496 



SCIENCE. 



[N. S. Vol. XX. No. 511. 



least in saturated compounds. There are 

 also a number of extremely interesting 

 cases where a reaction gives rise to the op- 

 tical antipode. Thus Walden has shown* 

 that 1-chlorsuccinnic acid is converted by 

 silver oxide into 1-malic acid, while potas- 

 sium hydroxide converts it into the dextro- 

 rotatory acid. It is evident that in one 

 case or the other there has been a shifting 

 of the groups. Again Aschamf has shown 

 that when d-camphoric acid is heated with 

 hydrochloric and acetic acids it may be 

 about half converted into 1-isoeamphoric 

 acid, and that the latter suffers a similar 

 transformation. This case is more compli- 

 cated, as a 'cis' and 'trans' isomerism of 

 cyclic compounds is involved as well as the 

 optical difference. Not many cases of this 

 character are known, at present, but such 

 cases certainly deserve further study and 

 must be reckoned with in considering the 

 question we have before us. Le BelJ has 

 already pointed out the theoretical signifi- 

 cance of Waldron's work. 



While we may feel that we have compar- 

 atively sure ground in the application of 

 the theory of van't Hoff and Le Bel to 

 optically active and to cyclic compounds, 

 the case is quite different when we come 

 to the consideration of what are commonly 

 known as 'double' and 'triple' unions. 

 Professor Michael has done a very great 

 service to chemistry in showing that the 

 supposition of a more or less definite tetra- 

 hedral shape for the carbon atom and of 

 'favored' configurations often leads to con- 

 clusions which are at variance with the 

 facts. Philips§ and Blanchard|| and my- 

 self have found a case in which the addi- 

 tion of hydrobromic acid to an unsaturated 

 compound produces an optically active 



*Ber. d. Chem. Ges. 32, 18.55 (1899). 

 t Ibid., 27, 2004. 

 ^ t J. Chim. Phi/s., 2, 344, 1904. 

 § Am. Chem. J., 24, 428. 

 II Ibid., 26, 281; 27, 428. 



body which evidently has the same config- 

 uration as the amino and hydroxy acids 

 from which the unsaturated body is formed 

 by the loss of ammonia or of water. We 

 have here, apparently, a potential asym- 

 metry occasioned by the double union 

 which it is difficult to reconcile with the 

 prevailing conception of such unions. This 

 ease is complicated by the presence of a 

 second asymmetric carbon atom in the 

 molecule and is worthy of further study. 

 Rabe and Billmann* have recently de- 

 scribed a similar ease, but very few in- 

 stances of this kind are known. 



Pfeifferf has recently suggested a new in- 

 terpretation of van't Hoff's hypothesis as 

 applied to unsaturated compounds. Pfeiffer 

 assumes that unsaturated compounds re- 

 tain essentially the same configuration as 

 the saturated compounds, from which they 

 are derived. On this side his interpreta- 

 tion is closely related to the old theory of 

 free valences, which, if I understand him 

 correctly, is favored by Professor Michael. 

 Pfeiffer also brings his interpretation into 

 a close relationship to Werner's theory of 

 inorganic metallic compounds. The most 

 serious objection to the theory is that it 

 supposes the existence either of trivalent 

 carbon atoms or of free valences, in ethy- 

 lene and its derivatives, an objection which 

 has appeared to most chemists very strong 

 in the past. Pfeiffer points out, it is true, 

 that since the discovery of triphenylmethyl 

 we can no longer deny the possible exist- 

 ence of a trivalent carbon atom|. It would 



"Ann. d. Chem. (Liebig), 332, 25. 



t Ztschr. Phys. Chem., 43, 40. 



t The fact that triphenylmethyl exists as a 

 doubled molecule in solution should not, I think, 

 lead us to discard the monomolecular formula 

 for it any more than we consider that acetic acid 

 has, in the ordinary sense of structure, a doubled 

 molecule because it exists as a doubled molecule 

 in solution in benzene or in the state of vapor just 

 above its boiling point, nor because it forms acid 

 salts. In these cases the chemical evidence ap- 



