Catalogue of Works on Gardening, Sj-c. 373 



ing at the present time, when so much has been recently said respecting them 

 by Liebig, Dr. Daubeny, and others. 



" Ammonia. — If the sal-ammoniac of the shops be mixed with quicklime, a 

 powerful odour is immediately perceived, and an invisible gas is given off, 

 which strongly affects the eyes. This gas is ammonia. Water dissolves or 

 absorbs it in very large quantity, and this solution forms the common harts- 

 horn of the shops. The white solid smelling-salts of the shops are a com- 

 pound of ammonia with carbonic acid, — a solid formed by the union of two 

 gases. 



" The gaseous ammonia consists of nitrogen and hydrogen only, in the 

 proportion of 14; of the former to 3 of the latter, or 17 lb. of ammonia contain 

 3 lb. of hydrogen. 



" The chief natural source of this compound is, in the decay of animal sub- 

 stances. During the putrefaction of dead animal bodies ammonia is in- 

 variably given off. From the animal substances of the farm-yard it is evolved, 

 and from all solid and liquid manures of animal origin. It is also formed in 

 lesser quantity during the decay of vegetable substances in the soil ; and in 

 volcanic countries, it escapes from many of the hot lavas, and from the 

 crevices in the heated rocks. 



" It is produced artificially by the distillation of animal substances (hoofs, 

 horns, &c), or of coal. Thousands of tons of the ammonia present in the 

 ammoniacal liquors of the gas-works, which might be beneficially applied as a 

 manure, are annually carried down by the rivers, and lost in the sea. 



" The ammonia which is given off during the putrefaction of animal sub- 

 stances rises partially into the air, and floats in the atmosphere, till it is either 

 decomposed by natural causes, or is washed down by the rains. In our 

 climate, cultivated plants derive a considerable portion of their nilrogen from 

 ammonia. It is supposed to be one of the most valuable fertilising sub- 

 stances contained in farm-yard manure; and as it is present in greater 

 proportion by far in the liquid than in the solid contents of the farm-yard* 

 there can be no doubt that much real wealth is lost, and the means of raising 

 increased crops thrown away, in the quantities of liquid manure which are 

 almost every where permitted to run to waste. 



" Nitric Acid is a powerfully corrosive liquid, known in the shops by the 

 familiar name of aquafortis. It is prepared by pouring oil of vitriol (sulphuric 

 acid) upon saltpetre, and distilling the mixture. The aquafortis of the shops 

 is a mixture of the pure acid with water. 



" Pure nitric acid consists of nitrogen and oxygen only ; the union of these 

 two gases, so harmless in the air, producing the burning and corrosive com- 

 pound which this is known to be. 



" It never reaches the roots of plants in this free and corrosive state. It 

 exists in many soils, and is naturally formed in compost heaps, and in most 

 situations where vegetable matter is undergoing decay in contact with the air ; 

 but it is always in a state of chemical combination in these cases. With 

 potash, it forms nitrate of potash (saltpetre), with soda, nitrate of soda, and 

 with lime, nitrate of lime; and it is generally in one or other of these states of 

 combination that it reaches the roots of plants. 



" Nitric acid is also naturally formed, and in some countries probably 

 in large quantities, by the passage of electricity through the atmosphere. The 

 air, as has been already stated, contains much oxygen and nitrogen mixed 

 together ; but when an electric spark is passed through a quantity of air, 

 a certain quantity of the two unite together chemically, so that every spark 

 that passes forms a small portion of nitric acid. A flash of lightning is only 

 a large electric spark ; and hence every flash that crosses the air produces 

 along its path a quantity of this acid. Where thunder-storms are frequent, 

 much nitric acid must be produced in this way in the air. It is washed down 

 by the rains, in which it has frequently been detected, and thus reaches the 

 soil, where it produces one or other of the nitrates above mentioned. 



" It has been long observed that those parts of India are the most fertile 



B B 3 



