37 



necessary to sprinkle with water from day to day until such action 

 ceases. This wetting, whether with the leachings or with water, 

 should be done with the most possible regularity. After the manure 

 is placed on the pile, it should not be disturbed, but it should be 

 stamped and packed away from the air. These steps are neces- 

 sary to prevent the loss of potash and phosphoric acid, and espe- 

 cially of nitrogen, both by the formation and evaporation of 

 ammonia and the separation and escape of nitrogen gas itself. 



As the making of barnyard manure is principally a matter of 

 fermentation, special study should be given to this combination 

 of changes. When a pile of manure lies for months without dis- 

 turbance, it grows smaller and smaller. It is comparatively dry, 

 the straw has disappeared and become- " humus." The whole 

 mixture is more uniform in color and character. It is half rotted ; 

 then, after a few more months the bulk has grown very much smaller, 

 and a black, moist, slimy homogenous mass results ; the manure is 

 well rotted. 



Chemists have long known in a general way what changes take place 

 during this process, but not until recently has anything like a sat- 

 isfactory explanation of them been made. This explanation de- 

 pends upon the discovery of existence and actions, in the manure, 

 of three classes of very small microscopic organisms called bacteria. 

 They are responsible, not wholly, but chiefly, for the changes men- 

 tioned. Let us note here just what chemical materials are in the 

 manure at the beginning, and what they are changed into. 



The fresh manure contains mineral substances like potash and 

 phosphates, and also organic material of two kinds, namely : The 

 nitrogenous, found in the liquid manure and to some extent in the 

 solid, and the non-nitrogenous, which largely makes up the straw, 

 leaves, sawdust and solid excrement. It is just these two kinds of 

 organic constituents, and what they become, which concern us now. 



In those portions of the manure which are accessible to the air 

 one class of bacteria live and breed in enormous numbers. They 

 feed on the oxygen of the air and the nitrogenous portions of the 

 manure, and, in their excrements, give off large quantities of 

 nitrates, the latter being the direct products of the oxidation of 

 nitrogenous organic matter anywhere, whether in the bodies of these 

 bacteria or not. These nitrates, being very soluble in water, drain 

 down into the interior of the manure heap, just as they drain 

 through the soil. But instead of all going off in the drainage water 

 and becoming lost, as they often do in the soil, they are chiefly 

 lost by an entirely different process. 



In the interior of the heap, shut away from the air, these nitrates 

 fall prey to another class of bacteria, known as " nitrate de " 



