VAEIOUS KINDS OF MANURE. 139 



alkalies, but also on account of the nitrogen which they contain, in the 

 form of nitric acid. The quantity of glutin is said to be increased by 

 the use of nitrates. Carbonate of potash and soda, and chloride of 

 sodium, are frequently used as manures. The latter is especially use- 

 ful in the case of plants cultivated inland, which were originally 

 natives of the sea-shore, as Cabbage, Asparagus, and Searkale. As 

 lime is found in all plants, the salts containing it are of great import- 

 ance. It may be used in the caustic state with the view of decom- 

 posing vegetable matter. It also neutralises any acids previously in 

 the soil, such as occur occasionally in boggy and marshy land, abound- 

 ing in species of Juncus, Carex, and Eriophorum, with some Calluna 

 vulgaris. Lime also combines with certain elements of the soil, and 

 sets potash free, which reacts on the silica, and renders it soluble. 

 Lime is sometimes washed down into the subsoil ; and in such cases 

 trenching improves the land. Phosphate of lime is a valuable manure, 

 both on account of the lime, and of the phosphorus which it contains. 

 Without the presence of phosphates, glutin and the protein compounds 

 of plants cannot be formed. Phosphate of lime exists abundantly in 

 animal tissues, and hence it must be furnished by plants. The iise 

 of bone-dust as a manure depends in a great measure on the phos- 

 phate of lime which it contains. Besides phosphate of lime, bone-ash 

 contains from 3 to 12 per cent of phosphate of magnesia, carbonate 

 of lime, and salts of soda. The gelatine of bones also seems to act 

 beneficially, by forming carbonic acid and ammonia. Bones are best 

 applied after being acted on by sulphuric acid, so as to form soluble 

 phosphates by decomposition. They are broken into pieces, and 

 mixed with half their weight of boiling water, and then with half 

 their weight of sulphuric acid. The superphosphate thus formed is 

 applied to the soil, either in a dry state by the drill, with sawdust 

 .and charcoal added, or in a liquid state, diluted with 100 to 200 parts 

 of water. Phosphates and other inorganic matters .sometimes exist 

 potentially in the soil, but in a dormant state, requiring the addition 

 of something to render them soluble. Allowing the ground to lie 

 fallow, stirring and pulverising it, are methods by which air and 

 moisture are admitted, time being allowed for the decomposition of 

 the materials, which are thus rendered available for plants. Sulphur 

 exists in considerable quantity in some plants, as Oruciferse, and it 

 forms an element in albumin ; hence the use of sulphuric acid and of 

 sulphates as manures. Sulphate of lime or gjrpsum is well fitted as 

 a manure for clover, by supplying sulphur and lime, and absorbing 

 ammonia. Charcoal in a solid state has been applied with advan- 

 tage as a manure. It acts partly by taking up ammonia in large 

 quantity, and partly by combining slowly with oxygen, so as to form 

 carbonic acid. The effects of carbonic acid on vegetation are said to 

 be remarkably conspicuous in some volcanic countries, in which this 



