E. J. Russell and E. H. Richards 



551 



The analytical difficulties are considerable, and as the digestibilities 

 are only assumed and not determined, one must not lay too much stress 

 on small difEerences. 



We have made experiments in the laboratory by passing a current 

 of air through the mixture of straw, faeces, and urine for a period of 

 four weeks. Prior to the experiment the urine had undergone a certain 

 amount of fermentation whereby most of its nitrogen had been converted 

 into ammonia. After this experiment the ammonia in the whole mass 

 was determined : in no case was it equal to the amount present at the 

 beginning, showing that a considerable amount had been converted 

 into more complex nitrogen compounds. The results are given in 

 Table VI. 



Table VI. Change of ammoniacal nitrogen into ^' other'' forms of 

 nitrogen during the fermentation of urine, faeces, and straw under 

 aerobic conditions. 



But when we came to deal with masses of farmyard manure, whether 

 we used only the 10 lbs. quantities taken for the laboratory experiments, 

 or the one or two ton heaps used for outdoor experiments, we were 

 unable to find evidence of such a change. In some 20 different 

 experiments only one showed any sign of gain in complex nitrogen 

 compounds, and there the increase was only 8 % on the quantity 

 measured, which in turn was a difference involving three separate 

 measurements. 



Only when the heap is composed entirely of horse manure do we get 

 any increase in the complex nitrogen compounds. The^ results are 

 given in Table VII 1. 



1 For further experiments with horse manure see this Journal, 1917, 8. 299. 



