NOURISHMENT OF PLANTS. 39 



of air or gas. Hence, if the process of putrefaction 

 does not take place in the ground, it escapes into the 

 atmosphere. By combination with acids (for in- 

 stance, muriatic acid), or with humus, which com- 

 ports itself in the same manner as an acid, ammonia 

 may be deprived of its volatility. Such combina- 

 tions are called ammoniacal salts. 



Whoever wishes to become more accurately ac- 

 quainted with this gas, so eminently important to 

 vegetable growth (which may be represented to the 

 farmer as '■^putrid nitrogen"), needs only to buy a 

 small quantity of hartshorn, such as may be obtained 

 from the apothecary, to heat it in a plated spoon over 

 the flame of a lamp, and .to hold over it an empty 

 tumbler. The liquid part of hartshorn is water, con- 

 taining a large quantity of ammonia in solution ; up- 

 on being heated, the latter escapes, and mounts into 

 the tumbler. To the external eye the glass seems 

 empty, but the odor which is perceived-" reveals at 

 once that it contains a pungent gas. This odor is 

 entirely identical with that which is noticed, and is 

 often very offensive, in stables, sheep-pens, or water- 

 closets. Here it originates from putrefying animal 

 excrements, and exhales into the air. 



But there is also a second combination of ni- 

 trogen which must be regarded as a means of nour- 

 ishment to plants. This is produced when sub- 

 stances containing nitrogen putrefy in connection 

 with bases (lime, potash, etc.). By the agency of 

 the latter, the nitrogen, instead of uniting with hydro- 



