400 PRINCIPLES OF CHEMISTRY 



urea. This remarkable isomeric transformation was discovered by 

 Wohler in 1828. It had an important historical signification, because 

 at that time such an easy formation outside the organism of those 

 substances which are met with in it was quite unexpected, it being at 

 that time supposed that the vital force of the organism produced sub- 

 stances which could not be formed outside it. But in addition to the 

 abolition of this presupposition, the easy transition of NH 4 OCN into 

 CO(NH 2 ) 2 is the best example of the transition of one state of 

 atomic equilibrium into another more stable one. Every carboxyl 

 acid, RCOOH, has its corresponding amide, RCONH 2 , 41 and 

 nitrile, as is the case with carbonic acid. In this way, formamide, 

 HCONH 2 , and hydrocyanic acid, HCN, as a nitrile, correspond 

 -with formic acid, HCOOH, and therefore ammonium formate, 

 HCOONH 4 , and formamide, under the action of heat and substances 

 which take up water (phosphoric anhydride), form hydrocyanic acid, 

 HCN, whilst, under many conditions (for instance, on combining with 

 hydrochloric acid in presence of water), this hydrocyanic acid forms 

 formic acid and ammonia. Although containing hydrogen in the 

 presence of two acid-forming elements namely, carbon and nitrogen 42 

 hydrocyanic acid does not give an acid reaction with litmus (cyanic 

 acid has very marked acid properties), but forms salts, MCN, and 

 therefore presents the properties of a feeble acid, and for this reason is 

 called an acid. The small amount of energy which it has is shown 

 by the fact that the cyanides of the alkali metals for instance, potas- 

 sium cyanide (KHO -f HCN = H 2 O + KCN) in solution have a strongly 



41 The majority of the amides corresponding with acids, being represented by the com- 

 position RNH 2 , very easily undergo the inverse change ; they combine with water, even 

 when simply boiled with it, and still more so under the action of alkalis and acids. Ammonia 

 is evolved by the action of alkalis on amides, naturally in virtue of the water combining 

 with the amide, in addition to which there is formed a salt of the acid, which had served to 

 form the amide according to the equation : RNH 2 + KHO = RKO + NH 3 . The same thing 

 takes place under the action of acids, only, naturally, an ammonium salt of the given 

 acid is formed, and the acid, previously in the condition of an amide, st-jmrutes in the 

 free state: RNH 2 + HC1 + H 2 O = RHO + NH 4 C1. Thus the amides, in the majority of 

 cases, easily pass back into ammonium salts in the presence of water, alkalis, and acids ; 

 but they differ in a marked way from them. None of the ammonium salts are distillable, 

 nor volatilise without change ; in most cases ammonia salts, on being heated, lose water 

 and form amides ; many amides volatilise without change, and sometimes are crystalline 

 volatile substances easily distilled. Such are, for instance, the amides of acetic, benzoic, 

 formic, and a large number of other organic acids. Judging from the preceding facts, 

 amides may be regarded as acids RHO, in which the hydroxyl HO is ivpliir.-d by the 

 ammonia radicle (amidogen) NH 2 . 



42 If ammonia and methane (marsh gas) do not show any acid properties, that is in all 

 probability due to the presence of a large amount of hydrogen in bo'th ; but in hydro- 

 cyanic acid one atom of hydrogen is under the influence of two acid-forming elements. 

 Acetylene, C 2 H 2 , which contains but little hydrogen, presents acid properties in certain 

 respects, because its hydrogen is easily replaced by metals. 



