— 108 — 



improbable that this kind of inodorousness also occurs in nature. In 

 the summer, for instance, the terpene odour of a fir- wood is not so 

 striking in the wood itself as when such a wood is passed on an 

 open road and the wind wafts the odour towards one. 



So far we have only discussed the question of inodorousness in 

 spaces, or of the air in the open. There is, however, also a con- 

 dition of inodorousness of bodies. A body is usually understood to 

 be inodorous, if no molecules at all, or only an infinitesimal number, 

 become detached from the body by evaporation. A glass or platinum 

 vessel is for this reason practically odourless. H. Erdmann 1 ), however, 

 had come to a different conclusion on the strength of his observations 

 respecting the behaviour of odorous substances towards liquid air. 

 Hanny and Horgarths have demonstrated that the capability of 

 dissolving, which liquids possess towards non- volatile bodies, or to- 

 wards such which only volatilise with difficulty, is also found in gases. 

 Starting from this idea, Erdmann examined liquid air as a solvent, 

 and found that three well-known odorous substances, citral, rose oil, 

 and ionone, show a remarkably strong solubility in liquid air, and 

 the author believes that this is a characteristic property of odorous 

 substances. That which is usally called evaporation might therefore 

 also be designated as solution in gaseous air. 



Up to the present it has been accepted that the molecules which 

 volatilise or dissolve in the air, belong to the bodies which chiefly 

 build up the respective substances. In many cases occurring in nature 

 this is not so, for example, in the case of a resin or a wax, in which 

 the odorous particles only represent a small portion. From Erd- 

 mann's point of view the separation of odorous molecules is there 

 simply a transition from one solvent into another. In such case the 

 criterion is not the volatility, but the "coefficient of dissolution". This 

 may be elucidated by the following example: 



A one per cent, solution of (5 -ionone in Paraffinum liquidum is 

 absolutely odourless, although a very large quantity of the odorous 

 substance is present in the liquid. It is therefore necessary to imagine 

 that the coefficient of dissolution between air and paraffin, for /5-ionone, 

 is absolutely in favour of paraffin. If the paraffin solution is shaken 

 with water, the water acquires the most beautiful violet odour. Con- 

 sequently, the coefficient of dissolution is more favourable towards 

 water. Many bodies are therefore odourless, not because they do 

 not possess the volatility of the odorous constituents, . but because the 

 coefficient of dissolution between the latter and the air is exception- 

 ally unfavourable, or, in other words, because the solvent does not 

 permit any appreciable vapour - pressure of the odorous constituent. 



*) Journ. f. prakt. Chem. II. 61 (1900), 225. 



