CHEMICAL MANU11KS. 29 



Thus the azotic matter produces a little more effect than all the 

 ten minerals together, but the harvest does not take the character of 

 n high culture until the two orders of compounds are united. 



We may add, that when we pass from burnt sand to the natural 

 soil the number of minerals employed as fertilizers may be reduced 

 from ten to three. If, under these new conditions, we make two par- 

 allel experiments, one with azotic matter and the ten minerals that 

 you already know, and the other with azotic matter and but three 

 minerals phosphate of lime, potash and lime the returns will bo 

 equal. 



In the burnt aud this suppression renders vegetation impossible ; 

 now, as it does not suffer from it in the natural earth, it is evident 

 that these seven minerals exist in the soil. The most favorable con- 

 ditions to fertility are found realized in the union of these three 

 terms azotic matter, phosphate of lime and lime. It is for this 

 reason I have given this mixture the name of a complete fertilizer. 



Finally, to assure you of what I have said, permit me to place 

 before you a ' series of harvests obtained from good earth enriched 

 with chemical manures alone. The great inequalities which they 

 show are caused solely by the suppression of one of the four terms 

 of the complete fertilizer, showing how indispensable is the union of 

 these four to a flourishing vegetation. 



Although these ten elements which we have just discussed aid in 

 the production of vegetation, yet to fulfill their duties they imperi- 

 ously demand the aid of another order of materials, also contained in 

 the soil, and of which I must now speak. These materials, three in 

 number viz., clay, sand and humus differ from the preceding by 

 the pure passiveness of their functions. They serve to support plants, 

 but do not of themselves maintain vegetable life. To distinguish 

 them from the first, which have received the name of the " assimilable 

 elements" of the soil, we call them the "mechanical elements" 



But this is not all; the "assimilable elements" are themselves 

 divided into two groups. The active assimilable elements are the 

 assimilable elements in reserve, so called because they cannot aid in 

 vegetable production but after being submitted to decomposition, 

 which allows plants to absorb them. 



I will give you an example to show the necessity of this distinc- 

 tion. 



Azotic matters of animal origin produce ammonia and the nitrates 

 in its decomposition, and owe their useful effects to this formation ; 

 the skin and offal of animals come particularly under this head, 

 because they are decomposed with uneqUaled facility and quickness. 

 But if these skins have been tanned, if they have become leather, 

 they decompose slowly and lose a part of their immediate activity. 



In the first place, they belong to the group of active assimilable 

 elements, while in the second case they enter the group of 'assimilable 

 elements in reserve. 



Well, there are mineral and organic properties in the soil which 

 only exert a useful action after submitting to a preyious decompo- 

 sition more or lees slow. 



