of Organic Bodies. 19 



suits, consisting of the earthy phosphates in combination with 

 the alkalies, are formed. Most of them are analogous in com- 

 position to the ammonio-phosphate of magnesia, but contain 

 a fixed alkali instead of ammonia. The extremely imperfect 

 decomposition which ensues on fusing the phosphates of lime 

 and magnesia with alkaline carbonates, depends in most cases 

 upon the formation of these double salts. 



Their formation is undoubtedly the cause of the quantities 

 of the alkalies being estimated incorrectly, and in too small 

 proportion, in many investigations on the determination of the 

 inorganic constituents of organic substances, because their 

 presence in the muriatic solution could not have been expected. 



The mass obtained by evaporation is moistened with muriatic 

 acid and then treated with water. Usually a small quantity 

 of silica remains undissolved, which is separated by filtration 

 and its weight determined. The liquid is then neutralized 

 with ammonia. The precipitate contains phosphoric acid in 

 combination with lime, magnesia and peroxide of iron. It is 

 well known that when phosphate of magnesia has been heated 

 to redness, and is then dissolved in an acid, it cannot be com- 

 pletely precipitated by ammonia : the error, however, arising 

 from this source is of only slight importance; because the 

 carbonized mass has been heated for a very long time with 

 muriatic acid, by which means, as is well known, the pyro- 

 phosphate of magnesia is almost entirely converted into the 

 c-phosphate of magnesia. The extremely small quantity of 

 magnesia which remains in solution is, however, determined 

 in the further progress of the analysis. 



The phosphates which have been precipitated by the am- 

 monia are dissolved in nitric acid, and treated with mercury 

 to separate the phosphoric acid from the bases. The dried 

 mass is treated with water, and the mercurial salt removed 

 from the solution by muriate of ammonia and ammonia; the 

 lime is then precipitated by an alkaline oxalate, and the mag- 

 nesia by phosphate of soda. Wherv peroxide of iron is mixed 

 with the earths, it is separated by the usual methods. The 

 insoluble mercurial residue containing phosphoric acid is fused 

 with carbonate of soda, and the fused mass treated with water. 

 Should any peroxide of iron then remain undissolved, it is 

 separated by filtration, dissolved in muriatic acid, and preci- 

 pitated by ammonia. The liquid which has been separated 

 from the peroxide of iron by filtration, and which contains 

 phosphate and carbonate of soda, is supersaturated with 

 muriatic acid and then with ammonia, and the phosphoric 

 acid precipitated by sulphate of magnesia. The amount of 

 phosj)horic acid is calculated from the weight of the ani- 



C2 



