Nelson. — Tricalcic Phosphate in Carbonic-acid Solutions. 



575 



Method. 



A small quantity of Merck's pure precipitated tricalcic phosphate is 

 placed in the apparatus, and about 330 c.c. of water added. After satura- 

 tion at the required pressure with carbon dioxide, the whole is shaken for 

 five hours, then allowed to stand for eighteen hours, after which the solu- 

 tion, which is quite clear and bright, is run off through the needle valve. 

 The phosphate is estimated by an adaptation of Woy's molybdate method 

 (Chem. Zeit., vol. 21, p. 442). The phosphate is precipitated as ammonium 

 phosphomolybdate, which, after solution in ammonia and reprecipita- 

 tion by nitric acid, is heated in a Gooch crucible to dull redness. By 

 this means a dark-blue substance is formed, phosphomolybdic anhydride, 

 24Mo0 3 .P 2 5 , which contains 3-946 per cent, of P 2 3 . 



Experimental. 



Series I. — The first series of experiments performed in the glass 

 apparatus was unsatisfactory, but showed an increase of solubility with 

 increase of pressure. 



Series II. — About 0-75 gram of tricalcic phosphate was taken in 330 c.c. 

 of water. The range of pressures was from 0-5 atmosphere up to 18 atmo- 

 spheres, §X half and 1 atmosphere intervals. The solubility of the phos- 

 phate, in terms of grams of P 2 5 per litre of solution, varied from 0-0995 

 at 1 atmosphere to 0-3804 at 18 atmospheres, the curve being shown in 

 fig. 2. The general trend shows a regular increase of solubility with 

 increase of pressure. 



2 3 4 5" 6 



Fig. 2. 



During this series of runs the enamel with which the apparatus was 

 lined began to flake off from the interior, until at the end practically none 

 remained. The surface was only very slightly attacked, and on no occa- 

 sion could any appreciable blue cuprammonium salt be obtained on adding 

 ammonium hydroxide and filtering. The tube was cleaned thoroughly 

 and re-enamelled. 



