FERTILIZERS. 251 



six pounds were applied, at a cost of 5^. per acre, the net gain of which was £1 7 6. This 

 salt, however, is allied to the nitrates, in its effects ; that is, it promotes the growth of stalk. 

 It is however true, that, like the sulphate of lime, its acid may furnish sulphur to the grain of 

 the cereals. This salt is not so expensive as to forbid its use in agriculture ; and being easily 

 transported, may be employed as a fertilizer, upon meadows too distant to admit of carting the 

 bulky and heavy manures. This substance, however, will operate in a manner snnilar to gyp- 

 sum ; it will apparently stimulate the plant to take up more nourishment, and hence a field will 

 be exhausted sooner by its application. 



Phosphate of Magnesia. It is a substance important to all the cereals. It exists in the soil, 

 and, like phosphate of lime, is derived from primary rocks. Not only are the grains composed 

 in part of this salt, but it also forms a constituent part of beets, carrots, parsnips, etc. It exists 

 in the largest quantity in wheat ; and horses which are fed constantly on middlings or 

 shorts, are in danger of accumulations of it in the intestines, in the form of balls. Bones con- 

 tain a small amount of this salt. There is no mineral substance which is composed principally 

 of phosphate of magnesia ; and it is probable that it is formed in plants by a combination of its 

 elements. This fact, however, does not diminish the importance of this phosphate in the econo- 

 my of vegetables. It also exists in manures, especially those derived from animals fed on the 

 grains. 



Mitrate of Magnesia. The nitrate of magnesia is an artificial production, and is prepared 

 in the laboratory, by the union of nitric acid with carbonate of magnesia. Few, if any, ex- 

 periments upon vegetation have been made with this salt. Its action may be supposed favora- 

 ble, considering the importance of both magnesia and nitrogen to plants : it will probably re- 

 semble, in its action the other nitrates. It will usually be formed in the course of the decom- 

 positions which take place in the compost heap. 



3. Potash and its Salts. 



Potash is sometimes called the vegetable alkali, from the fact that the great supply is drawn 

 from the vegetable kingdom. It exists, however, in the mineral kingdom, and is a common 

 constituent of many minerals and rocks. Felspar and granite contain potash, in small quanti- 

 ties, and yet in sufficient abundance to dispose them to crumble, and finally to undergo de- 

 composition, and form a peculiar and valuable porcelain clay. All rocks, if they contained a 

 considerable quantity of potash, would also undergo a rapid decomposition in an atmosphere 

 constituted like ours, where rains and frosts occur in their respective seasons : it would be 

 impossible to protect stone buildings, and prevent a premature decay. Potash may be regarded 

 as one of the most expensive elements of plants. In this respect, it ranks next to idiosphoric 

 acid. Potash, in addition to its value and importance to growing plants, is extensively used 

 in the arts of life, and is, in fact, an indispensable material to civilized nations. In these 

 numerous uses, it is more important than phosphorus, though, in the progress of nations, every 

 element increases in value. Many articles which are not of prime necessity become highly 

 important from convenience : thus the phosphoric matches are almost indispensable in the 



