EMULSOIDS 293 



substance suspended in a liquid continuous phase composed 

 of a much diluter solution. The term emulsoid, has been 

 adopted as indicating their general relation to the emulsions 

 which likewise are two phase systems produced from two 

 liquids which are immiscible. 



GENERAL PROPERTIES OF EMULSOIDS. 



The outstanding feature of the emulsoids as compared 

 with suspensoids is their much greater viscosity ; this fact, 

 however, is not surprising if the views put forward with 

 regard to their constitution are correct, since true emulsions are 

 known to have high viscosities, e.g. Mayonnaise %auce. The 

 viscosity of a solution varies both with the concentration and 

 the temperature ; it is liable to be influenced by a variety of 

 causes such as prolonged heating and by different methods of 

 treatment. In some cases the passage through a capillary 

 tube will alter the viscosity of a solution and in some instances 

 the viscosity will diminish spontaneously. Viscosity is, more- 

 over, considerably affected by the presence of dissolved salts, 

 being increased by sulphates, phosphates and citrates but 

 reduced by iodides or sulphocyanides. 



(a) Optical Properties. These are in many respects less 

 striking than those of the dispersoids since emulsoid sols, 

 although frequently opalescent or turbid, are not as a rule 

 highly coloured. The presence of the diffracting particles of 

 the disperse phase may, however, in some cases cause a 

 bluish opalescence as, for example, in a starch solution ; in- 

 deed, according to Bancroft,* the blue colour f of eyes and 

 feathers is caused by the same phenomenon. In common 

 with suspensoids, the emulsoids also exhibit the Tyndall 

 phenomenon. 



Examined under the ultramicroscope they also show 

 Brownian movement, but this is not so well defined as in 

 the case of suspensoids ; this is probably due to the fact 

 that there is not the same difference in refractive index 

 between the disperse and continuous phases in the case of the 



* Bancroft: " J. Phys. Chem.," 1919, 23, 356, 365. 



t According to Wo. Ostwald the blueness of the sky is similarly due to the 

 atmosphere being composed of matter in a disperse phase suspended in a con- 

 tinuous phase. 



