204 CHEMISTRY 



H 



Cl 



For this reason the majority of the addition products of the isoni- 

 triles can be kept only for a short time; this property rendered 

 futile many attempts to isolate definite addition products. The 

 continual dissociation of such products sets free active or disso- 

 ciated alkylisocyanide particles, and these slowly condense with one 



another, xRN=C^ (RN=C)x, giving rise to the so-called al- 



kylisocyanide resins (non-reversible), products whose molecular 

 weight has not yet been determined and which are perfectly analogous 

 to azulmic or polymerized prussic acid. Consequently in carrying 

 out an addition reaction with an isonitrile, especially if it requires 

 much time or a temperature above 20, large quantities of these resin- 

 ous polymers are formed from which it is possible to isolate the addi- 

 tion product only with great difficulty. 



Many of the isonitriles themselves even when perfectly pure undergo 

 rapid polymerization to resins so that they can be kept only for a very 

 short time. Phenylisocyanide, C 6 H 5 N=C], is the most striking in- 

 stance, as it changes in a few minutes from a colorless to a dark blue 

 liquid, and in a few days condenses to a dark brown resin. Have we not 

 here a possible explanation of the fact that it is impossible to isolate 

 methylene and a large number of its derivatives, although marsh gas, 



H H H 



methyl alcohol, and chloride of methyl, H 2 C H 2 C H 2 C 



H OH Cl, 



all contain a relatively small per cent of active methylene particles 

 at ordinary temperatures? 



The presence of bivalent carbon in the alkylisocyanides having 

 been established, the next question presenting itself was whether 

 prussic acid and its salts contain the cyanogen or the isocyanogen 

 radical. In the latter case, H N = C, M N = C, these substances 

 must be analogous to Gautier's isonitriles. It had hitherto been con- 

 sidered as established, but without sufficient evidence, that prussic 

 acid and the cyanides were cyanogen compounds analogous to the 

 nitriles of Pelouse. 



When one considers the physical and physiological properties of 

 prussic acid [boiling-point 25, specific gravity 0.7, a violent poison] 

 and contrasts these with the corresponding properties of methyl- 

 cyanide [boiling-point 81, specific gravity 0.81, sweet-smelling harm- 

 less oil] and of methylisocyanide [boiling-point 58, specific gravity 

 0.75, a poison], one at once comes to the conclusion that prussic acid 



