SECT. in. A THOL YSIS. 1 1 1 



in water, a substance so hard that no pure aqueous 

 solution of it had ever^been obtained. Many other 

 crystalline substances^besides quartz can exist both in 

 the colloid and crystalloid states. 



All colloid substances are characterized by non-crys- 

 talline habits, low diffusibility, chemical inertness, high 

 atomic weight, and above all by their mutability. The 

 aqueous solution of quartz is limpid and liquid, even if 

 it contains 14 per cent, of silica, but after a time it 

 becomes opalescent, viscous, and ultimately sets into a 

 firm insoluble jelly, capable however of solution by 

 chemical means. This jelly gradually shrinks, exudes 

 pure water, and when perfectly dry it forms a glassy, 

 transparent, but not anhydrous substance, and the 

 residue left by ignition has a specific gravity of 2-2, that 

 of crystallized silica being 2*6. 



Mr. Graham has obtained many pure aqueous solu- 

 tions of organic and inorganic matter, most of them 

 being unstable. Ice near or at its melting point is 

 believed to be a colloid body, consequently it is unstable 

 and resembles a firm jelly, having a tendency to rend 

 and recombine. ' The constant intervention of colloid 

 septa in so many of the phenomena of animal and 

 vegetable life gives to the subject of dialysis a high 

 physiological interest, and it will doubtless exercise an 

 important influence on the progress of physiological 

 research.' 3 



Subsequently to these researches Mr. Graham pub- 

 lished a memoir on a new method of analysing gases 

 which he had called atmolysis. The memoir may be 

 regarded as consisting of four parts, the first of which is 

 preliminary, being on the reciprocal diffusion of gases 

 through porous plates. The next three parts relate to 

 effusion, or the passage of gases under constant pressure 



3 Lectures of much interest by Dr. "William Odling in the Chemical News 

 of 1862. 



