550 



SCIENCE. 



[N. S. Vol. XII. No. 302. 



meric bodies has been one of the hottest in 

 the recent history of organic chemistry, and 

 not altogether free from invective. Much 

 of this could have been avoided had the 

 organic chemist recognized that the problem 

 is one in which the ordinary methods of or- 

 ganic chemistry find but little application, 

 and then only with the greatest caution and 

 judgment. The older methods are strictly 

 applicable only to the more stable bodies. 

 So impressed has he been with the inertness 

 of the carbon union that he has failed to 

 recognize that the laws of chemical equi- 

 librium could have any place in organic 

 chemistry. A certain compound may, for 

 example, contain one of the two groups : 



=CH =C 



I or II 



— C=0 — COH 



The organic chemist assumed that it must 

 be entirely the one or entirely the other, 

 and was perplexed on finding that it reacted 

 with a ketone reagent entirely in the former 

 sense, and with a hydroxyl reagent enbirely 

 in the latter. To get around the difiiculty, 

 he was led to assume with Baeyer that only 

 one of these actually exists in the free state, 

 or with Laar, that each molecule is rapidly 

 changing from the one form to the other 

 and back again. The most elementary 

 knowledge of reversible reactions would 

 have taught him that the two forms must 

 necessarily tend to a condition of equilib- 

 rium ; that the final product must be a mix- 

 ture of both forms, but that equilibrium 

 might lie at a considerable distance from 

 both extremes, or very near to one ; that 

 either form, if isolated, would tend with 

 greater or less rapidity to the same condi- 

 tion ; that if he removed one constituent by 

 converting it into another compound, the 

 equilibrium would be disturbed, and more 

 of the other form would undergo transfor- 

 mation and be removed from the sphere of 

 action until conversion is complete, and 

 that, therefore, conclusions based on purely 



chemical evidence were to be accepted with 

 a grain of salt unless the two forms, by 

 virtue of their slow velocity of transforma- 

 tion, could be isolated and studied. The 

 application of physico-chemical methods 

 nowhere in organic chemistry finds better 

 opportunity than in just this field. In 

 some cases the laws of the so-called ' con- 

 densed systems,' with definite inversion 

 temperatures, are doubtless applicable. 

 Hantzsch's researches on the nitro-hy- 

 drocarbons afford a good illustration of 

 the superiority of physico-chemical meth- 

 ods. Mtroethane C2HJ.NO2 is a good ex- 

 ample of this class. Its constitution was 

 assumed by its discoverer, Victor Meyer, to 

 be CHj.CHj.NOj, and it forms salts with al- 

 kali metals, in which the metal has been 

 variously supposed to be united to carbon 

 CH3.CHM.NO, or to oxygen CHj.CH^ 

 l^rO.OM ; in the latter ease it was neces- 

 sary to assume either that the originally 

 proposed formula of nitroethane is wrong, 

 or that in forming a salt it undergoes intra- 

 molecular rearrangement. Hantzsch now 

 applied the method of electrical conduc- 

 tivity. The aqueous solution of nitro- 

 ethane is practically a non-conductor, and 

 hence contains no ions, which would make 

 it decidedly not an acid. If this solution 

 be mixed with the equivalent of caustic 

 soda, it at first shows only the conduc- 

 tivity due to the alkali ; gradually, how- 

 ever, this diminishes, indicating the slow 

 formation of a salt, which, being the salt 

 of a weak acid and therefore less dissoci- 

 ated than caustic soda, would conduct less. 

 "Were the nitroethane itself an acid, this 

 effect should take place at once, as salts 

 always form instantly or nearly so. If now 

 just sufficient hydrochloric acid be added 

 to convert the sodium nitroethane into 

 nitroethane and sodium chloride, the solu- 

 tion at first shows a greater conductivity 

 than is attributable to the sodium chloride 

 alone; the nitroethane, therefore, takes 



