Mr. T. Graham on Liquid Diffusion applied to Analysis, 375 



water, about 32° C, for twenty-four hours. The whole was 

 then thrown upon a dialyser for an equal time. Arsenious acid 

 diffused out so free from colloidal matter that the action of 

 reagents was not interfered with. A high temperature in di- 

 gesting the intestines is quite unnecessary, and appeared indeed 

 to increase the difficulty of diffusing out the arsenious acid 

 afterwards. 



The tartrate of potash and antimony, mixed in the small pro- 

 portion of ■ , ., \ , th, with defibrinated blood and with milk, 



1 10,0 / m • ■ ' 



was separated by dialysis quite as effectually as the arsenious 

 acid above. 



Strychnine also was separated from organic fluids in the same 

 manner, a small addition of hydrochloric acid being first made to 

 the fluid on the dialyser. 



Dialysis, then, appears of general application in the preparation 

 of a liquid for examination by chemical tests, whether the poison 

 looked for be mineral or organic. All soluble poisonous sub- 

 stances, whatever their origin, appear to be crystalloids, and 

 accordingly pass through colloidal septa. 



7. Colloidal Condition of Matter. 



I may be allowed to advert again to the radical distinction 

 assumed in this paper to exist between colloids and crystalloids 

 in their intimate molecular constitution. Every physical and 

 chemical property is characteristically modified in each class. 

 They appear like different worlds of matter, and give occasion to 

 a corresponding division of chemical science. The distinction 

 between these kinds of matter is that subsisting between the 

 material of a mineral and the material of an organized mass. 



The colloidal character is not obliterated by liquefaction, and 

 is therefore more than a modification of the physical condition 

 of solid. Some colloids are soluble in water, as gelatine and 

 gum-arabic; and seme are insoluble, like gum-tragacanth. 

 Some colloids, again, form solid compounds with water, as gela- 

 tine and gum-tragacanth, while others, like tannin, do not. In 

 such points the colloids exhibit as great a diversity of property 

 as the crystalloids. A certain parallelism is maintained between 

 the two classes, notwithstanding their differences. 



The phenomena of the solution of a salt or crystalloid pro- 

 bably all appear in the solution of a colloid, but greatly reduced 

 in degree. The process becomes slow, — time, indeed, appearing 

 essential to all colloidal changes. The change of temperature, 

 usually occurring in the act of solution, becomes barely percept- 

 ible. The liquid is always sensibly gummy or viscous when 

 concentrated. The colloid, although often dissolved in a large 

 proportion by its solvent, is held in solution by a singularly 



