on the Haloid Compounds of Mercury. 441 
Rose and Grouvelle have already shown that when dry ammonia is passed over 
melted sublimate, an atom of the former is absorbed by one of the latter, and a white 
mass formed. The history of its properties has been so well given in Rose’s Memoir, 
that it is unnecessary for me to do more than mention my results as having been con- 
firmatory of his. This compound is decomposed by water giving white precipitate and 
sal-alembroth, as may be at once seen : 
4 (2 Cl+Hg)+4 NH = 
§ (2Cl+ Hz) + (@NH?+ Hg) +2 fe Cl +Hg) +(Cl + NH)? 
Section II.— Of the Action of Ammonia on the Proto- Chloride of Mercury. 
§1.—Aection of Liquid Ammonia upon Calomel. 
The decomposition resulting from the action of water of ammonia upon the proto- 
chloride of mercury, does not appear to have attracted particular attention, as all 
writers who speak at all upon the subject, mention ammonia, along with potash and 
soda, as decomposing calomel into black oxide of mercury. Hennell in particular, 
states expressly, that calomel decomposed by excess of ammonia, yields a black powder 
containing in 100 parts, 96 of mercury and four of oxygen. I was therefore rather 
surprised when experiment showed me that a reaction of a totally different nature 
takes place, giving rise to a compound possessed of very remarkable properties. 
When water of ammonia is poured on calomel, whether sublimed or precipited, the 
the mass immediately becomes black, and the appearance is not altered by boiling the 
mixture for a long time. While yet wet the powder remains almost black, but it 
becomes much lighter on drying, so that when quite dry it is of a dark-grey. This 
powder is not altered by exposure to air, or to a moderate heat ; a portion of it was 
exposed in a platinum crucible on a sand bath for several hours to a temperature of 
180° Fahrenheit, without being altered in weight or colour. When moistened it 
becomes nearly as dark as when first generated, but it again loses its black colour on 
being dried: boiled with water it does not appear altered in its composition. When 
this powder is heated in a tube sealed at one end, it first gives a trace of water, with 
much azote and ammonia; then there sublimes calomel mixed with metallic mer- 
