with Mercurie Iodide. 85 
an equivalent quantity of silver nitrate, also in solution. The 
potassic chloride formed by the first reaction is exactly suffi- 
cient to throw down the whole of the silver as chloride. When 
the silver salt is added, one may remark three precipitates visi- 
ble in the liquid, irregularly blended, scarlet mercuric iodide, 
white silver chloride and the yellow substance resulting from 
their combination. The precipitates are then to be thoroughly 
stirred together to promote combination, which, however, is 
not complete for about twenty-four hours. Meantime the mix- 
oth is salmon colored from the presence of free mercuric 
iodide, 
Obtained in this way, the substance appears as a heavy yel- 
low powder, wholly free from any trace of red, and rather in- 
clining to a greenish or lemon-yellow. This color it always 
exhibits, no matter how prepared, while still wet, even if left 
for weeks. Mixed, however, with gum arabic and spread on 
card-board, it dries to a full chrome yellow. It could not be 
obtained in a condition sufficiently pure for analysis, but there 
can be little doubt that its constitution is AgClHgI. 
e new substance exhibits remarkable properties with re- 
spect to heat. Even below 100° F. it begins to redden, and this 
— rapidly increases with the rising temperature until it 
* : 
gum arabic and be spread on ecard-board, it exhibits the follow- 
ig properties : 
armed gently at a lamp (best by holding it near the glass 
gy 
eated assumes a still deeper color, and returns to the yellow 
much more slowly, setatistenr ‘an intermediate orange shade for 
Some hours. This change is brought about by a sudden and 
inued, the mercuric iodide 
