Phosphorous, Hypophosphoric and Phosphoric Acids. 101 



II. The Estimation of Hypophosphoric Acid in the 

 Presence of Phosphorous and Phosphoric Acids. 



Since the hydrolysis of hypophosphoric acid gives an 

 equimolecular mixture of phosphorous acid and phos- 

 phoric acid according to the equation: 



H 4 P 2 6 + H 2 = H3PO3 + H 3 P0 4 , 



it is obvious that the estimation of unknown quantities 

 of hypophosphoric acid can be accomplished by first 

 hydrolyzing completely and then estimating the phos- 

 phorous acid so formed by the method described in the 

 foregoing section. Hypophosphates can be quantita- 

 tively hydrolyzed, as was first shown by Amat, 19 by 







Table VIII. 









Estimation of Hypophosphoric Acid. 





Iodine 



solution 1029 N/50. 



Thiosulphate 



solution 1088 



N/50. 



N£uH,PA 



Iodine 



Na^O, 









solution 



solution 



solution 



H 4 R0 8 



H 4 P 2 6 



Found 



taken 



taken 



required 



found 



taken 



% 



cm 3 



cm 3 



cm 3 



grm. 



grm. 





20-02 



5000 



28-96 



003233 



003245 



99-63 



2500 



5000 



24-37 



004042 



004053 



99-73 



3500 



5000 



15-27 



005648 



0-05674 



99-54 



40-00 



5000 



10-62 



0-06467 



0-06484 



99-74 



45-00 



50-00 



5-91 



007298 



007295 



10004 



•evaporating the solution to dryness with concentrated 

 hydrochloric acid. Phosphorous acid is remarkably 

 resistant toward atmospheric oxidation 20 and under these 

 ■conditions undergoes no loss of reducing power. 



Table VIII gives the results of a series of analyses, by 

 this method, of measured portions of a hypophosphate 

 solution, which was prepared of definite strength by 

 weighing out the very stable, and beautifully crystalline, 

 acid sodium hypophosphate, Na 2 H 2 P 2 6 .6H 2 0, using a 

 sample of the salt which had been carefully purified by 

 seven recrystallizations. In these experiments meas- 

 ured portions of the solution were evaporated nearly to 

 dryness in small beakers over the steam bath. To each 

 beaker 50 cm 3 of hydrochloric acid was then added, and 

 the liquid again evaporated as before. To insure com- 

 plete hydrolysis the treatment with hydrochloric acid 



10 Comptes rendus, 111, 676, 1890. 



S0 Sieverts, Zs. anorg. Chem., 64, 32, 1909. Luther and Plotnikow, Zs. 

 iphys. Chem., 61, 513, 1908. 



