S48 SCIENCE OF AGRICULTURE. Part II. 



of each. It is a compound insoluble in pure water, but soluble in water containing any 

 acid matter. It forms the greatest part of calcined bones. It exists in most excremen- 

 titious substances, and is found both in the straw and grain of wheat, barley, oats, and 

 rye, and likewise in beans, peas, and tares. It exists in some places in these islands 

 native, but only in very small quantities. Phosphate of lime is generally conveyed to the 

 land in the composition of other manure, and it is probably necessary to corn crops and 

 other white crops. 



2303. Bone-ashes calcined and ground to powder will probably be found useful 

 on arable lands containing much vegetable matter, and may perhaps enable soft peats to 

 produce wheat ; but the powdered bone in an uncalcined state is much to be preferred in 

 all cases when it can be procured. 



2304. The saline compounds of magnesia will require very little discussion with regard 

 to their uses as manures. In combination with sulphuric acid, magnesia forms a soluble 

 salt. This substance, it is stated by some enquirers, has been found of use as a manure ; 

 but it is not found in nature in sufficient abundance, nor is it capable of being 

 made by art sufficiently cheap to be of useful application in the common course of 

 husbandry. 



2305. Wood-ashes consist principally of the vegetable alkali united to carbonic acid j 

 and as this alkali is found in almost all plants, it is not difficult to conceive that it may 

 form an essential part of their organs. The general tendency of the alkalies is to give 

 solubility to vegetable matters ; and in this way they may render carbonaceous and other 

 substances capable of being taken up by the tubes in the radical fibres of plants. Vege- 

 table alkali likewise has a strong attraction for water, and even in small quantities 

 may tend to give a due degree of moisture to the soil, or to other manures ; though this 

 operation, from the small quantities used or existing in the soil, can be only of a 

 secondary kind. 



2306. The mineral alkali or soda is found in the ashes of sea- weed, and may be pro- 

 cured by certain chemical agencies from common salt. Common salt consists of the 

 metal named sodium, combined vnth chlorine ; and pure soda consists of the same metal 

 united to oxygen. When water is present, which can afford oxygen to the sodium, soda 

 may be obtained in several modes from salt. The same reasoning will apply to the 

 operation of the pure mineral alkali, or the carbonated alkali, as to that of the vegetable 

 alkali ; and when common salt acts as a manure, it is probably by entering into the 

 composition of the plant in the same manner as gypsum, phosphate of lime, and the 

 alkalies. Sir John Pringle has stated, that salt in small quantities assists the decomposi- 

 tion of animal and vegetable matter. This circumstance may render it useful in certain 

 soils. Common salt, likewise, is offi^nsive to insects. In small quantities it is sometimes 

 a useful manure, and it is probable that its efficacy depends upon many combined causes. 

 Some persons have argued against the employment of salt ; because, when used in 

 large quantities, it either does no good, or renders the ground sterile ; but this is a 

 very unfair mode of reasoning. That salt in large quantities rendered land barren, 

 was known long before any records of agricultural science existed. We read in the 

 Scriptures, that Abimelech took the city of Shechem, " and beat down the city, and sowed 

 it with salt ;" that the soil might be for ever unfruitful. Virgil reprobates a salt 

 soil ; and Pliny, though he recommends giving salt to cattle, yet affirms, that when 

 strewed over land it renders it barren. But these are not arguments against a proper 

 application of it. Refuse salt in Cornwall, which, however, likewise contains some of 

 the oil and exuviae of fish, has long been known as an admirable manure ; and the 

 Cheshire farmers contend for the benefit of the peculiar produce of their county. It is 

 not unlikely, that the same causes as those which act in modifying the operation of gyp- 

 sum influence the effects of salt. Most lands in th's island, particularly those near the 

 sea, probably contain a sufficient quantity of salt for all the purposes of vegetation ; and 

 in such cases the supply of it to the soil will not only be useless, but may be injurious. 

 In great storms the spray of the sea has been carried more than fifty miles from 

 the shore ; so that from this source salt must be often supplied to the soil. Salt is 

 found in almost all sandstone rocks, and it must exist in the soil derived from these rocks. 

 It is a constituent likewise of almost every kind of animal and vegetable manure. A va- 

 riety of curious and often contradictory experiments on this subject will be found in The 

 Gardener s Magazine, vols. ii. and iii. 



2307. Other compounds. Besides these compounds of the alkaline earths and alkalies, 

 many others have been recommended for the purposes of increasing vegetation ; such are 

 nitre, or the nitrous acid combined with potassa. Sir Kenelm Digby states that he made 

 barley grow very luxuriantly by watering it with a very weak solution of nitre ; but he is 

 too speculative a writer to awaken confidence in his results. This substance consists of 

 one proportion of azote, six of oxygen, and one of potassium ; and it is not unlikely 

 that it may furnish azote to form albumen or gluten in those plants which contain 

 them ; but the nitrous salts are too valuable for other purposes to be used as manures. 



