186 Dr. C. V. Burton on Endless Availability ; and on a 



Temp, of thermometer, which has lain 



beside the apparatus for 14 days . . =14*2 



Temp, of solutions in A and in . . . =14' 2 



Temp, of solutions after mixing . . . =15*4 



Rise of temperature =1*2 



Nov. 10. Crystals, apparently about equal to the original 

 crystal in A, have been deposited. 



Thus we can perform a complete cycle of changes. Starting 

 with saturated solution and crystals of sodium sulphate in the 

 dialyser, at the temperature of surrounding objects, an iso- 

 thermal change first takes place. Next the separated portions 

 of the solutions are mixed, and may be maintained under 

 adiabatic conditions till all possible crystallization has taken 

 place, evaporation being of course excluded. The result is a 

 considerable rise of temperature, with corresponding gain of 

 motivity ; and finally, when the liquid has been cooled down 

 (with further deposition of crystal) to the initial temperature, 

 we have come back to precisely the conditions with which we 

 started — a saturated solution and crystals of sodium sulphate, 

 at the temperature of surrounding objects. 



Now consider what is the action of the dialysing membrane. 

 According to the view of Arrhenius, dissociation and recom- 

 bination are continually occurring amongst the molecules of 

 the solution, each dissociation being accompanied by an 

 absorption of heat, and each recombination by an equal evo- 

 lution of heat. By filtering such a solution through a mem- 

 brane, the equilibrium of these processes is disturbed. The 

 various chemical constituents will pass through at different 

 rates, thus giving rise to chemical separation and (isothermal) 

 absorption of heat*. The membrane then plays the part of a 

 sieve : it does not really cause dissociation ; it only effects a 

 selective distribution of molecules already dissociated. If 

 reliance could be placed in the constancy of a dialysing mem- 

 brane, and if the composition, temperature, and level of the 

 liquid above the membrane were also maintained constant, an 

 analysis of the portion which passes through might furnish 

 some conclusions as to the amount of dissociation in the 

 solution. It would be interesting to compare such results 

 with the data afforded by measurements of electrolytic con- 

 ductivity. 



Experiment II.— The acid sodium sulphate being more 

 soluble than the normal sulphate, the more acid liquid which 



* The solution remaining in the dialyser is alkaline, and therefore non- 

 saturated ; hence the crystal dissolves. 



