaporated and lost. 

 Red precipitate, or nitroxide of mercury, has been usually 

 considered as apeioxide of mercury containing a small quantity 

 of nitric acid and a larger quantity of oxygen than is contained 

 in any other oxide of mercury. I urn led to conclude, however, 

 that this view is erroneous, and that, when properly prepared, 

 it conlains no nitric acid, and no more oxygen than is contained 

 in the red oxide procured from the pronilrates, or in that pro- 

 cured by exposing mercury to the action of oxygen with the 

 assistance of heat ; that in fact, these processes all give the same 

 compound, for each, when triturated with metallic mercury and 

 nitric acid in the manner formerly described, oxydates the same 

 quantity of mercury and affords the same compound. I there- 

 fore am inclined to believe, that, in making the experiments 

 from which the common opinion is drawn, a preparation had 

 been used in which the process of its preparation had not been 

 continued sufficiently long, and that a portion of the pernitrate 

 of mercury had remained undecomposed, thus influencing the 

 products of the analysis. It appears to me, therefore, that the 

 pronitrates may be used with advantage in preparing the red 

 oxide of mercury instead of pernitrate ; or instead of exposing 

 mercury to heat in the open air ; because of the comparatively 

 little tiouble with which it may be procured, and because, com- 

 part d with the oxide procured from the pernitiate, of the greater 

 facility with which it may be obtained pure, and in a state of 

 minute subdivision. 



Having shown that pronitrate of mercury may without dif- 

 ficulty be obtained free from intermixture with pernitrate, it 

 appears to me that pure protochloride of mercury (calomel) may 

 be made advantageously by precipitation. The process usually 

 recommended lor this purpose does not succeed, not merely 

 because a pure proniirate is frequently not obtained, but be- 

 cause the compounds resulting irom the action of chloride of 

 sodium (common salt) and pronitrate of mercury, are not 

 nitrate of soda and protochlorids of mercury, alone, but to- 



