MANURES AND THEIR APPLICATION. 



309 



Here again we see from a comparison of the first two columns 

 how great is the advantage derived from merely covering the 

 manure. The increased proportion of organic matter and 

 nitrogen in the other three columns shows that all the substances 

 added had the effect of preserving the manure. The amount 

 of charcoal added v^^as about one quarter per cent., of gypsum a 

 little more, and of lime about a half per cent. Gypsum is seen 

 to have a very marked effect in preserving the manure, and there 

 are many other experiments that might be noticed confirming 

 the very beneficial action of this substance as a fixer of the 

 valuable ingredients of a manure heap; but what is most remark- 

 able in this experiment is the unexpected result, that the best 

 preservative is a small dose of lime. The amount of lime thus 

 added must be very small, not more than one ton to two hundred 

 of manure, and it must be added when the manure is fresh, and 

 layered into the heap during its manufacture. To add lime to a 

 rotten manure heap would cause a great loss of ammonia from 

 the decomposition of the ammonia salts which have been formed 

 during the rotting of the heap, but in fresh dung there are no am- 

 monia salts, and thus the addition of lime occasions no loss, but, 

 on the contrary, preserves the nitrogen of the manure. The rot- 

 ting of the heap goes on, but not quite so rapidly as if no lime had 

 been applied. In the ordinary rotting of a manure heap, a large 

 amount of carbonate of ammonia is formed, and it is that which 

 smells so pungently when a heap is being turned over, but in 

 this case ammonia salts are not found in the heap ; the nitrogen 

 is converted largely into nitric acid, and this is found in com- 

 bination with the lime. This formation of nitric acid is no doubt 

 due to the busy work of the germs I have already alluded to as 

 occurring in fertile soil, and we thus see that by this method of 

 treating manure, the changes which go on in the soil have been 

 anticipated in the manure heap. There is much yet to be learned 

 regarding the preservation of manure, but until we abandon the 

 wasteful method of exposure at present in use nothing that we 

 can learn can be of much use. 



Among tlie mineral substances applied to the soil, lime is the 



