202 FARMYARD MANURE [chap. 



carbonates and fix the ammonia as chloride or sulphate. 

 Here, again, the quantity required is very large, though 

 the soluble nature of the kainit enables it to be utilised 

 more thoroughly. But of this class of substances the 

 most effective is superphosphate; the acid calcium 

 phosphate it contains reacts with the ammonium car- 

 bonate to form a double ammonium calcium salt, 

 insoluble indeed, but readily becoming available for 

 the plant. The same objections, however, apply to 

 superphosphate as to gypsum ; uneconomical cjuantitics 

 are required if the fixation of the ammonia is to be 

 complete, the superphosphate itself contains gypsum 

 which becomes reduced to the injurious calcium sul- 

 phide, and again the acid superphosphate is found to 

 be harmful to the feet of the animals treading down 

 the litter among which it is strewn. 



Sulphuric acid itself has been tried, as also peat 

 moss impregnated with small quantities of the same 

 acid, but neither have proved successful for the reasons 

 indicated above. 



As to antiseptics proper, soluble fluorides and even 

 carbon bi-sulphide have been tried, but the saving 

 effected in the nitrogen is never sufficient to pay for 

 the cost of the material and the trouble of applying 

 it. Schneidewind, in the course of his experiments at 

 Leuchstadt, found that the only practical means of 

 reducing the losses of nitrogen, was to place a layer 

 of old well-rotted farmyard manure as a basis for the 

 new manure heap; this had a distinctly beneficial effect 

 and always resulted in smaller losses of nitrogen, 

 probably because of the constant evolution of carbonic 

 acid from the layer of old manure. 



Turning now to the composition of farmyard manure, 

 the average of a large number of analyses at Rotham- 

 sted shows that it contains about three-quarters of its 



