138 STALL-MANURE AND STRAW. 



and depriving it of its volatility ; but it acts only in 

 this way when a large amount of moisture is simul- 

 taneously present. The inefficaciousness, so fre- 

 quently remarked, of strewing gypsum in sheep-pens, 

 is hence explained at once ; the quantity of water 

 essential to its action is wanting. 



Sulphuric acid and green vitriol will be here most 

 advisable and convenient, because they can now be 

 everywhere obtained, and at moderate cost ; oc- 

 casion no expense in their transportation to and 

 fro, like the earths above mentioned ; and are far 

 more energetic in their operation than gypsum. A 

 few pounds of sulphuric acid mixed in water or 

 drainings, and poured upon the dung-heap, will, in a 

 few moments, firmly combine with and fix all free 

 ammonia, and be paid for two or three times over 

 by the ammonia which is thus preserved. Since, 

 moreover, this acid alone is not without manur- 

 ing value, the gain accruing from its use is pro- 

 portionally enhanced. Green vitriol (copperas), be- 

 ing composed of sulphuric acid and iron, and dis- 

 solving readily in water, acts just as quickly as the 

 free sulphuric acid ; and in one respect, indeed, still 

 more completely, in so far as iron possesses the ca- 

 pacity of decomposing and depriving of odor the 

 sulphuretted gas (sulphuretted hydrogen), which is 

 equally generated in the putrefaction of manure, 

 and occasions the disagreeable stench of rotten eggs. 



In Switzerland this salt has long been generally 

 employed for the preservation of drainings, and more 



