198 CHEMISTRY 



To be sure there were many chemists who preferred to consider the 

 valence of carbon in carbon monoxide as four, thus making the valence 

 of oxygen four, C = ; and when we bear in mind that the other mem- 

 bers of the oxygen group, sulphur selenium and tellurium, exist as 

 di-, tetra-, and hexavalent atoms, there is some justification for this 

 interpretation. To me personally, however, it seems in the highest 

 degree improbable that two atoms should be thus bound to each other 

 by four affinity units. 



About fourteen years ago a series of systematic experiments was 

 undertaken with the object of ascertaining whether carbon can exist 

 in a bivalent condition. The experiments have established this pornt 

 in a most decisive manner; we have now quite an array of substances 

 which contain bivalent carbon. Furthermore it has been possible 

 to prove, from the experience gained in their study, that methylene 

 chemistry plays an important role in many of the simplest reactions 

 of organic chemistry, reactions which have hitherto been explained 

 on the basis of substitution. At the time when these experiments 

 were undertaken there existed besides carbon monoxide several sub- 

 stances which might contain bivalent carbon namely, prussic acid 

 and its salts the cyanides, HN=C and MN=C. Also the so-called 

 carbylamines, RN=C, discovered in 1866 by Gautier. 



These substances were, therefore, exhaustively studied in order to 

 establish rigidly by experiment whether bivalent carbon was present 

 or absent. The presence of dyad carbon having been established and 

 its properties thus being known, the problem then presenting itself 

 was the isolation of methylene and its homologues. 



You are probably all aware that Gay Lussac established in 1815 

 the existence of a radical, composed of one atom of carbon and one 

 of nitrogen, in prussic acid and the cyanides. This radical, cyanogen, 

 plays in its compounds a role similar to that of the elements of the 

 halogen group. 



In 1832 Pelouse discovered the alkylcj^anides, R C = N, by treating 

 cyanide of potash with alkyliodides or with alkylpotassic sulphates, 

 KCN + RI or ROSO 2 OK^R-C = N + KI or KOS0 2 OK, an appar- 

 ent double decomposition reaction by which we obtain a compound 

 in which the radical R(=Cn H 2n+1 ) is joined to the cyanogen group 

 by means of carbon. The alkylcyanides thus obtained are neutral, 

 pleasant-smelling, harmless liquids, resembling ether, chloroform, 

 and the alkylhalides, RC1, RBr, and RI. 



In 1866 Gautier discovered by treating cyanide of silver with alkyl- 

 iodides, RI + AgNC^RN=C + AgI, also an apparent double decom- 

 position reaction, a new class of organic compounds; they are iso- 

 meric, not identical, with the alkylcyanides of Pelouse. He called 

 them the carbylamines or isonitriles, and proved that the alkyl group 

 is bound to the cyanogen radical by means of nitrogen RN=C or 



