132 



diffused liglit lias been measured af(er the melliod of Kamerlingh 

 Onnes and Kkesom-). The values of the quantitative determinations 

 in the series of the aqueous solutions are in the ratio of 43:39: 

 : 37 : 20 : 15 : 15 : 10; in the paraffinous solutions 23:18: slight. 



Besides the above solutions also the aqueous solutions of apiol, 

 creosol, paraxylenol, anysaldehjd appeared to yield a markedly 

 distinct effect. The Tyndal phenomenon is fairly distinct in old 

 aqueous solutions of xylidin, orthotoluidin, chinolin, durol. A moderate 

 effect we discovered of old aqueous solutions of methylcinnamylate, 

 paratoluidin, salicylaldehyd, naphtalin, cnmarin, toluol, anthranil- 

 acid methylester, benzylbenzoate. A very slight effect was evinced 

 by aqueous solutions of safrol, vanillin, anthracene, nitrobenzol. 

 Tyndall's effect did not appear in old aqueous solutions of iron, 

 heliotropin, moschus. isomiiscon'). 



The solutions were fully saturated. This is, however, not necessary 

 for odorous substances with a strong tendency for tiansformation 

 such as eugenol, cressol, guaiacol, carvacrol etc. 



In glycerin solutions the phenomenon is of less frequent occurrence. 

 We demonstrated the absence of Tyndall's effect in a number of old 

 solutions in glycerin of odorous substances, which, when dissolved in 

 water, became colloidal within a few days. Also in a solution 

 in paraffin transformation occurs rarely. 



When there is hardly any solubility, Tyndall's effect cannot be 

 expected in the long run with odorous substances, but also, even when 

 e.g. fluorescence shows us that molecules are thrown into solution, 

 transformation to the colloidal state is sometimes lacking altogetliei-, 

 even when the solution has been standing for a long time. Such is 

 the case with heliotropin. Eugenol is the substance that, both in water 

 and in glycerin, attains a more intense colloidal condition than all 

 other odorous substances examined. Also in paraffin eugenol becomes 

 colloidal; anilin, in this solvent, still more so. 



Generall}^ speaking, odorous substances becoming intensely colloidal 



diffused light by means ot a Nicol prism in the large apparatus of ZsiGMOiNDi. 

 The solutions in glycerin, however, could not be taken up in an ordinary cuvette, 

 the stuff with which the quartz windows are fixed, being soluble in glycerin. In 

 this case we therefore used Zeiss' paraboloid condensor, or a Leitz' darkground- 

 condensor-cuvette. 



1) Kamerlingh Onnes and Keesom, Acad. Amst. 29 Feb. 190S. 



2) The list of odorous substances that are transformed spontaneously has since 

 been lengthened considerably. Also the alkaloids that become at length colloidal 

 in aqueous solutions, are very numerous. It is interesting to contrast with them 

 the crystalloid condition of nearly all solutions of antipyretioa (non-alkaloids). 



