200 FARMYARD MANURE [CHAP. 



the dung-making process under the best conditions. 

 Not only does the loss fall upon the active compounds 

 of nitrogen, but a still further amount is converted 

 into more slowly acting bodies. For example, 

 in experiment i there were 43-83 lb. of digestible 

 nitrogen fed, of which the animal only retained 3-07 ; 

 the remainder, 40-76 lb., was excreted as urea, but only 

 28-6 lb. of ammoniacal and amide nitrogen were found 

 in the dung, so that besides the loss of 7-38 lb. another 

 4-78 lb. had been transformed into proteins and other 

 insoluble compounds. 



It will be seen that in all cases the losses fall most 

 heavily on the rich dung made by animals receiving 

 concentrated foods ; they also fall almost entirely on 

 the most valuable part of the manure — the urea and 

 ammonia compounds arising from the digestible por- 

 tions of the food. It is also clear that these losses are 

 avoided when the food is consumed upon the land, as 

 by sheep folded on the arable, milch cows grazing or 

 beasts fattened with cake upon the summer grass. 



Of course, in all these considerations no account has 

 been taken of such preventable losses as those which 

 too often occur through the escape of the liquid portions 

 of the manure in a leaky yard or into the drains, 

 or by the washing of rain through the dung heap. Such 

 losses are very great and fall on the most valuable 

 substances in the manure — the soluble ammonia and 

 potash compounds which occur in the liquid portion. 



In order to minimise these losses of nitrogen, a 

 number of substances have been suggested, which, when 

 strewn about the cattle stalls and mixed with the fresh 

 dung, would either combine with the ammonia and 

 prevent its volatilisation, or by reducing the bacterial 

 actions would hinder its formation. These preserva- 

 tives fall into two classes : those designed merely to 



