80 DISPERSE SYSTEMS 



form an emulsoid what really results is a dispersion of a solution 

 of water in A, throughout a solution of A in water. The stability 

 of such a system will depend in great measure on the viscosity of 

 the intermicellar liquid. The viscosity depends on the concen- 

 tration of the more viscous A in the less viscous water. The 

 range of viscosity making for stability will be bounded on the one 

 hand by a certain minimum and on the other hand by a certain 

 maximum concentration of water in the continuous phase. 



Protective action of Emulsoids. 



Many emulsoids when added in comparatively minute quantities 

 to suspensoids prevent the coagulation of the suspensoids by 

 electrolytes. As a matter of fact, each emulsoid which exhibits 

 this property has a characteristic protective power which may 

 be used as a definite factor for the identification of the colloid. 

 The suspensoid generally used in the test is colloidal gold. Zsig- 

 mondy, who devised the method, defines the " gold number " 

 as the number of milligrams of an emulsoid which are just suffi- 

 cient to prevent 10 c.c. of a bright red gold sol (prepared under 

 certain specified conditions) from changing into violet or shades 

 of violet after the addition of 1 c.c. of 10 per cent, sodium 

 chloride solution (Part II.). 



He divides colloids into four classes according to their " gold 

 number," viz. : 



TABLE XIII. 



The general opinion seems to be that the emulsoid forms a 

 pellicle round each suspensoid particle and prevents coagulation, 

 either (1) because, as we have seen, emulsoids are less sensitive 

 to the precipitating action of electrolytes and the compound 

 particle is endowed with an emulsoid coat ; (2) because the 

 electrolyte does not come in contact with the suspensoid particle 

 and does not neutralise its electric charge, or (3) merely by offering 

 a material obstacle to the coalescence of the particles. 



The fluids of the body contain two colloidal substances of 

 peculiar interest. Albumin and globulin are both emulsoids, 



