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HARRY C. JONES 



them. Let us, therefore, be very careful to distinguish between 

 the fact that gas pressure and osmotic pressure under comparable 

 conditions are equal, and what we might imagine to be true, but 

 which has not the slightest foundation in fact, viz., that gas pres- 

 sure and osmotic pressure have a common cause. 



The three most fundamental laws of gas pressure, then, apply 

 to the osmotic pressure of solutions. But of what importance 

 is this generalization or the discover}^ of such relations? 



Let us leave this question for a moment, until we have looked a 

 little more closely and thoroughly into the properties of solutions 

 in general. That the laws of gas pressure apply to the osmotic 

 pressure of solutions of substances such as cane sugar is obvious 

 from what has been said. But this is not the whole truth. 

 Solutions of acids, bases and salts exert osmotic pressures that are 

 too great in terms of the gas laws. But acids, bases and salts 

 are those substances which, when dissolved in water, conduct the 

 electric current. These are the electrolytes, while cane sugar is 

 a typical non-electrolyte. Electrolytes, then, in general have 

 osmotic pressures that do not obey the laws of gas pressure, but 

 are too great in terms of these laws. WTiat does this mean? 



The answer to this question is the theory of electrolytic dis- 

 sociation proposed in 1887 by .Aj-rhenius, and the paper announc- 

 ing this theor}' was published in the same volume of the Zeit- 

 schrift fiir phj^sikahsche Chemie (vol. i) as Van't Hoff's paper 

 on the relations between gas pressure and osmotic pressure. 



The theory of electrolytic dissociation, as is well known, states 

 that acids, bases and salts, when dissolved in a dissociating sol- 

 vent like water, break down into charged parts or ions, and that 

 it is these parts which are the active agents chemically. The 

 evidence for the general correctness of this theory comes from so 

 many independent sources, and is now so overwhelming, that I 

 know of no productive chemist who fails to accept it at least as a 

 basis of work. 



It would lead us too far here, and it would be quite superfluous, 

 to attempt to present even a few of the many lines of e\ddence 

 bearing on this theory, in the brief time at my disposal. Suffice 

 it to say that this theory when taken with the relations between 



