ACTION' OF SALTS. 125 



160. The second class of salts belonging to the first divi- 

 sion, or nourishers (6. 158), are the nitrates, including not 

 only saltpetre, both East Indian and South American, or 

 nitrate of potash and nitrate of soda, but also all composts 

 of lime, alkali, and animal matter. The last produces am- 

 monia, which, without the alkali, would act on geine and 

 render that soluble. Ammonia, by the mere act of presence, 

 hastens decay ; but without the influence of lime, or alkali, 

 ammonia is changed to nitrate of ammonia (126), for this 

 base, by the oxygen of the air, is changed into aquafortis, or 

 nitric acid. While a portion of acid and base are present, 

 they unite and form a salt. A portion of ammonia is thus 

 continually withdrawn. If lime or alkali is present, the 

 nitric acid unites with these, leaving the ammonia to act on 

 geine. 



167. Thus, in a compost of animal matter without alkaline 

 bases, all the geine has not been rendered soluble, as is 

 usually supposed, by the action of ammonia. Before the 

 full action of that element has been exerted on the organic 

 matter, it has been converted into a nitrate. But if the 

 lime exceeds that which the nitric acid can saturate, then the 

 soluble geine is seized upon and becomes inert. Nitrates 

 act under the influence of the growing plant ; the base let 

 loose, acts on geine ; the acid is decomposed, and its nitro- 

 gen given up to the plant, becomes one of their essential ele- 

 ments. The elements of nitrate of ammonia are all taken 

 up, both acid and base. If there are any salts which can be 

 called vegetable food, they are the nitrates. The organic 

 constituents of plants are hydrogen and oxygen, carbon and 

 nitrogen. By their union, the two first form water ; the two 

 middle carbonic acid ; the first and last ammonia. Water, 

 ammonia, and carbonic acid, then, or their elements, com- 

 pose the organic part of all plants. Water and carbon exist 



