94 



DISPERSE SYSTEMS 



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 XV 



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 the globulins are emulsoids, 

 but they differ physically in at least three respects summarised 

 below. 



TABLE XVI 



Albumin. 



Sol in water. 



(Sol in 5 per cent. NaCl.) 

 Not ppt. by \ sat. (NH4)2SO.i. 

 Protects suspensoids. 



Globulin. 



In sol in water. 



(Sol in 5 per cent. NaCl.) 

 Ppt. by i sat. (NHJoSOj. 

 Ppts. suspensoids. 



Albumin has a protective action on gold sol, while globulin 

 acts almost as if it were a suspensoid. The proportions of albumin 

 and globulin in the various body fluids are practically invariable 

 in health, but duriim the course of various diseases the balance 

 is u])sc't. If the globulin content is increased relatively to the 

 albumin, then the body fluid will lose a portion of its protective 



