64 PROCEEDINGS OP THE AMERICAN ACADEMY 



Phosphotdngstates. 



In each of the following experiments upon the determination of 

 phosphoric oxide in phosphotungstates 1 gr. of crystallized normal 

 sodic tungstate (Na 2 W0 4 . 2 H 2 0) was dissolved and added to 40 cm. 8 

 of a phosphate solution, the phosphotungstate produced by the addi- 

 tion of acid in measured amount or until the yellow color of the 

 solution indicated its formation, and ammonia added until the precipi- 

 tate first formed redissolved. 



In experiments (67) to (76) inclusive there were added to each por- 

 tion containing the phosphate and tungstate 0.5 gr. of citric acid, 

 hydrochloric acid until the solution became yellow, ammonia until it 

 gave its odor distinctly to the solution, and then 20 cm. 3 of magnesic 

 sulphate mixture. Portions (75) to (79) inclusive were treated in a 

 similar manner, excepting that 5 cm. 3 of strong hydrochloric acid and 

 no citric acid were added to them. The precipitates of (67), (68), 

 (69), and (70) were filtered off on asbestus, washed, and ignited in 

 the manner previously described. The precipitates of (71), (72), (73), 

 and (74) were filtered off on paper, washed with magnesic sulphate 

 mixture, and then with a few centimeters of ammonia, dissolved in 

 hydrochloric acid and reprecipitated with ammonia, a few centimeters 

 of magnesic sulphate mixture being added after the precipitate had 

 settled. The precipitates of (75) to (79) inclusive were filtered off 

 on paper, washed with magnesic sulphate mixture, dissolved in hydro- 

 chloric acid and thrown down again with ammonia, a few centimeters 

 of magnesic sulphate being added after the settling of the precipitate. 

 The second precipitates were filtered off on asbestus, washed, and 

 ignited as usual. 



Mg 2 P 3 7 . P 2 6 found. PA required. Error. ^rrw"*" 



(67) 0.0439 gr. 0.0281 gr. 0.0265 gr. -{-0.0016 gr. +6.04 



(68) 0.0445 gr. 0.0285 gr. 0.0265 gr. +0.0020 gr. +7.55 



(69) 0.0448 gr. 0.0286 gr. 0.0265 gr. +0.0021 gr. +7.92 



(70) 0.0455 gr. 0.0291 gr. 0.0265 gr. +0.0026 gr. +9.81 



(71) 0.0388 gr. 0.0248 gr. 0.0265 gr. —0.0017 gr. —6.41 



(72) 0.0390 gr. 0.0249 gr. 0.0265 gr. —0.0016 gr. —6.04 



(73) 0.0391 gr. 0.0250 gr. 0.0265 gr. —0.0015 gr. —5.66 



(74) 0.0394 gr. 0.0252 gr. 0.0265 gr. —0.0013 gr. —4.90 



(75) 0.0421 gr. 0.0269 gr. 0.0265 gr. +0.0004 gr. +1.51 



(76) 0.0426 gr. 0.0272 gr. 0.0265 gr. +0.0007 gr. +2.64 



f (77) 0.0424 gr. 0.0271 gr. 0.0270 gr. +0.0001 gr. +0.37 



XIII. i (78) 0.0427 gr. 0.0273 gr. 0.0270 gr. +0.0003 gr. +1.11 



[(79) 0.0428 gr. 0.0274 gr. 0.0270 gr. +0-0004 gr. +1.48 



