42 PLANT PRODUCTS 



price of nitrogen is i6s. If super-phosphate, with 30 per 

 cent, of soluble phosphate, cost about £6 per ton, each one 

 per cent, will cost 4s. It will be noted, in comparing the 

 tables of the Journal of the Board of Agriculture, that 

 sometimes special forms are very expensive ; for example, 

 in dissolved bones soluble phosphate is much more expensive 

 than in super-phosphate. The nitrogen in dissolved bones 

 is assessed at a high rate, as it is also in the case of nitrate 

 of soda, but all these conditions are quite temporar}^ and 

 a few months later on the relative prices may be different. 



In practice, the farmer should endeavour to discover 

 for himself, by experiments, what particular mixture suits 

 his soil and system of farming. 



Farmyard Manure. — This very ancient and well- 

 known commodity owes its value partly to its chemical, 

 partly to its physical, and partly to its biological effects. 

 The elementary constituents are carbon, hydrogen, oxygen, 

 and nitrogen, which constitute the non-metallic part ; 

 potassium, phosphorus, calcium, which constitute the metallic 

 part, both parts being of value ; with some small amounts 

 of aluminium, iron, and silicon, which may be considered as 

 having no value. These materials are combined together 

 as humus, organic fibre, and salts. Water is present to the 

 extent of from 60 per cent, to 80 per cent. Farmyard manure 

 is by no means a dead thing. It is full of bacterial life, 

 which has a strong influence on its value. Considering, first 

 of all, the forms in which these elements of value occur, we 

 find that the nitrogen is very rarely indeed in the oxidized 

 condition of a nitrate. Very old heaps of farmyard manure, 

 say two years old, certainly do contain small quantities of 

 nitrate, but this age is not usual in farm practice. An 

 important fraction of the nitrogen is present in the form 

 of ammonia, which chiefly occurs as the result of the 

 decomposition of urea CO(NH2)2. Urea is fermented by 

 a special micro-coccus, so that in a day or so the urea has 

 become completely converted into ammonium carbonate. The 

 ultimate result of this change is represented by the equation 

 CO(NH2)2 + 2H20 = (NH4)2C03. The ammonia so produced 



