592 



APPENDIX 



phenomenon, which is exhibited when toxins and antitoxins are 

 mixed together, is probably due to the fact that precipitation de- 

 pends on inequality and irregular distribution of electric charges, 

 a condition which becomes established when the electrolyte is sud- 

 denly added, but not so when it is gradually added." This phe- 

 nomenon is of considerable importance in immunology. 



Charged 

 .suipfinsoid 



dehydration b>j alcohol 



ptecipitatincj 

 particle 



\jnchar$ei 

 emulsoid 



Fig-. 27. — Factors involved in dispersion and precipitation of colloids. (After 

 Kruyt and Van Klooster, Colloids, John Wiley and Sons, 1930.) 



Protective Action of Colloids. — From the preceding discussion 

 it can be seen that emulsoids are much more resistant to the 

 precipitating action of electrolytes than suspensoids. This is due 

 to their water layer. If the dispersed particles of a suspensoid 

 like colloidal gold, which is quite sensitive to the precipitating 

 power of electrolytes, can be made to adsorb a film of a stable 

 emulsoid around each particle, then the suspensoid will be pro- 



