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SCIENCE PROGRESS. 



number of ions into which it can be resolved. Thus the 

 effect of an active molecule of KC1 is twice that of an in- 

 active one, and the effect of a molecule of H 2 S0 4 (which gives 

 two H ions and one S0 4 ion) is, when in a state of ionisa- 

 tion, three times as great as that of a non-electrolyte. If, 

 then, in a certain solution, we have ;// inactive and n active 

 molecules, each of the latter giving k ions, the total 

 osmotic pressure will be proportional to m + kn, whereas, if 

 there were no ionisation, it would be m+u. Let us call the 

 ratio of the actual to the normal osmotic pressure 2, then 



m + ku m + n + kn — n 



1 = 



But 



m + 11 

 n 



= 1 + 



;/ 



(k- ,). 



m + ;/ 111 + n 



is the fractional number of molecules which 



m 4- ;/ 



is at any moment ionised, i.e., the coefficient of ionisation, o, 

 or /Li'/m^, so that it can be found by conductivity measure- 

 ments, and we get 



i = I + {k - l)a. 



By placing the values of i thus calculated by the side of 

 those directly observed from the freezing point, we get the 

 following comparison : — l 



Another method of tracing the connection between the 

 two effects is to compare the coefficient of ionisation calcu- 



1 Zeits.fiirphysikal. Chemie, ii., p. 491, 1887. 



