from Saline Solutions, 233 



in the instance of distilled vinegar. From some descriptions 

 we have even in the works of respectable authors of the me- 

 thods of examining soils, and of detecting this compound, 

 this quality of the solubility of phosphate of lime in acetic 

 acid, might be supposed not to exist. Thus, in an able work 

 on Agricultural Chemistry, it is stated, under the head of de- 

 tecting phosphate of lime in soils, that if the precipitate by 

 ammonia obtained from a solution after the action of muria- 

 tic acid on a sample of soil, is not entirely dissolved by ace- 

 tic acid or vinegar, the presence of phosphate of lime is in- 

 dicated.* Now, this surely is an error, as phosphate of lime 

 is soluble in acetic acid and in vinegar. This is so familiarly 

 known that it hardly requires to be illustrated. It may not, 

 however, be amiss to mention one or two results I have ob- 

 tained. If phosphate of lime be digested in distilled vinegar, 

 and the filtered solution be evaporated, the phosphate I find 

 is recovered, as might be expected, unaltered, excepting in 

 form. If the evaporation be carried on rather rapidly, the 

 phosphate will be obtained in minute, thin, irregular plates 

 possessing a good deal of lustre, and shewing a tendency to 

 crystallization. If the process be carried on slowly, and with 

 care, then the phosphate will be procured in the form of 

 prisms, some of them distinctly hexahedral. 



In commencing these observations, I expressed the belief 

 that the precipitation of one earth by another, might be ap- 

 plicable not only to explain certain effects in Nature, some 

 of which I have alluded to, but might also be made useful in 

 chemical analysis. At present it would be premature to 

 dwell on this part of the subject ; I may hereafter recur to 

 it. As an example I may notice the precipitation of alu- 

 mine by lime and carbonate of lime, the non-precipitation of 

 magnesia by these, excepting when in solution by means of sul- 

 phuric acid, and the precipitation of phosphate of lime by lime, 



* Lectures on Agricultural Chemistry, by J. F. W. Johnston, P.R.S. Edi- 

 tion of 1844, p. 552. 



VOL. XLIII. NO. LXXXVI. — OCTOBER 1847. Q 



