68 Dr. Kane on the Compounds oj" Ammonia, 



pound of chloride and amidide of mercury, and the black substance formed by the 

 action of water of ammonia on calomel must be composed of sub-chloride, united 

 to the sub-amiduret of the same metal. More complex examples are furnished 

 by the yellow powder 



Hgcl-\-2 Hgo -{■ Bg . NH2, 

 and the bodies 



UgSO^ + 2 H^O + H^NH^ 

 Hg-NOg+ 2Hg-0 + H^NHj. 



In the copper family there exist some examples equally remarkable, but which 

 shall be referred to particularly under a distinct head. 



Prop. IV. — That amidide of hydrogen can perform the same functions in 

 combination as oxide of hydrogen, whether as basic water, as water of crys- 

 tallization, or as the water termed saline by Graham. 



In the most perfect cases of substitution, where the substances belong to 

 strictly isomorphous groups, the similarity of properties and structure existing 

 through the several classes of bodies formed by the mutually replacing elements, 

 assumes an exactness to which no parallel is found in the instances with which the 

 history of the ammoniacal bodies has supplied us ; yet amongst the combinations 

 described in the preceding sections, analogies and relations have been observed 

 of such closeness, as to give to the truth of the proposition now in question the 

 highest probability. 



A vast number of bodies, such as oxygen-salts, chlorides, iodides, &c., ex- 

 posed to the action of ammoniacal gas, absorb a considerable quantity thereof, 

 and it is afterwards found that different portions of this ammonia are retained 

 with various degrees of force : the greater part being, generally speaking, ex- 

 pellable by the temperature of boiling water, whilst the remainder clings to the 

 substance with a much higher power, sometimes not being separable, unless the 

 constitution of the body be completely broken up. This fact finds a complete 

 parallel in the relative degree of affinity with which water is retained by ordinary 

 salts and acids. Thus the retention of the basic water by oxalic and common 

 tartaric acids, and the greater affinity of the last atom of water in the sulphates of 

 the magnesian class find in the compounds of ammonia their analogous combina-. 



