THE PROBLEMS OF SOLUTION 123 



them disintegrate and dissolve in presence of 

 water and other liquids indicates that some inter- 

 action between them and their solvent must occur. 

 It seems likely that the forces which are involved 

 in crystalloid solution are of the nature of those 

 classed as chemical or molecular, while, when 

 colloids dissolve, the actions between solvent and 

 solute are conditioned also by the phenomena 

 studied under the names of capillarity and surface 

 tension. It is not likely that any sharp line of 

 demarcation can be drawn ; though, as the size 

 of the dissolved particles increases, the importance 

 of the chemical forces probably diminishes, and 

 that of the capillary forces grows. 



If colloid and crystalloid solution are but 

 the extreme limits of a continuous series of 

 phenomena, the study of dissolved colloids of 

 varying degrees of aggregation should throw 

 much light on the general problem of the funda- 

 mental nature of solution. 



A study of the colloidal state is primarily the 

 affair of physics and chemistry. But that study has 

 led to many technical applications, as, for instance, 

 in dyeing, of great industrial importance. More- 

 over, colloids play a supreme part in the phenomena 

 of living matter. Protoplasm, the material basis of 

 life which fills all living cells, is essentially a colloid, 

 and in physiology and biochemistry colloidal 

 problems continually arise. Again, the soil of our 

 fields, so simple to the eyes of the pioneers in 

 agricultural chemistry, is now known to be a 

 complex containing many colloids, with a flora 

 and fauna of its own. But this Is not the place 

 to follow further these fascinating developments — 

 the physics of colloids contains enough of interest. 



