Excerpt from The Southern Planter, Vol. 17: Devoted to Agriculture, Horticulture, and the Household Arts; May, 1857

The superphosphate of lime is a com pound of lime and phosphoric acid which is soluble, and contains'more phosphoric acid in proportion to the lime, than is found in the neutrai or bone phosphate; it may be regarded as a compound of neu tral phosphate, with free, or uncombined phosphoric acid, in which the neutral phosphate is soluble, just as it is in muri atic acid. Whenever this compound comes. In contact with the various bases, such as lime, potash, etc., which arepresent in every fertile soil, ' whether naturally or by the addition of these bases to it, the free phosphoric acid unites with one 01 more of them, when the neutral phosphate is precipitated, and becomes insoluble phos phate of lime. But as it is in the form of a precipitated phosphate, it is in a con dition to be acted upon by the ordinary solvents of the soil. The free acid, by its union with the bases, forms phosphates which are also in a fine state of division: if it meets with lime and magnesia, ih soluble salts result - if with the alkalies, soluble phosphates are found. It is im possible that the superphosphate, unless applied to a sandy waste, should continue f01 any length of time in the soil as such; neutral phosphates are formed, but these, although for the most part insoluble in water, a1e readily acted upon by the sol vents in the soil, and are consequently immediately available to growing crops. This fact first led Liebig to suggest the use of the superphosphate, and it is upon this, that its supe1ior advantage ov11 bone dust, bone black, and mineral phosphate depends.

The superphosphate of lime is not a natural, but an artificial product; it may be formed from the natural phosphate by the addition of a certa1n proportion of phosphoric acid, or the subtraction of an equivalent proportion of lime from it. The latter course is, the'only practicable one. The substance used to separate the lime is sulphuric acid; this being a stronger acid than phosphoric, and Having a powerful affinity for lime, it will, when applied to neutral phosphate of lime, take away a part of the lime, formlng sulphate of lime, or plaster, - leaving the phospho ric acid in the form of superphosphate of lime.

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