68 HYPONITRITES ; PEOPEETIES AND PREPARATION BY 



warming to 30"^ and adding enough oxalic acid, in known quan- 

 tity, to decolourise, and finally titrating back with permanganate. 

 The hyponitrous acid is thus oxidised ultimately to nitric acid. 

 The oxalic acid should be a decinormal solution, and the solu- 

 tion of permanganate be volumetrically equivalent to it. Dur- 

 ing the oxidation, much brown manganese hydroxide forms, 

 but this all disappears along with the excess of permanganate 

 when the oxalic acid is added. Ferrous sulphate is unsuita- 

 ble for use in place of oxalic acid. The process is an excellent 

 one. Hantzsch and Sauer have failed to get good results with 

 it and condemn it, but that is because they have unwarrantably 

 deviated from Thum's directions by acidifying the permanganate 

 before adding it to the hyponitrite. Kirschner has also had no 

 success with the process, at the same time getting results widely 

 different from those of Hantzsch and Sauer. His failure is also 

 sufficiently explained by his deviations from Thum's directions. 

 Kirschner added nearly insoluble salts, such as the barium, 

 strontium, or silver hyponitrite, to the potassium permanganate, 

 having thus the base of the salt present and locally the hypo- 

 nitrous acid in excess of the permanganate. He then added 

 the sulphuric acid, apparently immediately, and finally titrated 

 back with ferrous sulphate. 



Taking 5cc. normal hydrochloric acid as the standard, 

 largely diluting it, adding ice and a cream of precipitated silver 

 hyponitrite up to exact consumption of all the hydrochloric 

 acid, making up to lOOcc, and decanting from the bulk of the 

 silver chloride, I have got a solution which, though somewhat 

 turbid with chloride gave, in successive portions of 20cc., all 

 tested within an hour, quantitative results corresponding well 

 with the presence of .155 gram hyponitrous acid in lOOcc, 



