899 



When two salts are mixed in the solution-cell, they diffuse out 

 into the water atmosphere separately and independently of each 

 other, according to their individual diffasibilities. This is quite ana- 

 logous to what happens when mixed gases are diffused into air. An 

 important consequence is, that in liquid diffusion we have a new 

 method of separation or analysis for many soluble bodies, quite ana^ 

 logons in principle to the separation of unequally volatile substances 

 in the process of distillation. Thus, it was shown that chlorides 

 diffuse out from sulphates and carbonates, and salts of potash from 

 salts of soda; and that from sea-water the salts of soda diffuse out 

 into pure water faster than the salts of magnesia. The latter cir- 

 cumstance was applied to explain the discordant results which have 

 been obtained by different chemists in the analyses of the water of 

 the Dead Sea, taken near the surface ; the different salts diffusing 

 up into the sheet of fresh water, with which the lake is periodically 

 covered, with unequal velocity. 



It was further shov/n that chemical decompositions may be pro- 

 duced by liquid diffusion ; the constituents of a double salt of so 

 much stability as common alum being separated, and the sulphate of 

 potash diffusing in the largest proportion. In fact, the diffusive force 

 is one of great energy, and quite as capable of breaking up com- 

 pounds as the unequal volatility of their constituents. Many empiri- 

 cal operations in the chemical arts, it was said, have their foundation 

 in such decompositions. 



Again, one salt, such as nitrate of potash, will diffuse into a solu- 

 tion of another salt, such as nitrate of ammonia, as rapidly as into 

 pure water; the salts appearing mutually diffusible, as gases are 

 known to be. 



Lastly, the diffusibilities of the salts into water, like those of the 

 gases into air, appear to be connected by simple numerical relations. 

 These relations are best observed when dilute solutions of the salts 

 are diffused from the solution-cell, such as 4, 2 or even 1 per cent, 

 of salt. The quantities diffused in the same time from 4 per cent, 

 solutions of the three salts, carbonate of potash, sulphate of potash 

 and sulphate of ammonia, were 10'25, 10*57 and 10°51 grains re- 

 spectively ; and a similar approach to equality was observed in the 

 ] , 2, and 6f per cent, solutions of the same salts. It also held at 

 different temperatures. The acetate of potash appeared to coincide 

 in diffusibility with the same group, and so did the ferrocyanide of 

 potassium. The nitrate of potash, chlorate of potash, nitrate of am- 

 monia, chloride of potassium and chloride of ammonium formed an- 

 other equi-diffusive group. The times in which an equal amount of 

 diffusion took place in these two groups appear to be as 1 for the 

 second to 1'4<142 for the first, or as J to the square root of 2. Now 

 in gases, the squares of the times of equal diffusion are the densities 

 of the gases. The relation between the sulphate of potash and nitrate 

 of potash groups w^ould therefore fall, to be referred to the diffusion 

 molecule or diffusion vapour of the first group having a density re- 

 presented by 2, while that of the second group is represented by J . 



The corresponding salts of soda appeared to fall into a nitrate and 



1* 



