292 Facts towards the 



silver or mercury from the list of chemical compounds, because 

 slight mechanical me-ans suffice to decompose them. 



Calomel boiled in excess of solution of soda, or treated with ex- 

 cess of ammonia, yields a black powder, which, if carefully dried 

 out of the contact of air, affords, on decomposition, about ninety-six 

 per cent, of mercury, and four of oxygen ; or 200 of mercury and 

 eight of oxygen ; while the red oxide of mercury, a crystalline, 

 permanent and definite compound beyond all doubt, affords 200 

 of mercury and sixteen of oxygen. There is, therefore, every 

 reason for adopting the former as a true combination, for we 

 find that it is entirely soluble in and forms distinct salts with acids, 

 and that it contains just half the proportion of oxygen existing in 

 the peroxide. It is nevertheless true, that by a gentle heat, by tri- 

 turation, or by exposure to light, this protoxide throws off a portion 

 of its mercury, whilst the remainder of the metal passes into the 

 state of peroxide. 



§ II. Of the Sulphurets of Mercury. 



In respect to the sulphurets of mercury, M. Guibourt is of opi- 

 nion that the protosulphuret is to be considered as a mixture 

 (un melange) of cinnabar and metallic mercury, because it is as 

 easily decomposed as the protoxide ; nevertheless he shows that it 

 consists of 200 of mercury and sixteen of sulphur, and that the bi- 

 sulphuret, or cinnabar, is composed of 200 mercury and thirty-two 

 sulphur : there seems, therefore, no reason whatever for assuming 

 the protosulphuret to be an indefinite mixture ; and if it be con- 

 sidered, as some would have it, a compound of cinnabar and mer- 

 cury, what is that but a protosulphuret, as proved by its analysis ? 

 Respecting the mode of obtaining the protosulphuret, there may, 

 however, be some difference of opinion. It appears to us that the only 

 method bywhichsuch a definite compound can be procured, consists 

 in passing sulphuretted hydrogen gas into a very dilute solution of 

 the protouitrate of mercury, or into water through which calomel 

 is diffused ; in either case, a perfectly black precipitate is formed, 

 which, when collected upon a filter, and very carefully dried, exhibits 

 no globules of mercury, and which, when analyzed, affords results 



