PHOSPHORIC ACID. 18 



and its composition never corresponds to definite proportions. The 

 pure basic phosphate is obtained from the preceding by moistening 

 it with pure syrupy phosphoric acid, and washing it with a great 

 excess of water. The product so obtained remains white on 

 ignition. It is soluble in hydrochloric acid, perchloride of iron, and 

 in acetate of iron, and insoluble in acetic acid. The acid phosphate- 

 of iron is prepared by dissolving the freshly precipitated, air-dried, 

 basic phosphate in pure, syrupy phosphoric acid. Properly pre- 

 pared, and the water abstracted, the solution has an analogous- 

 composition to other acid phosphates ; it is rose-red, and may be 

 converted by means of a large excess of water into free phosphoric 

 acid and basic phosphate. It likewise yields a precipitate on heat- 

 ing. Tartaric, citric, and other non- volatile organic acids prevent 

 the formation of the precipitate ; mineral acids only possess this 

 property but imperfectly. 



7. T]ie PJiosjjliates of Alumma behave in a general way like the 

 phosphates of iron. Wavellite, a crystallized mineral phosphate, is. 

 a phosphate of alumina. Redonda phosphate, which forms an 

 important deposit, consists chiefly of a compound of this nature. 



The phosphates just described are met with in different phos- 

 phatic manures, natural or artificial. The majority of them, such 

 as the alkaline and ammonium phosphates, are only represented in 

 small proportions it is true ; however, one cannot but acknowledge 

 their vast importance from the point of view of the mobility of 

 phosphoric acid in the soil, and in the organism. The only phos- 

 phates found in preponderating amount in manures are the phos- 

 phates of lime. The basic phosphates of lime are spread over 

 numerous points of the globe ; as will be seen further on considerable^ 

 deposits of them exist which are wrought commercially. But these 

 phosphates are more or less mixed with impurities, that is why they 

 serve exclusively as raw material for the manufacture of phosphatic 

 manures, properly so called, which are acid phosphates of lime, 

 or s2iperphos])hates. 



Moreover, various industries supply important quantities of 

 basic phosphates, obtained as bye-products. They deliver them to- 

 manure manufacturers, who use them in making superphosphates., 

 or they dispatch them direct to the farmers (basic slag). 



