82 Recent Publications on Manures. 



the other organic matter at 36\ per cent. Bones are also prin- 

 cipally valuable on account of the phosphate of lime they con- 

 tain ; and the apatite, or native phosphate of lime, from Spain is 

 about to be introduced as a substitute. How phosphate of lime 

 is rendered soluble, is not yet known ; perhaps the salts and gases 

 in thewater,ortheelectricity evolved in the chemical changes going 

 on in the soil, may assist. Phosphate of magnesia, not being 

 discovered native yet, is probably got by carbonate of magnesia 

 being absorbed, decomposed, and united to phosphoric acid in 

 the plant." It is possible that part of both these phosphates 

 may be got in that way : the phosphoric acid of the soil, which, 

 Liebig says, is found as a constituent of all soils, may be absorbed 

 either in that state or as phosphate of ammonia, and united to 

 magnesia there, or to the carbonate of lime held in solution in 

 the sap by carbonic acid. The phosphate of lime, however, in 

 urine, Professor Thomson says, is held in solution by an excess 

 of phosphoric acid. Bones also contain the phosphate in the 

 state of a superphosphate, or an excess of acid there also. To 

 procure phosphate of lime, it is necessary to add pure ammonia, 

 both to the urine and the calcined bones, to take up the excess 

 of acid, before the phosphate of lime can be precipitated. The 

 acetic acid of the urine also, he thinks, keeps the phosphate in 

 solution. From the excess of acid, therefore, in the superphos- 

 phate of lime in the bones themselves, assisted by the phos- 

 phoric acid of the soil, or by acetic acid, the phosphate of 

 lime is most likely to be dissolved and rendered fit for absorption. 

 Professor Johnston thinks the carbonic acid of the soil may 

 dissolve sufficient of the phosphates, as he found one gallon of 

 water saturated with carbonic acid to take up 30 grs. of phos- 

 phate ; it will also furnish silica, he says, as it absorbs the alkali 

 of the insoluble silicates of the soil, and liberates the silex in 

 a soluble state. Apatite of lime, Thomson classes as a sub- 

 phosphate, and it will therefore be more difficult of solution, 

 from its inferior quantity of phosphoric acid, about one third 

 part less than that of the phosphate itself. For grain crops 

 the phosphates will be much wanted, and some have said 

 they are greatly wanted for turnips also. The analysis, how- 

 ever, of the turnip, by Dr. Madden, gave only a small quan- 

 tity of hydrosulphate of lime. Many repeated analyses of 

 plants, grown in different circumstances, may be needed, before 

 we can decide on what constituents manures ought to furnish : 

 what, however, is not needed, or rejected as excrement by one 

 crop, may be beneficial to the next in the rotation. In bones, 

 the gelatine, from the great quantity of ammonia it furnishes, is 

 very valuable; and the ammonia, and lithicor uric acid, together 

 with the saline substances, about 70 per cent in the guano, 

 must be an important part of its value. Mr. M'Donald, in the 



