Dr. Kane on the Cotnpounds of Ammonia. 19 



posited are opaque and white, they are generally rhombic prisms. The second 

 (dimorphous) variety described by Mitscherlich I have not analyzed. Their 

 formula is 3Hgo -\-2t<io^-\-Suo, and their composition 



Black oxide of mercury = 82.40 "1 



Nitric, acid = 14.08 1- 100.00 



Water = 3.52 J 



I shall hereafter point out some reasons for considering this to be a double 

 salt. 



It had been long since remarked that these crystallizable salts were decom- 

 posed by water, but great discordance had arisen among chemists as to the 

 nature of the subsalts thus produced. On treating the crystallized nitrates by 

 cold water there remains undissolved a white powder, which as long as the super- 

 natant liquid is acid retains its colour, but if it be washed it becomes yellow. 

 Further, if it be boiled, the brilliancy of the colour is injured, and by long-con- 

 tinued boiling it is converted into a grey powder, which, according to some 

 writers, must be considered as a basic salt. These various phenomena it is 

 necessary to study in detail. 



The white powder, which is formed by the first action of water, I could never 

 obtain in a form justifying any inference from an analysis of it. It is evident 

 that, without freeing it from the liquor holding in solution a quantity of another 

 salt, it would be useless to examine it ; and on the other hand, by washing, the 

 change from white to yellow cannot be avoided ; it was thence necessary to con- 

 sider the yellow subsalt, as being the product to which attention should be paid. 



This yellow sub-protonitrate of mercury can be easily prepared : the white 

 precipitate of which I spoke may be washed with cold water repeatedly, until it 

 is converted into a bright lemori-yellow powder ; by the use of warm water the 

 change may be much accelerated, and the materials may be even boiled for some 

 time without danger, provided that the liquors be not too often changed. The 

 limit is known to have been passed when the brilliant yellow is dimmed by the 

 supervention of a greyish shade. By a very cautious addition of a weak solution 

 of potash, the quantity obtainable from the soluble salt may be very much 

 increased, but the specimens thus prepared are seldom so completely bright and 

 pure as where water alone has been employed in its preparation. 



D 2 



