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



The experiments were conducted in the absence of light, and 

 there is no reason to believe that the iodine acted chemically 

 upon the alcohol. The diffusion is more advanced in the iodine 

 than in the acetate of potash, but in both is moderate in amount, 

 confirming the early experiments with phials, which appeared to 

 show that the diffusion process was several times slower in 

 alcohol than in water. The small quantities of iodine found in 

 each of the six superior strata are nearly equal, and were no 

 doubt accidentally elevated by the mobility of this fluid, arising 

 from its high dilatability by heat compared with that of water at 

 the same low temperature. The diffusion may be considered 

 then as confined to the nine lower strata, and considerably re- 

 sembles that of sugar in water for eight days. 



The diffusion of acetate of potash is still less advanced than 

 that of iodine, and is probably confined to the six lower strata, 

 the salt found in the higher strata presenting in its distribution 

 the appearance of having been carried there by a movement of 

 the fluid consequent upon heat-dilatation, and not by diffusion. 

 The diffusion of acetate of potash in alcohol observed during 

 seven davs approximates to that of sugar in water during six 

 days (Table IV.). 



I now proceed to observations of the simultaneous diffusion of 

 two substances in the same fluid. The great object of this class 

 of experiments was to separate salts of unequal diffusibility, and 

 to test the application of diffusion as an analytical process. A 

 mixture of two salts being placed at the bottom of the jar, it 

 may be expected that the salts will diffuse pretty much as they 

 do when they are diffused separately; the more diffusive salt 

 travelling most rapidly, and showing itself first and always most 

 largely in the upper strata. The early experiments of diffusion 

 from phials had shown indeed that inequality of diffusion is in- 

 creased by mixture, and the actual separation is consequently 

 greater than that calculated from the relative diffusibilities of 

 the mixed substances. Chlorides of potassium and sodium diffuse 

 nearly in the proportion of 1 to - 841, according to the earlier 

 experiments. They may afford, therefore, the means of observing 

 the amount of separation that may be produced by a very mode- 

 rate difference in diffusibility. A mixture of 5 grammes of each 

 salt in the usual 100 cub. cent, of water was diffused. 



