80 PROPERTIES OF AMMONIA. 



in oxygen gas, the carbon it contains is converted into carbonic acid 

 (COo), and the hydrogen into water (HO). 



Like oxalic acid this gas cannot, by any known process, be produced 

 from the direct union of the carbon and hydrogen of which it consists. 

 It- is readily obtained, however, by heating acetate of potash in a retort, 

 with an equivalent proportion of caustic baryta. [Acetate of potash is 

 ])repared by pouring vinegar (acetic acid) on common pearlash and 

 evaporating the solution.] 



In nature it is largely evolved in coal mines, and is the principal com- 

 bustible ingredient in those explosive atmospheres which so frequently 

 cause disastrous accidents in mining districts. 



This gas is also given off along with carbonic acid during the fermcH- 

 tation of compost heaps, or of other large collections of vegetable mat- 

 ter. It is said also to be generally present in well manured soils, 

 [Persoz, Chimie Moleculaire, p. 547,] and is supposed by many to con- 

 tribute in such cases to the nourishment of plants. It is, however, very 

 sparingly soluble in water, so that in a state of solution, it cannot enter 

 largely into the pores of the roots, even though it be abundantly present 

 in the soil. How far* it can with propriety be regarded as a general 

 source of food to plants, will be considered in the following lecture. 



§ 5. Ammonia, its properties and relations to vegetable life. 



Ammonia is a compound of hydrogen and nitrogen. It is possessed 

 of many interesting properties, and is supposed to perform a very im- 

 portant part in the process of vegetation. It will be proper, therefore, 

 to illustrate its nature and properties with considerable attention. 



Ammonia, like the nitrogen and hydrogen of which it is composed, is 

 a colourless gas, but, unlike its elements, is easily distinguished from 

 all other gaseous substances by its smell and taste. 



It possesses a powerful penetrating odour (familiar to you in the sinell 

 of hartshorn and of common smelling salts), has a burning acrid alka- 

 line* taste, extinguishes a lighted taper as hydrogen and nitrogen do, but 

 does not itself take fire like the former. It instantly suffocates animals, 

 kills living vegetables, and gradually destroys the texture of their parts. 



It is absorbed in large quantities by porous substances, such as char- 

 coal — \^ich, as already stated, absorbs 95 times its own bulk of am- 

 moniacal gas. Porous vegetable substances in a decaying state likewise 

 absorb it. Porous soils also, burned bricks, burned clay, and even com- 

 mon clay and iron ochre, which are mixed together on the surface of 

 most of our fertile lands — all these are capable of absorbing or drinking 

 m, and retaining within their pores, this gaseous substance, when it hap- 

 pens to be brought into contact with them. 



But the quantity absorbed by water is much greater and more sur- 

 prising. If the mouth of a bottle filled with this gas be immersed in 

 water, the latter will rush up and fill the bottle almost instantaneously; 

 and if a sufficient supply of ammonia be y)resent, a given quantit}' of 

 water will take up as much as 670 times its bulk of the gas. 



This solution of ammonia in water is the spirit of hartshorn of the 

 «hops. When saturated [that is, when gas is supplied till the water re- 



• The term alkaline, as applied to taste, will be best understood by describing it as a taste 

 Imilar to that of the common soda and pearlash of the shops. 



