346 Prof. Graham on the Diffusion of Liquids, 



falling from 55°*2 to 53° during the longer period, but without 

 any injurious oscillation. 



From eight cells, evaporated two together, the sulphate of 

 magnesia obtained was 6*12, 6*12, 6*04 and 6*03 grs. ; mean 

 6*08 grs., or 3*04 grs. for one cell. 



The sulphate of potash gave from eight cells, in experi- 

 ments already detailed, a mean result of 5*84 grs. of salt for 

 two cells, or 2-92 grs. for one cell. The diffusion is in the pro- 

 portion of 100 sulphate of potash to 104*11 sulphate of mag- 

 nesia, the times being as 1 to 2 for the two salts respectively. 



From these two series of experiments, it appears that, at 

 54°, sulphate of magnesia has nearly, if not exactly, half the 

 diffusibility of sulphate of potash, and consequently one-fourth 

 of that of hydrate of potash. Or, the times of equal diffusion 

 for these three salts appear to be 1, 2 and 4. The squares of 

 these times and the solution densities are 1, 4 and 16. Hy- 

 drate of potash may possibly therefore have the same relation 

 to sulphate of magnesia in solution, density and diffusibility, 

 that hydrogen gas has to oxygen gas. 



(3.) A two per cent, solution of sulphate of magnesia, dif- 

 fused for fourteen days, gave at 53 0, 9, for two pairs of cells, 

 9*57 and 10*00 grs. of salt, of which the mean is 9*79 grs., 

 or 4*85 grs. for one cell. 



A similar solution of sulphate of potash diffused for seven 

 days gave a mean result of 4*97 grs. of salt for one cell, at 

 54°*2, as already stated. The result is a diffusion of 100 sul- 

 phate of potash to 97*59 sulphate of magnesia. 



(4.) A four per cent, solution of sulphate of magnesia, dif- 

 fused for fourteen days, gave at 53°'7, in two pairs of cells, 

 18*00 and 18*20 grs. of salt; mean 18*10 grs. for two cells, 

 or 9*05 grs. for a single cell. 



A similar solution of sulphate of potash, diffused for seven 

 days at 54°*2, gave a mean result of 9*30 grs. of salt for a single 

 cell, as already stated. This is a diffusion of 100 sulphate of 

 potash to 97*4 sulphate of magnesia. 



The diffusion of the 2 and 4 per cent, solutions of sulphate 

 of magnesia is so nearly equal to the diffusion of the same 

 proportions of sulphate of potash in half the time, that they 

 may be considered as supplying additional support to the 

 assumed relation between the diffusibilities of these salts. 



1 may rdd, that a 4 per cent, solution of anhydrous sulphate 

 of zinc was diffused for fourteen days, simultaneously with the 

 similar solution of sulphate of magnesia, and of course at the 

 same temperature of 53°*7. Two cells, evaporated two toge- 

 ther, gave 17*40 and 17'36 grs. of ignited sulphate of zinc; 

 mean 17*38 grs. The salt remained, after ignition, entirely 



