CHAPTER Til 

 LIQUID SOLUTIONS 



" Solutions are homogeneous mixtures — mixtures which 

 allow no separation of their components by mechanical 

 means. The ability of gases to form such mixtures is un- 

 limited, that of liquids is limited."' Solid solutions also 

 exist, but have not yet been shown to play any part in 

 physiology; therefore they need not be considered here. 

 Gas mixtures have already been discussed. There remains, 

 then, only the subject of liquid solutions — a very important 

 subject in the study of physiology. 



I. SOLUTIONS OF LIQUIDS IN LIQUIDS 



Not nearly all liquids are readily miscible to form solu- 

 tions. Many are nearly — perhaps quite — insoluble in one 

 another. Again, many liquids are mutually soluble in all 

 proportions (e. g., water and alcohol) ; others are so only 

 within certain limits. 



When a mixture of two liquids is considered as a solu- 

 tion, the liquid which preponderates is called the solvent 

 and the other the solute. If such a solution were brought 

 into contact with a mass of the pure solvent, diffusion of the 

 solute would take place into the pure solvent until the solute 

 were uniformly distributed throughout both layers. At the 

 same time the pure solvent would diffuse into the solution. 

 Of course, the interchange of particles between two such 

 layers would not cease when uniformity of constitution had 

 been attained throughout; it would still go on, but would 

 cease to be apparent, having become simply the continuous 

 motion of the particles composing the uniform mixture. At 



1 Ostwald-Walkee, Outlines of General Chemietry (LoDdon, 1895), p. 117. 



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