12 Farmyard Manure. 



In fermenting horse-rdung, the proportion of nitrogen is thus larger 

 than in fresh, which agrees well with previous analyses of fresh 

 or rotten common yard-manure ; whilst in perfectly fresh horse- 

 dung the amount of free ammonia is scarcely weighable, it being 

 only about 3 parts in every 100,000 parts of dung, or 3 Ibs. for 

 every 40 tons ; the same description of manure in an active state 

 of fermentation yields somewhat more, but still a very incon- 

 siderable quantity of free ammonia. Thus under the most 

 favourable circumstances 100,000 parts of horse-dung yield only 

 49 parts of free ammonia ; or in other words 40 tons in round 

 numbers yield on long-continued boiling only 49 Ibs. of ammonia. 

 It must not be supposed, however, that this quantity of ammonia 

 is dissipated into the air during the fermentation of the dung, for 

 it is only in the interior of the dung-heap that ammonia is libe- 

 rated. It is, indeed, only on turning a heap that ammonia 

 escapes at all in any perceptible degree ; but as soon as the ex- 

 ternal layers have become cooled down to the ordinary temperature 

 of the air its escape is arrested. There can, therefore, be not the 

 slightest doubt that a very minute quantity of ammonia passes 

 into the air and the remainder is fixed in the heap, provided 

 the heap is kept in such a manner that rain cannot remove 

 from it much of the soluble matters, and with them ammoniacal 

 salts. 



The strong smell which is observed on turning a dung-heap 

 no doubt has led many greatly to over-estimate the amount of 

 ammonia which escapes from farmyard manure in an active state 

 of fermentation. But I would observe that nothing is more fal- 

 lacious than the estimation of the amount of ammonia by the 

 pungency of the smell which is given off from fermenting animal 

 matters. Such matters often give off a very powerful smell, 

 which is due to peculiar volatile organic combinations to some 

 sulphuretted and phosphoretted hydrogen and a great variety of 

 gaseous matters, amongst which there is ammonia gas in very 

 minute quantities. The smell of this highly complicated and 

 but scantily examined mixture of gaseous matters as a whole is 

 ascribed by the popular mind to ammonia. From these products 

 of putrefaction, however, ammonia can be completely separated, 

 without in the least destroying the peculiar offensive smell which 

 emanates from organic matters in a state of decomposition. If, 

 for instance, dilute sulphuric acid is added to farmyard manure 

 or liquid manure, the smell of these substances, instead of 

 becoming neutralised by the acid, in reality becomes more offen- 

 sive. This arises in a great measure from the liberation of sul- 

 phuretted hydrogen. Hence acids are not well adapted for dis- 

 infecting cesspools or nightsoil. As dilute sulphuric acid 

 neutralises instantly free ammonia, forming with it an inodorous 



