206 Mr. T. Graham on Liquid Diffusion applied to Analysis. 



solution. Fluid colloids appear to have always a pectous* modi- 

 fication, and they often pass under the slightest influences from 

 the first into the second condition. The solution of hydrated 

 silicic acid, for instance, is easily obtained in a state of purity, 

 but it cannot be preserved. It may remain fluid for days or 

 weeks in a sealed tube, but is sure to gelatinize and become in- 

 soluble at last. Nor does the change of this colloid appear to 

 stop at that point ; for the mineral forms of silicic acid, deposited 

 from water, such as flint, are often found to have passed, during 

 the geological ages of their existence, from the vitreous or colloidal 

 into the crystalline condition (H. Rose). The colloidal is, in 

 fact, a dynamical state of matter, the crystalloidal being the 

 statical condition. The colloid possesses energia. It may be 

 looked upon as the probable primary source of the force appear- 

 ing in the phenomena of vitality. To the gradual manner in 

 which colloidal changes take place (for they always demand time 

 as an element), may the characteristic protraction of chemico- 

 organic changes also be referred. 



A simple and easily applicable mode of effecting a diffusive 

 separation is to place the mixed substance under a column of 

 water, contained in a cylindrical glass jar of 5 or 6 inches in 

 depth. The mixed solution may be conducted to the bottom of 

 the jar by the use of a fine pipette, without the occurrence of 

 any sensible intermixture. The spontaneous diffusion, which 

 immediately commences, is allowed to go on for a period of 

 several days. It is then interrupted by siphoning off the water 

 from the surface in successive strata, from the top to the bottom 

 of the column. A species of cohobation has been the consequence 

 of unequal diffusion, the most rapidly diffusive substance being 

 isolated more and more as it ascended. The higher the water 

 column, sufficient time being always given to enable the most 

 diffusive substance to appear at the summit, the more completely 

 does a portion of that substance free itself from such other less 

 diffusive substances as were originally associated with it. A 

 marked effect is produced even where the difference in diffusi- 

 bility is by no means considerable, such as the separation of 

 chloride of potassium from chloride of sodium, of which the 

 relative diffusibilities are as 1 to 0841. Supposing a third 

 metal of the potassium group to exist, standing above potassium 

 in diffusibility as potassium stands above sodium, it may be 

 safely predicated that the new metal would admit of being 



* J1t]ktos, curdled. As fibrine, caseine, albumen. But certain liquid 

 colloid substances are capable of forming a jelly and yet still remaining 

 liquefiable by heat and soluble in water. Such is gelatine itself, which 

 is not pectous in the condition of animal jelly, but may be so as it exists 

 in the gelatiniferous tissues. 



