256 THE FEEDING EXPERIMENTS 



food. Thus when stock consume linseed cake, Lawes and 

 Gilbert calculated that every 6 lb. of food produced 1 lb. 

 increase in live weight containing 1 "27 per cent, of nitrogen ; so 

 that if 1 ton were consumed, out of the 106*4 lb. of nitrogen in 

 the cake the animals would retain 474 lb., and pass on to the 

 manure 101 '66 lb. The same ton of linseed cake would contain 

 44*8 lb. of phosphoric acid, of which the fattening animal would 

 only retain 3"21 lb., and 31*4 lb. of potash, of which the animal 

 would only retain 0*4 lb. 



When dealing, however, with less concentrated foods the 

 amount required to produce 1 lb. of increase would be much 

 greater and the toll taken by the animal of the nitrogen in the 

 food would also increase. For example, 1 ton of oat straw 

 contains 11*2 lb. of nitrogen, of which the animal would retain 

 1*6 lb. and pass on 9*6 lb. to the manure — only 86 per cent, of 

 that wdiich had been fed instead of over 95 per cent., as in the 

 case of linseed cake. 



From data of this kind Lawes and Gilbert were able to 

 calculate for each of the named foods the amount of nitrogen, 

 phosphoric acid, and potash which would go to the manure. 

 The experiments before mentioned had gone to show that there 

 is no loss of nitrogen during the actual feeding pi'ocess. 

 However, it had been ascertained that even under the best 

 conditions (as in the cattle-feeding experiments at Woburn 

 before alluded to) there were great losses of nitrogen in making 

 the dung before the manm-e reached the land, these losses being 

 due in the main to the volatilisation of ammonia resulting 

 from the rapid fermentation of the urea. Such losses, too, fall 

 upon the urea, the most valuable part of the excreta, since the 

 undigested food residues in the faeces decay so slowly in the 

 ground as to have a lower manm^e value. Very few data 

 •existed from which to determine how large these losses are 

 under ordinary farming conditions, but Lawes and Gilbert felt 

 safe in assuming that at least one-half of the manurial material 

 voided by the animal is lost during the making and storage of 

 the dung, and does not come back to the land in the manure. 



