198 DISCUSSION OF EVIDENCE. 



This answer may not at first appear to be self-evident, but a moment's 

 thought will show its general correctness. The whole science of chem- 

 istry is primarily a branch of the science of solutions in the broad 

 sense of that term. By solutions is meant not simply solutions in 

 liquids as the solvent, but solutions in gases and in solids as well; and 

 not simple solutions at ordinary temperatures, but also at elevated 

 temperatures. If we think of chemical reactions in general, we will 

 realize what a small percentage of them takes place out of solution. 

 Therefore, the nature of solutions is absolutely fundamental for chem- 

 istry. This applies not simply to general chemistry, including the 

 chemistry of carbon, but also to physiological chemistry, which deals 

 almost entirely with solutions in one solvent or another. 



When we turn to physics we find solutions not playing as prominent 

 a role as in chemistry, but nevertheless coming in in many places. 

 The primary cells, secondary cells, electrolysis, polarization, diffusion, 

 viscosity, surface-tension, are all phenomena in which the physicist is 

 interested, and all depend for their existence upon solution. 



When we turn to the biological sciences we find that solution is 

 almost as important as for chemistry. Take animal physiology ; here we 

 have to deal very largely with solution in the broad sense of that term. 

 The same remark applies to physiological botany; and solutions are 

 very important for both animal and vegetable morphology, especially 

 in their experimental developments. Bacteriology is fundamentally 

 connected with solutions, and pharmacology is based upon solutions 

 either without or within the body of the animal. 



Solution in the broad sense is as fundamental for geology as for 

 chemistry. The igneous rocks were solutions of one molten mass in 

 another; and sedimentary deposits came down for the most part from 

 solutions true or colloidal in water. The minerals crystallized out from 

 solutions, and solutions of various substances, such as carbon dioxide, 

 are to-day weathering the rocks and continually changing the appear- 

 ance of the face of the globe. 



An examination of facts such as those referred to above will show 

 that the relation of physical or general chemistry to solutions is the 

 prime reason why physical or general chemistry is so closely related 

 to so many other branches of natural science. This alone would show 

 the importance of a true and comprehensive theory of solutions, not 

 alone for physical or general chemistry, but for the natural sciences in 

 general. 



