32 AGRICULTURE. [en. 



58. The rapidity of fermentation is regulated by 

 the admission of air to the heap of manure. If it be 

 desired to make farm-yard manure ferment more 

 quickly, it is turned over so as to lie lightly; but 

 if fermentation has to be checked, it is trodden down 

 into a compact mass. The greater the rapidity of 

 the fermentation may be, the greater is the danger of 

 its throwing off its ammonia into the air, and this 

 renders it the more necessary in such cases to keep 

 it moderately moistened, so that, although it may be 

 a quick fermentation, it may still be kept of a right 

 and proper character. A properly controlled fer- 

 mentation will preserve the ammonia; but if it be 

 neglected, the most valuable constituent of the manure 

 will be thrown into the air. 



CHAPTER V. 

 ARTIFICIAL MANURES. 



59. The term artificial manure is one of recent 

 adoption and is confined almost entirely to fertilizers 

 which have been brought into use within the last forty 

 years. Some of these are natural products, as guano 

 and nitrate of soda ; others are manufactured, as super- 

 phosphate of lime and sulphate of ammonia. This 

 term is not applied to such manures as lime, chalk, 

 marl, and others of ancient use : these may be con- 

 veniently termed natural manures. Thus beside the 

 farm manures we shall have two classes, viz., the 

 artificial and the natural manures. 



60. The first step towards the introduction of 

 artificial manures was the use of bones. These 

 were broken so as to pass through a sieve having 

 a mesh of half an inch. They were and still are 

 known as " half-inch bone." The use of these bones 

 upon dairy pastures had a surprising effect, and they 



