IRON, COBALT, AND. NICKEI* 847' 



double decomposition, being in the state of- the complex radicles CJ$ y 

 NH 4 , NO 2 . Such a representation is, however, completely superfluous 

 for the explanation of the peculiarities in the reactions of such com- 

 pounds as double salts. If a magnesium salt which can be precipitated 

 by potassium hydroxide does not form a precipitate in the presence of 

 ammonium dbloride, it is very clear that it is owing to the formation 

 of a soluble double salt which is not decomposed by alkalis. And 

 there is no necessity to account for the peculiarity of reaction of a 

 double salt by the formation of a new complex radicle. In the same 

 way also, in the presence of an excess of tartaric acid, cupric salts do 

 not form a precipitate with potassium hydroxide, because a double salt 

 is formed. These peculiarities are more easily understood in the case 

 of cyanogen compounds than in all others, because all cyanogen com- 

 pounds,, as unsaturated compounds, show a marked tendency to. 

 complexity. This tendency is satisfied in double salts. The appear- 

 ance of a peculiar character in double cyanides is the more easily 

 understood since in the case of potassium cyanide itself, and also in 

 hydrocyanic acid, a great many peculiarities have been observed 

 which are not encountered in those haloid compounds, potassium 

 chloride and hydrochloric acid, with which it was usual to compare 

 cyanogen compounds. These peculiarities become more comprehensible 

 on comparing cyanogen compounds with ammonium compounds. Thus 

 in the presence of ammonia the reactions of many compounds change 

 considerably. If in addition to this it is remembered that the 

 presence of many carbon (organic) compounds frequently completely 

 disturbs the reaction of salts, the peculiarities of certain double cyanides 

 will appear still less strange, because they contain carbon. The fact 

 that the presence of carbon or another element in the compound pro- 

 duces a change in the reactions, may be compared to the action of 

 oxygen, which, when entering into a combination, also very materially 

 changes the nature of reactions. Chlorine is not detected by silver 

 nitrate when it is in, the form of potassium chlorate, KC10 3 , as it is 

 detected in potassium chloride, KC1. The iron in ferrous and ferric 

 compounds varies in its. reactions. In addition>to the above-mentioned 

 facts, consideration ought to be given to the circumstance that the 

 easy mutability of nitric acid undergoes modification in its alkali 

 salts, and in general the properties of a salt often differ much from 

 those of the acid. Every double salt ought to be regarded as a pecu* 

 liar kind of saline compound : potassium cyanide is, as it were, a basic* 

 and ferrous cyanide an acid, element. They may be unstable in the 

 separate state, but form a stable double compound when combined 

 together ; the act of combination disengages the energy of the elements, 



