C. R Munroe on the estimation of Phosphoric Acid. 33 L 



the alumina. These experiments are sufficient to show that 

 phosphoric acid may be determined with extreme precision in 

 the alkaline phosphates by the method above given, but the 

 method applies with advantage only to these salts. On the 

 other hand it must be remembered that many phosphates may 

 be decomposed by fusion with the alkaline carbonates and the 

 phosphoric acid then determined as above, so that in fact the 

 method applies in perhaps the greater number of cases which 



§ 2. Rose's* method for the separation of phosphoric acid by 

 means of mercurous nitrate and subsequent estimation in the 

 form of pyrophosphate of magnesia has been mucli used. It 

 will, however, be acknowledged that it has some serious defects. 

 It is tedious, the many operations required increase tlie chances 

 of error, and the fusion of mercurous phosphate with the mixed 

 carbonates exerts, according to Eose, a sensible action upon tlie 

 platinum crucible. Nevertheless the perfect separation which 

 It gives is a strong recommendation of the method. 



It appeared possible that a valuable modification of this pro- 

 cess might result from the addition of mercuric oxide in the 

 manner already employed in the alumina process above de- 



The experiments were executed in the following manner. 

 To a boiling solution of the phosphate mercurous nitrate was 

 added in slight excess. This threw down a lemon-yellow 

 colored, crystalline precipitate of nitro-mercurous phosphate 

 which adhered to the sides of the beaker when touched by the 

 stirring rod. Mercuric nitrate was then added and finally sodic 

 Jiydrate until a slight precipitate of mercuric oxide was obtained 

 which remained undissolved. The mixture of the two salts 

 was found to be insoluble in both hot and cold water, and to 

 wash like sand. 



. The next step was to find a readier means of treating the 

 nitro-mercurous phosphate. 



. ft was first proposed to dissolve the washed and dried precip- 

 itate in chlorhydric acid and titrate with potassic permanganate 

 so as to oxidize the mercurous to the mercuric salt. This pro- 

 cess faded. The salt was then treated with sulphunc acid, 

 ^he final reaction was perfectiv sharp, but the results were not 

 satisfactory. f .. r 



. These results having proved that nothing was to be gained 

 tL -^ direction, I tried to remove the mercury b;^ decomposing 



° nitro-mercurous phospha^ 



ammonio-magnesian solution. On examining the 

 * Traite de Chimie Analytique, ii, 708. 



