Mr. T. Graham on Liquid Diffusion applied to Analysis. 291 



Diffusion of a crystalloid thus appears to proceed through a firm 

 jelly with little or no abatement of velocity. With a coloured 

 crystalloid, such as bichromate of potash, the gradual elevation of 

 the salt to the top of the jar is beautifully illustrated. On the 

 other hand, the diffusion of a coloured colloid such as caramel, 

 through the jelly, appeared scarcely to have begun after eight 

 days had elapsed. The diffusion of a salt into the solid jelly 

 may be considered as cementation in its most active form. 



Numerous experiments were made on the diffusion of crystal- 

 loids through various dialytic septa, such as gelatinous starch, 

 coagulated albumen, gum-tragacanth, besides animal mucus and 

 parchment-paper, which all tended to prove how little the dif- 

 fusive process was interfered with by the intervention of colloid 

 matter. Salts appeared to preserve their usual relative diffusi- 

 bility unchanged. The same partial separation of mixed salts 

 was observed as in the water-jar. With a mixture, for instance, of 

 equal parts of chlorides of potassium and sodium in the dialyser, 

 the first tenth part of the mixture which passed through was 

 found to consist of 59*17 per cent, of chloride of potassium and 

 40*83 per cent, of chloride of sodium. Double salts also, such 

 as alum, and the sulphate of copper and potash, which admit of 

 being resolved into pairs of unequally diffusive salts, were largely 

 decomposed upon the dialyser, as they are in the water-jar. The 

 effect of heat in promoting diffusion appeared, however, to be 

 diminished in dialysis, at least with a parchment-paper septum. 

 Thus the diffusion from a 2 per cent, solution from chloride of 

 sodium in a constant period of three hours was, — 



At 10 

 At 20 

 At 30 

 At 40 



0-738 grm. 

 0*794 grm. 

 0*892 grm. 

 1*017 grm. 



Ratio. 

 1 



1-07 

 1-20 

 1-37. 



The rate of diffusion in water alone, without the septum, 

 would have been doubled by an equal rise of temperature instead 

 of being increased one-third only as above. 



Fig. 3.— Bulb Dialyser. 



The small glass bell-jar (figs. 3, 4) formerly used as an osmometer, 



