4 CHEMICAL FERTILIZERS 



through, the finest filter, and showing no signs of heterogeneity 

 when observed under a microscope. Some substances of a 

 less constant chemical composition, and of a colloidal nature, 

 only dissolve in water in such a manner that they wholly 

 or partially refuse to pass through the finest filter, and exhibit 

 in the side illumination of an ultra-microscope the appear- 

 ance of a large number of minute particles in rapid motion. 

 These different kinds of solution behave in a very differ- 

 ent manner in passing through the fine walls and minute 

 vessels of a plant. 



Hydrolysis is an important function of water and results 

 in very great changes in chemical composition. As examples, 

 one may give the inversion of cane sugar into glucose and 

 fructose, the conversion of proteins into ammo acids, and the 

 separation of fats into fatty acids and glycerine. In plant 

 life this hydrolysis is usually effected by enzymes. The 

 reverse of hydrolysis is dehydration, an example of which 

 is the conversion of sugar into cellulose. Enzymes are very 

 active chemical agents produced by vital processes ; their 

 action is by no means exclusively limited to hydrolysis, but 

 includes dehydration, oxidation and reduction. It is found 

 by experiment that in a large number of cases the enzyme 

 itself slowly disappears in the course of its activity, although 

 the amount of substance that can be acted upon by an enzyme 

 is very large in proportion to the amount of the enzyme 

 itself. Some preparations of diastase have been prepared 

 of such a strength that they can dissolve 1000 times their 

 own weight of starch. Enzymes, therefore, behave as cata- 

 lysts, and follow many of the general rules of catalysis. 

 The rate of catalytic change is always in proportion to the 

 concentration of the catalyst, but not always in linear propor- 

 tion, because some of the catalyst is destroyed. The 

 gradual destruction of the enzyme leads to a retardation of 

 reaction greater than that due to the diminished concen- 

 tration of the substance undergoing chemical change. Hence 

 the rate of decomposition, when due to an enzyme, generally 

 falls off more rapidly than the logarithmic curve that could 

 be drawn to fit the progress of pure catalysis. 



