[ 254 ] 



XXX. On the Diffusion of Liquids. 

 By Thomas Graham, F.R.S., F.CS. 



[Continued from p. 198.] 



5. Separation of Salts of different Bases by Diffusion. 



IT was now evident that inequality of diffusion supplies a 

 method for the separation, to a certain extent, of some salts 

 from each other, analogous in principle to the separation of 

 unequally volatile substances by the process of distillation. 

 The potash salts appearing to be always more diffusive than 

 the corresponding soda salts, it follows, that if a mixed solu- 

 tion of two such salts be placed in the solution phial, the pot- 

 ash salt should escape into the water atmosphere in largest 

 proportion, and the soda salt be relatively concentrated in the 

 phial. This anticipation was fully verified. 



(1.) A solution was prepared of equal parts of the anhy- 

 drous carbonates of potash and soda in 5 times the weight of 

 the mixture of water. Diffused from a small thousand-grain 

 phial of 1*1 inch aperture, into 6 ounces of water, for nine- 

 teen days, at a temperature above 60°, it gave a liquid of den- 

 sity 1*0350, containing a considerable quantity of the salts. 

 Of these mixed salts, converted into chlorides by the addition 

 of hydrochloric acid, 9*39 grs., being treated with bichloride 

 of platinum in the usual manner, gave 19*39 grs. of the double 

 chloride of platinum and potassium, equivalent to 5*91 grs. of 

 chloride of potassium ; and left in solution 3*44 grs. of chlo- 

 ride of sodium : loss 0*04 gr. These chlorides represent 5*46 

 grs. of carbonate of potash and 3*12 grs. of carbonate of soda. 

 The salts actually diffused out were therefore in the proportion 

 of— 



Carbonate of soda ..... 36*37 

 Carbonate of potash 63*63 



100*00 



(2.) In another similar experiment from a six-ounce phial 

 into S~ ounces of water, the liquid of the water-jar, after twenty- 

 five days' diffusion, contained the two carbonates in nearly the 

 same proportions as before, namely — 



Carbonate of soda 35*2 



Carbonate of potash 64*8 



100*0 



(3.) A partial separation of the salts of sea- water was effected 

 in a similar manner. 



The sea-water (from Brighton) was of density 1*0265. One 



