TEE AOBICULTURAL JOURNAL. (',49 



Agricultural Chemistry for Beginners. 



CHAPTER III. 

 By Archibald Pearcb. 

 NITROGEN AND AMMONIA. 



NITROGEN is an elemeat of the highest 

 agricultural importance. It is another 

 gas, of which four-fifths of the air by 

 measure consist. By nature it is exceed- 

 ingly inactive, and does not readily com- 

 bine with other elements, and this is the 

 reason why, although so abundant in the 

 atmosphere, various nitrogenous manures 

 have often to be applied to the soil ; for 

 all plants must have nitrogen for their 

 growth, and only a few have the power 

 of obtaining it from the air. In the air 

 it acts as a check on the active and 

 vigorous oxygen, diluting it, as it were, 

 and preventing the too violent actions 

 that would otherwise take place. The 

 nitrogen that plants need is never ab- 

 sorbed into their tissues in its elementary 

 form, but always in the shape of its com- 

 pounds ; accordingly nothing further will 

 be said about it, but we shall proceed at 

 once to its compounds, of which the chief 

 are Ammonia and Nitric acid. 



Ammonia and Alkalies. 



Ammonia introduces us to a class of 

 compounds called alkalies, which are 

 exactly opposite in their qualities to acids. 

 They have a kind of soapy taste, and if 

 applied to litmus paper that has been red- 

 dened by an acid they restore its blue 

 colour again. Litmus paper is thus very 

 useful as a test ; an acid substance reddens 

 it, an alkaline substance turns the colour 

 back to blue, and if no effect is produced 

 on either the red or blue paper the sub- 

 stance is said to be neutral. The alkalies 

 act as bases, inasmuch as if mixed with 

 acids they produce salts. The best known, 

 besides ammonia, are caustic potash, 

 caustic soda, and the alkaline earth lime. 



Ammonia is a compound of nitrogen 

 and hydrogen, in the proportion of 14 

 parts bj weight of nitrogen to 3 of hydro- 

 gen. It is in reality a gas, but is very 

 soluble in water, and this solution is the 

 liquid commonly sold as ammonia. It is 



in almost all cases the product of the de 

 composition of animal or vegetable sub- 

 stances containing nitrogen. If a tuft of 

 hair, or a few feathers, or a piece of horn 

 be heated in a thin closed glass tube over 

 a flame, we shall observe a few drops of 

 a more or less evil-smelling liquid pro- 

 duced, and if we test this with red litmus 

 paper, the presence of ammonia will be 

 shown by the change of colour to blue. 

 If a rotting manure-heap is allowed to get 

 too dry, we can often smell the escaping 

 ammonia, or show its presence by laying 

 a piece of red litmus paper on the top, 

 proving that the valuable nitrogen is 

 being wasted. Any chemist will supply 

 a little red or blue litmus paper for a few 

 pence. The chief commercial source of 

 ammonia is the gas-works, where illumi- 

 nating gas is distilled from coal, which 

 contains a small proportion of nitrogen ; 

 the ammonia is dissolved by the water in 

 which the gas is washed, and the various 

 ammonia products are manufactured from 

 the solution. 



Ammonia is generally believed not to 

 be easily, if at all, assimilated as such by 

 growing plants ; it must first be converted 

 into nitrates, as will be described in the 

 next chapter. Most soils have the power 

 of absorbing and holding ammonia, and 

 not allowing it to be easily washed away, 

 a property that is often of importance in 

 a country subject to heavy downpours of 

 rain. 



Ammonia very readily combines with 

 acids, acting as a base, and forming salts 

 of ammonia, generally called ammonium 

 salts. The best known of these are sul- 

 phate of ammonia (ammonium sulphate) 

 and sal-ammoniac (ammonium chloride). 

 The ammonia in all ammonium salts is 

 easily expelled by the action of lime ; one 

 can illustrate this important fact by mix- 

 ing a small quantity of sal-ammoniac or 

 sulphate of ammonia with a similar 

 quantity of lime, when the ammonia 



