XII.] LOSS OF WEIGHT IN DUNG-MAKING 229 



anaerobic organisms, which give rise on the one hand 

 to carbon dioxide and marsh-gas or hydrogen, and on 

 the other hand to the dark brown substance of indefinite 

 composition which we call humus. Analysis of the gas 

 derived from a newly made dunghill showed that at 

 first a good deal of hydrogen was being produced, but 

 when the dunghill was kept tight and moist the most 

 characteristic fermentation was that giving rise to 

 carbon dioxide and marsh-gas. Only when the mass 

 was allowed to get dry, so that air could enter, did the 

 aerobic fermentation, giving rise to carbon dioxide 

 alone, begin to take place. It will be seen, however, 

 that a considerable loss of dry material must take place, 

 because whether the fermentation takes place in the 

 presence or absence of air, solid carbohydrates are being 

 converted into gases like carbon dioxide and marsh-gas. 

 We find, as a matter of fact, that during the making of 

 dung, something like a quarter of the original dry matter 

 is burnt up, and that by the time the dung has been 

 made and stored, this loss of dry matter has been 

 increased to one-half, and may easily become greater 

 with very old short manure. 



Turning now to the nitrogenous compounds which 

 form the chief fertilising elements of the manure, we 

 have already said that the most important is the soluble 

 urea contained in the urine. This substance is at once 

 attacked by bacteria which are always present in cattle 

 stalls, stables, etc., and by a very slight chemical change 

 is converted into carbonate of ammonia. Carbonate of 

 ammonia is a substance which spontaneously splits up 

 into the two gases carbon dioxide and ammonia, so that 

 when any liquid containing carbonate of ammonia is 

 exposed to the air and dried up at all, the valuable 

 ammonia is at once converted into gas, and escapes. In 

 this way a great loss of fertilising material can easily 



