258 



THE SOUTHERN PLANTER 



of the animal matter. When whole bones 

 are applied as manure, they undergo de- 

 composition in the soil so slowly, that 

 their effect is at first scarcely perceptible ; 

 and it is only after years of exposure, that 

 the full benefits resulting from their ap- 

 plication are experienced. By breaking 

 the bones into small pieces, and thus ex- 

 posing a larger surface, something is gain- 

 ed ; and a still greater gain is effected by 

 using the bones in a fine state of division, 

 as in bone dust. But even here the ben- 

 efit is not so immediate, or, at first, so 

 marked, as we are led to expect, from a 

 knowledge of their composition. This 

 arises from the extreme insolubility of the 

 phosphate of lime contained in the bones; 

 the same remark is applicable to the min- 

 eral phosphate of lime, to bone ash, and 

 the bone black of the sugar-refiners. It 

 matters not how finely they may be divi- 

 ded mechanically, pure water has no effect 

 upon them ; and the weaker acids* such 

 as acetic (vinegar,) and carbonic, have 

 very little. Hence when they are applied 

 to the soil, in which the principal solvent 

 is water very slightly charged with car- 

 bonic acid, they maybe regarded as •al- 

 most inert, and yield their phosphates 

 with extreme slowness. 



But if bone dust, or either of the other- 

 phosphates mentioned above, be subjected 

 to the action of muriatic acid, a complete 

 solution of the whole of the phosphate of 

 lime takes place, and if to this solution we 

 add an alkalie, such as potash or ammo- 

 nia, until the acid is completely neutral- 

 ized, the phosphate of lime will again as- 

 sume the solid form, but in an exceeding- 

 ly fine state of division ; in other words, 

 it becomes precipitated phosphate of lime. 

 Chemically this precipitated phosphate is 

 the same as the bone phosphate, — it is 

 composed of lime and phosphoric acid, 

 in the very same proportions that they are 

 found in bones, or in mineral phosphate; 

 but in consequence of its lightness and 

 extreme fineness of division, its proper- 

 ties with respect to solvents are essen- 

 tially different. The precipitated phos- 

 phate is insoluble it is true, but when 

 the water is acidulated with a weak acid, 

 as acetic acid, it is readily soluble, and 

 hence when it is applied to the soil, water 

 charged with carbonic acid dissolves more 

 or less of it, and thus it finds its way into 

 the circulation of plants. 



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 neutral 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 are present in 

 every fertile soil, whether naturally or by 

 the addition of these bases to it, the free 

 phosphoric acid unites with one or 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, in- 

 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 

 for any length of time in the soil as such ; 

 neutral phosphates are formed, but these, 

 although for the most part insoluble in 

 water, are 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 



O DO 



use of the superphosphate, and it is upon 

 this, that its superior advantage over 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 certain 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, forming sulphate 

 of lime, or plaster, — leaving the phospho- 

 ric acid in the form of superphosphate of 

 lime. 



In preparing this substance, very much 

 depends upon the proportion of sulphuric 



