THE USE OF MANURES. 69 



but its escape can easily be determined by the com- 

 mon test for this substance, that is, the formation of 

 a white vapor with hydrochloric acid. A glass rod 

 dipped into this acid, and brought in contact with 

 the gaseous ammonia, will show the effect mentioned. 

 To prevent the escape of ammonia, the heap as it 

 accumulates should be covered or mixed with earth, 

 or sprinkled occasionally with dilute hydrochloric, 

 or sulphuric acid, or solution of ferrous sulphate, 

 known as copperas. Lime and ashes must not be 

 added, because they would release the ammonia, in- 

 stead of retaining it. 



155. Manure-heaps should be kept moist in order 

 that fermentation or decomposition may go on, but 

 should not be exposed to violent rains which wash 

 out soluble ingredients of great value. Perhaps the 

 best and most economical plan for general use, is to 

 pile the manure carefully in rail pens and cover 

 lightly with boards, and, even if not covered, the 

 pens will prevent the scattering and wasting of the 

 manure. The excrements of all our domestic ani- 

 mals should be added to these piles, together with 

 the sweepings of yards, and refuse of all kinds. By 

 this means, with a little attention and no outlay of 

 money, much valuable material which is now lost 

 could be restored to the soil. 



156. Human excrements, so abundant in large 

 cities, form a manure of considerable value. When 

 dried, powdered, and mixed with charcoal, gypsum, 

 etc., it is sold under the name of poudrette. Large 



