124 Report of Schimmel 8j Co. April/ October 1917. 



Henning refers to the fact that scent-producing groups, ("osmophores"), owing to 

 the possibility of their being mutually exchanged without a fundamental alteration of 

 their odour, (for instance nitrobenzene and benzaldehyde), cannot be 

 the sole determinants in producing the smell of any compound, but rather /\ 



that the whole manner in which these groups are combined in the model: f 

 molecule is the deciding factor in producing odours. There is no doubt 

 whatever that the osmophoric group must combine with some „osmo- 

 gene" radicle or other in order to produce a smell of any kind. In this case, the 

 smell depends on the manner the osmophores are combined with the osmogene nucleus. 



Henning draws the conclusion from this consideration that the formulae of the 

 chemical representatives of his 6 odour-classes (vide his odour-prism) 1 ) must — within 

 each psychological division — have something in common as to the manner they are 

 linked up to each other, and in point' of fact without depending upon the circumstance 

 to which chemical family these perfumes may belong to. 



This hypothesis was confirmed on investigating all aromatic compounds whose 

 constitutional formula was known. The hexagon benzene nucleus is employed as a 

 fundamental model of the various odours. Under these circumstances, the formulae of 

 the perfumes belonging to one and the same psychological odour-class, for instance to 

 the aromatic class, are linked up in the same manner. The characteristic of the aromatic 

 scents would then be that there osmophoric groups are in a para position to each other. 



The odour-prism proves that, for instance, anise aldehyde, anethole, chavicole, 

 methyl chavicole, ^-cresol methylether which all are para derivatives belong to the 

 class of the spicy scents. The model is, however, also applicable to bodies of the 

 aliphatic series if one regards them as an open hexagon with lateral chains. This 

 structure applies to many fruit-scents, for instance, to linalool, citral, and to methyl- 

 heptenone. We must restrict ourselves here only to giving some indications of the 

 scope of this theory, as the author has reserved the right to expound it more fully 

 in a chemical review; however, it is doubtful if it can lay a claim to general application 

 in its present form, because — in order to give only one instance — cinnamaldehyde 

 does not show the para position, demanded by Henning, although odoro-psychological 

 test places it beyond doubt in the class of the spicy scents. 



In reference to the physical nature of odours, the conception was current already 

 in ancient times that perfumes emanate material particles which are perceived by the 

 nasal organs, and this is the so-called "corpuscular theory". The "wave theory" of 

 odours which was in vogue at one time can be regarded as decidedly antiquated. Our 

 present knowledge of the physical and chemical qualities of smelling compounds gives 

 the palm to the former theory. This supposition is also supported by physiological 

 and psychological facts. 



Another question which has been much discussed is the problem in what manner 

 one can most accurately measure any odour. In spite of many experiments, no method 

 has hitherto been evolved for doing this in a faultless manner. After discussing the 

 various methods in use hitherto for this purpose, Henning describes an apparatus, 

 consisting of a modification of the oldest method conceived by Valentin, and which 

 is based on the determination of weight. 



However, the measurement according to the volumetric method has proved to be 

 more convenient, and for this object he describes an apparatus which has been adapted 

 from vessels employed for gas-measuring purposes. 



i) Bericht 1916, 114. 



