JACOBUS HENRICUS VAN'T HOFF. ix 



the real meaning of phenomena, and that foresight that enables one 

 to see relations from very meager and imperfect data, which are 

 characteristic of the highest genius, \'an't Hofif saw from the few 

 osmotic pressure measurements of Pfefifer the relations between solu- 

 tions and gases — the laws of gas pressure applied to the osmotic pres- 

 sure of solutions. In a word, we could deal with solutions as with 

 gases." 



This raises the question why is it so important to be able to deal 

 with solutions as with gases? We know more about matter in the 

 gaseous state than in any other state of aggregation. There we can 

 apply the laws of thermodynamics. A^an't Hofif applied the law's of 

 thermodynamics to solutions and gave us for the first time a satis- 

 factory thermodynamical theory of dilute solutions. 



The question, however, still remains, why is a satisfactory, rigid 

 theory of solutions of such importance? This becomes almost self- 

 evident if we will consider what solutions mean for science in general. 



The whole science of chemistry is hardly more than a branch of 

 the science of solutions in the broader science of that term. Solu- 

 tions are fundamental to nearly all of the biological sciences, experi- 

 mental botany, zoology, physiology, pharmacology and pathology, and 

 geology is as dependent upon solutions as chemistry. 



In the light of these facts it is obvious that the science of solu- 

 tions is fundamental for natural science in general, and the placing 

 of solutions upon an exact, scientific basis might almost be regarded 

 as the initial step tow^ards rendering chemistry, geology and the bio- 

 logical sciences exact branches of science. 



This is what \ an't Hoft' did in pointing out the relations between 

 solutions and gases. He, however, did not stop here. The laws of 

 gases apply to the osmotic pressures of solutions of nonelectrolytes 

 only, /. r., to solutions of substances which do not conduct the cur- 

 rent. These laws do not apply to the osmotic pressures of a single 

 electrolyte, and since all acids, bases and salts are electrolytes the 

 gas laws do not apply to solutions of the most common substances 

 in chemistry. \"an't Hoff saw clearly these exceptions to the rela- 

 tions that he had discovered and pointed them out in his great paper 

 above referred to. It is well known that it was to explain these 



