182 Separation and Estimation of Phosphoric Acid. 



* 6. The C. modification of phosphoric acid may be separated 

 from magnesia by dissolving the phosphate in chlorohydric acid, 

 adding carbonate of baryta and allowing the whole to stand for 

 some time. The supernatant liquid contains all the magnesia, 

 while the phosphoric acid unites with the baryta. 



7. The phosphates of lime, baryta, strontia and magnesia, 

 are not completely decomposed by fusion with alkaline carbon- 

 ates, but if the phosphate of magnesia be fused with six times 

 its weight of carbonate of soda the resolution is very nearly 



complete. 



8. Phosphate of magnesia may be perfectly decomposed ac- 

 cording to Weber by fusion with a mixture of equal equivalents 

 of the carbonates of soda and potash. The same however is 

 by no means the case with the phosphates of lime, baryta and 

 strontia. 



9. Phosphate of lime cannot be decomposed by fusion with 

 hydrate of potash, or by boiling with a solution of carbonate of 

 soda. If the phosphates however have not been previously igni- 

 ted, the decomposition is nearly complete in a cold concentrated 

 solution of the alkaline carbonate. 



10. The phosphates of zinc, protoxyd of manganese and per- 

 oxyd of iron may be perfectly decomposed by simple fusion with 

 carbonate of soda. The phosphate of oxyd of copper is partly 

 reduced to a suboxyd, which however appears to contain no 

 phosphoric acid ; on the other hand the solution filtered off from 

 the insoluble residue still exhibits traces of copper. 



11. The phosphates of the oxyds of uranium and chromium 

 • may be completely decomposed by fusion with a mixture of car- 

 bonate of soda and cyanid of potassium. (For the details of 

 the method we must refer to the original memoir.) 



12. The phosphates of magnesia and soda cannot be completely 

 decomposed by means of sulphuric acid and alcohol. On the 

 other hand, it is well known that in this manner the separation of 

 phosphoric acid from lime may be easily and perfectly effected. 



13. The phosphates of alumina and peroxyd of iron do not 

 admit of a perfect decomposition by means of sulphuric acid and 



•subsequent addition of sulphate of ammonia and alcohol. The 

 phosphate of magnesia may however be decomposed in this man- 

 ner, though a small portion of the phosphoric acid is always vol- 

 atilized by heating with sulphuric acid, hence the method is not 

 to be recommended. 



14. The following is the method recommended by Rose for 

 the separation of phosphoric from all bases. The phosphoric 

 acid combination is to be dissolved in a moderate quantity of nitric 

 acid, and the solution brought into a porcelain capsule. Metallic 

 mercury is then to be added in such quantity that a small por- 

 tion always remains undissolved by the free acid, and the whole 



