28 PRACTICAL FARM CHEMISTRY. 



acids, and this gives us a clue how to catch and hold 

 it for use just where needed. It is especially fond 

 of sulphuric acid, and whenever the two meet, they 

 at once enter a close (chemical) union, forming the 

 salt " sulphate of ammonia." 



This is the reason, and a good one, why the advice 

 is so often given to scatter sulphate of lime (gyp- 

 sum or plaster), sulphate of iron (green 



^rtchers* copperas), kainit, or other compounds of 

 sulphuric acid, over fermenting manure 

 heaps and in stables. If followed, it will result in 

 saving most of the precious but fleeting gas ammonia, 

 and holding it fast, for use as plant food, in the 

 form of a solid salt, soluble in water, but not vola- 

 tile. The ammonia, formed freely in the soil' when 

 decaying vegetable matter is present, and although 

 so exceedingly volatile when free, has but little 

 opportunity to escape into the air, as 



intiieSMi. *^^ ®^^^ water, and the various , acids 

 (humic, ulmic, etc.,) resulting frofn the 

 interaction of the carbon and oxygen in the soil, are 

 quite apt to fix and hold it there for ready use of 

 plants. Ammonia forms also quite freely in the ex- 

 crements of animals, especially so in urine, and is 

 just the substance that gives to these manures their 

 great value and quick-acting character. 



Nitrogen also combines with oxygen. These two 

 elementary bodies, as already stated, exist in the 

 atmosphere in a mere mixture ; and that it needs 

 considerable compulsion to make them unite chemi- 

 cally, is a fortunate thing for us, for the combination,, 

 nitric acid, is a most powerful, corrosive and de- 

 structive substance, and its free combination in the 

 atmosphere might make things rather uncomfort- 

 able for living creatures. There is still a good deal 



