CHAPTER VII. 

 METHODS OF COLLOID RESEARCH. 



A FIELD of research extending as does colloid chemistry into so 

 many other branches of science must be served by countless methods. 

 Purely chemical as well as physical and biological methods which 

 the investigator of colloids utilizes in his studies, have been so well 

 developed and so thoroughly described in technical literature, that it 

 is needless to discuss them more fully here. 



There are, however, several methods which are peculiar to colloid 

 investigation, and we shall consider them here. Unfortunately, the 

 limits of their usefulness are as yet unestablished; for some one to 

 establish them would be highly desirable. 



In discussing the following methods, I have not sought complete- 

 ness but have considered only those which have proved practical; 

 I have personally tested most of them. 



To determine whether a solution of a substance is colloidal in 

 character it must be tested by dialysis, ultrafiltration or diffusion. 



Dialysis is a purely qualitative method which determines whether 

 or not a substance is colloidal in character, i.e., whether or not it 

 consists of large particles. 



Ultrafiltration in most cases may be used instead of dialysis; it 

 works much more rapidly and above all permits, in addition, quan- 

 titative experiments, and consequently has a much broader utility. 



Both methods serve to separate colloids from crystalloids. This 

 separation occurs with dialysis if the water surrounding the dialyzer 

 is frequently renewed; it occurs with ultrafiltration, provided the 

 substance on the funnel is washed repeatedly, as in an ordinary filter. 



Diffusion is an excellent quantitative method for the investigation 

 of particle size. The performance of diffusion experiments is, how- 

 ever, a difficult matter, because even variations in temperature may 

 cause material errors. 



Dialysis. 1 



The most varied apparatus and membranes may be used for 

 dialysis. An apparatus described in most textbooks and used in many 



1 An exhaustive description of all known methods of dialysis is given by E. 

 ZUNZ in Abderhalden's Handb. d. biochem. Arbeitsmethoden 3, pages 165-189 

 and Supplement, pages 478-485. 



