FUNDAMENTAL CONCEPTIONS 199 



RN = C. It thus became evident that we must distinguish between 

 two cyanogen radicals, viz., one which in its compounds is bound 

 to alkyl, hydrogen, or metal by means of carbon, R C = N, H C = N, 

 MC = N, and another which is joined to these elements or groups by 

 means of nitrogen, RN =C, HN =C, MN =C. We may call the former 

 radical cyanogen, C = N, and the latter isocyanogen, 



-N=C or -N = C; 



these radicals may obviously combine with each other to form three 

 isomers of the empyrical formula C 2 N 2 . The substances discovered 

 by Gautier, the alkylisocyanides, R N=C or R N = C, have 

 properties strikingly different from those of their isomers, the 

 alkylcyanides, R C = N, of Pelouse. They are poisonous, nauseat- 

 ing compounds which affect the throat like prussic acid and color 

 the blood intensely red; they produce violent headaches and vomit- 

 ing. Their odor is most pronounced and persistent. Hofmann, who, 

 in 1868, discovered another method for making them from primary 

 amines, chloroform, and caustic potash, 



RNH 2 +3KOH + CHC1, ->RN=C + 3KC1 + 3H 2 0, 

 found it impossible to work with them except for very short periods. 



An exhaustive study of the reactions of these alkylisocyanides, 

 carried out in 1891-92, led to the definite conclusion that they contain 

 a dyad carbon atom, i.e., they possess the constitution represented 

 by the formula RN: C; the other possible formula with quadrivalent 

 carbon and quinquivalent nitrogen, RN = C, is excluded by the facts. 



The alkylisocyanides belong to the vast category of unsaturated 

 compounds whose chemistry will be briefly discussed from a perfectly 

 general standpoint below; they manifest especially their great chem- 

 ical activity by absorbing other substances forming new molecules 

 in which the valence of carbon has changed from two to four. 

 Such reactions we call additive. Two molecules simply unite to form 

 one new molecule the addition product. A molecule containing an 

 unsaturated carbon atom, i.e., one with two of its valences latent or 

 polarized, RN=C or RN=C], cannot per se show any chemical 

 activity whatever. This is also true of a system containing a pair of 

 doubly or triply bound carbon atoms, ethylene, CH 2 =CH 2 , and acety- 

 lene, CH = CH; and finally of a saturated system which we may 

 represent by a paraffine, C n H 2n + 2, for instance, marsh gas, 



H H 



H H 



All these substances manifest chemical activity simply because they 

 are to a greater or less degree in a dissociated or what may be called 

 an active condition. A given quantity of alkylisocyanide contains 

 an extremely small per cent of molecules with two free affinity units, 



