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THE NEW YORK JOURNAL OF PHARMACY 



did not pass through were usually amor- 

 phous or glue-like, so he divided all mat- 

 ter into two general classes : Crystalloids 

 and Colloids (from colla, glue). 



But Graham made another important 

 discovery. He found that certain sub- 

 stances, which were said to be insoluble, 

 could be obtained in so-called pseudo- 

 solutions (a term proposed by Franceschi 

 di Selmi in the forties). Graham pre- 

 pared solutions of Ferric Hydroxide, 

 Chromium Hydroxide and others, and 

 found that they did not dialyse, so he gave 

 them the name "Colloidal Solutions,"' or 

 "Sols," a term which is now accepted and 

 used for a colloidal solution. It would 

 lead too far to go into all of Graham's 

 investigations ; simply let me state that 

 they laid the foundation for the colloid 

 chemistry of to-day. After Graham, 

 work on colloidal substances was done 

 by others, but little importance was at- 

 tached to it ; the theoretical and practical 

 researches of organic and inorganic 

 chemistries dominated the scientific 

 world. Whatever chemical change or 

 phenomenon which could not be ex- 

 pressed by a formula was not considered 



, Dispersoids — 



vv(jrtli investigation. Interest in the sub- 

 ject was re-awakened, however, in the 

 late nineties, when Bredig succeeded in 

 preparing colloidal solutions of heavy 

 metals by the aid of the electric spark. 



The actual impetus to the work on 

 colloids, however, was given by the in- 

 vention of the Ultra-Microscope by Zig- 

 monody and Siedentopf in 1905. 



Our present view of the nature of col- 

 loids is diametrically opposed to that of 

 Graham. He distinguished two worlds — 

 the Crystalline and th6 Colloid worlds. 

 Our present accepted view is, that there 

 is only one world and that the colloid 

 state can be assumed by any substance, 

 solid or liquid, under appropriate con- 

 ditions. 



A general definition for a colloidal so- 

 lution or a "sol" is this : A colloid is 

 any solid, liquid or gaseous substance in 

 a certain state of subdivision, or disper- 

 sion, in another solid, liquid or gaseous 

 substance. 



A substance which is subdivided or 

 dispersed is called a "Dispersoid." In 

 order to illustrate the above definition 

 of colloid, I ask you to kindly look at 

 (Jstwald's Schema: 



Coarse Dispersions 

 Suspensions 

 Emulsions 

 Size of particles 

 larger than .if^ 



Colloids Molecular 



Dispersions 



Less than imm 



O.IM-IMM 



\\\ Increasing dispersion \ 



/77 7 



Ionic 

 Dispersions 



There are. of course, transition states 

 between the above dispersions. 



A colloidal solution, or "sol," consists 

 of at least two substances, the dispersoid 

 and the dispersion medium ; a colloidal 



solution is, therefore, a "di-phasic heter- 

 ogeneous system." 



Inasmuch as solids, as well as liquids 

 and gases, can form part of a colloidal 

 system, we distinguish nine difi:"crent 

 cases, as follows : 



