MODERN HIGH FARMING. 67 



If in the same way we add magnesia and ammonia, the phosphoric 

 acid will at once fly to them, and, as ammonia phosphate of mag- 

 nesia, will fall to the bottom; and so on, until one after the other, 

 we have secured all the ingredients which the solution contained. 



The ammonia-phosphate of magnesia which has been deposited 

 as a sediment, is separated from the liquid by passing the whole 

 through filtering paper, from which, after it has become dry, the 

 powder left behind is easily collected. 



This powder is then submitted to the most intense heat, and is 

 thereby transformed into calcined or pyro-phosphate of magnesia, 

 the object of the burning process having been, to drive off the 

 ammonia and any other foreign bodies, which have not, like magne- 

 sia-phosphate, the property of resisting extreme temperatures. 



Pyro-phosphate of magnesia, being composed of known parts of 

 phosphoric acid and of magnesia, we accurately weigh our calcined 

 product; and, supposing, for the sake of illustration, its weight to be 

 fifty grains, we immediately know that the substance analyzed 

 contains thirty-two per cent, of phosphoric acid, and by a similar 

 system of calculation, arrive at the equivalent of this quantity in 

 phosphate of lime. 



Before quitting the subject of mineral phosphates, it will be ad- 

 visable to mention the discovery of large deposits in the Island of 

 Alta Velta, near San Domingo, of a mineral which was at first 

 mistaken for phosphate of lime, and as such, shipped in considerable 

 quantities to European ports. 



Upon complete analysis, it was found to be phosphate of alumina 

 and iron, with very little lime, and a huge outcry was raised against 

 it by leading London analysts, who denounced it* as of no value to 

 agriculture. 



The cargoes which had already been shipped were consequently 

 refused by the consignees and thrown upon the market at very low 

 prices; but so great was the prejudice against them, that we have 

 never heard of their having met with any purchasers. The detailed 

 composition of these phosphates is shown in the following analysis, 

 made from a fair and well-selected sample: 



