— ii 4 — 



smell. The double or triple linking need not always exist between 

 two carbon atoms; groups such as C : O and C : N or C ! N are 

 in the same manner important as compared with the less strongly 

 smelling compounds with the groups C • O and C • N. As a proof, 

 Miss Woker mentions on the one hand the aldehydes, ketones 

 and acids, and also the nitriles, and on the other the alcohols and 

 amines. In connection with the C — N derivatives the authoress dis- 

 cusses the difference in the odour between nitriles and the isomeric 

 carbylamines, which, compared with the former, are still less satur- 

 ated. The more powerful influence of two double linkings in com- 

 parison with a triple linking, is exemplified by the odoriferous properties 

 of the iso (-thio-) cyanic esters and the normal esters. Important is 

 the entrance of sulphur in the place of oxygen in the thio alcohols and 

 esters, and in the place of the group — C H : C H — in the thiophene 

 derivatives. An accumulation of the same atoms or atom complexes 

 (in the case of the terpene derivatives, chiefly of CH 3 - groups) increases 

 not only the intensity of the odour, but also the volatility of the com- 

 pounds, for example, it is well known that of the isomeric butyl alcohols, 

 the one with the largest number of methyl groups, i. e. the tertiary 

 butyl alcohol, has the lowest boiling point. Ring-closure of an aliphatic 

 into a hydroaromatic body is said to exert no special influence on the 

 odour. The example citral — pulegone taken from the terpene series 

 is, however, not a very happy one, and it would perhaps have been 

 better if the authoress had substituted for it the comparison, originating 

 from Per kin jun., of his aliphatic terpineol 



CH— CH 2 (CH 8 ) 2 



CH 3 — CH 2 OH 



with cyclic a -terpineol 



CH — CH 2 (CH 3 ) 2 



CH 2 — CH 2 OH 



If, on the other hand, double linkings disappear during the ring- 

 formation, as, for example, in the formation of trithio aldehydes, 

 cyanuric acid derivatives, and similar polymerisations, the smell also 

 disappears. Under certain conditions, several factors influencing the 

 smell are able to neutralise each other, as is proved for instance by 

 uric acid, in which three CO -groups, the ethylene groups, and four 

 multiple-linked N- atoms, yield a completely odourless body. 



The comparisons made by the authoress are drawn from bodies 

 which she has not studied herself, but taken from Krafft's Text- 

 book of Organic Chemistry. It is, however, a well-known fact that the 



