Notes on scientific research. 117 



In this manner one obtains lines running almost parallel to each other. The same 

 applies to the table II and IV; in this case the lines run in a different manner, but in 

 the same sense. 



Table IV. Critical distances for fatty acids expressed in centimeters. 



Substance. l Jion. 1 J2on. Y 400 - Vsoii- l jun.n. l jmn. 7«ioff. 



Formic acid ...... 1.2 — — — — — 



Acetic acid 20 0.5 — — — 2 



Propionic acid 81 50 — — — — 20 



Butyric acid 125 85 — — — — 74 



(Iso) Valeric acid .... 170 173 — — — 78 



Caproic acid .....— 190 180 177 160 132 106 



Caprylic acid — — - — — — 90 



Experiments with mixtures have proved that the charging phenomena in this case 

 are additive; accordingly mixtures which have an exceedingly faint or scarcely per- 

 ceptible odour in which, therefore, a considerable scent-compensation has taken place, 

 can — owing to this additive quality — show an increased charging capacity. 



The results are quite different in cases in which the components of a mixture react 

 chemically on each other, for instance with compounds such as aniline and acetic acid 

 which produce acetanilide. If under this circumstances a compound is to produce an 

 electrical charging phenomenon, it must conform to the following conditions: — 



1. It must be soluble in water (compounds which are totally insoluble in water do 

 not show this phenomenon at all); 



2. It must reduce the surface tension of water. 



3. It must, when finely divided over a great surface, become volatile from the solution. 

 Acetanilide conforms to the conditions 1 and 3 and really belongs to the strange group of 



organic compounds which produce the charging phenomena, just like perfumes themselves. 

 If the compounds which conform to the above-mentioned 3 conditions are also per- 

 fumes by nature, they must be able to adapt themselves to two further ones, namely: — 



4. of being soluble in lipoids (all perfumes are soluble in fatty oils) 



5. of containing an odorophorous group in their composition. 



Acetanilide hardly conforms to the condition N° 4, but the aniline and acid radicles 

 can be regarded as forming an odorophorous group. Rupe and von Majewski 1 ) suspect 

 that, in case a molecule contains 2 odorophorous groups possibly they tend to neutralize 

 each other in their effects. This fact, besides its insufficient solubility in oil, might 

 explain the odourlessness which is a characteristic of acetanilide. 



Besides the above-mentioned publications, papers by E. L. Backman 2 ) on the olfacto- 

 logie of the methylbenzene series and by C. Huijer 8 ) on the olfactologie of aniline and 

 its homologues. Backman has found inter alia that the minimum perceptioile of the 

 perfumes in the methylbenzene series, in so far as it applies to the first 4 links, (benzene, 

 toluene, xylene and pseudocumene), regularly diminishes with the increase in the number 

 of the methyl-groups. However, the intensity of scent increases under these circum- 

 stances first of all. The odour turns from an empyreumatic one (benzene — toluene) 

 to an aromatic one (xylene — pseudocumene) and then into a phenolic one (durene). 



l ) K. von Majewski, Beitrage zur Kenntais der Diazoimidobenzolderivate. Inaug.-Dissert., Basel 1898. — 

 2 ) Koninkl. Akad. van Wetensch., Amsterdam 25 (1917), 971; meeting of Jan. 27 th . According to a kindly 

 forwarded referate impression. — 3 ) De olfactologie van aniline en homologen. Inaug.-Dissert., Utrecht 1917. 

 According to a copy kindly forwarded. 



