250 PHYSIOLOGICAL PHYSICS. [Chap. xxn. 



the same density. In. Graham's own words, " the 

 diffusion must necessarily follow a diminishing 

 progression." Secondly, Graham found that tem- 

 perature affected the result, the rate increasing 

 apparently in direct proportion with the rise of 

 temperature. Thirdly, the rate of diffusion for 

 different salts was different. Each salt had its own 

 rate of diffusion. Thus, under the same conditions, 

 69 '32 grains of sulphuric acid diffused in the same 

 time occupied by 58 '68 of chloride of sodium, 51 '56 

 of nitrate of soda, 27 '42 of sulphate of magnesia, 

 26-74 of crystallised cane-sugar, 13 '24 of gum arabic, 

 and 3*08 of albumen. In another series of experi- 

 ments the following ratios were obtained : Chloride 

 of sodium, 100; hydrate of potash, 151 '9 3; ammonia 

 (10 per cent, solution), 70 ; alcohol, 75*74. " The most 

 remarkable result is the diffusion of albumen, which is 

 low, out of all proportion when compared with saline 

 bodies." A result of great interest is that " albumen 

 does not impair the diffusion of salts dissolved together 

 with it in the same solution, although the liquid 

 retains its viscosity." Thus, chloride of sodium, urea, 

 and sugar in solution were found to diffuse as freely 

 out of a solution of egg albumen as out of pure 

 water. 



A series of experiments was also made with 

 solutions of two salts, which could be mixed without 

 combining. They were found to diffuse separately, 

 but usually the salt of lower diffusibility had its rate 

 of diffusion somewhat lowered, so that the difference 

 in the rates of diffusion of the two different salts was 

 rather increased by mixture. This seemed to Graham 

 to afford a method by which different salts might be 

 separated from one another. Thus potash salts are 

 more diffusive than soda salts, and if a mixture of 

 both be put into a diffusion cell the potash salts will 

 diffuse more rapidly into the surrounding water, 



