Peters and Moody — Determination of Per sulphates. 369 



ture. In the experiments recorded in section C, the air above 

 the liquid was replaced by carbon dioxide. It is seen that the 

 results of the experiments given in the three sections of the 

 table agree quite closely with one another, and the average of 

 these experiments gives a value to the persulphate solution of 

 ■0-1217 grm. of the salt in 12*5 cm 3 . 



Experiments were made in blank to discover the amount of 

 ferrous salt oxidized in 11 hours by other agencies than the 

 persulphate. The amount of oxidation in that time, however, 

 was too small to be detected, but, when the solution was allowed 

 to stand 36 hours a slight oxidation was noticed, which if cal- 

 culated as persulphate, would be equivalent to 0*0006 grm. 

 The correction for il hours standing, upon this basis, therefore, 

 would be 0*0002 grm., which is obviously so small that it may 

 be disregarded. This absence of any significant oxidation of 

 the ferrous salt was undoubtedly due to the fact that the solu- 

 tion of ammonio-ferrous sulphate had been standing some time 

 before standardizing and was devoid of any active oxygen. 



Method of Griitzner. 



In testing the value of the persulphate solution according to 

 the method of Griitzner,* the mixture containing the persul- 

 phate, standard arsenite solution, and sodium hydroxide was 

 raised to the boiling point, cooled, faintly acidified with sul- 

 phuric acid, then made alkaline with potassium bicarbonate, 

 and after adding a large excess of the last, the arsenite remain- 

 ing unoxidized was titrated by iodine. Experiments made in 

 blank, that is experiments in which the mixture of arsenite and 

 alkaline hydroxide was raised to the boiling point, cooled, 

 made acid with sulphuric acid, then alkaline with potassium 

 bicarbonate, and titrated with iodine, showed a deficiency of 

 arsenious acid as compared with the experiments, similarly 

 conducted, in which the mixture was not subjected to heat. 

 The effects of various specimens of sodium and potassium 

 hydroxide were tested in the process — sodium and potassium 

 hydroxide made by the alcohol process, potassium hydroxide 

 by the barium hydroxide process, sodium hydroxide especially 

 prepared from sodium carbonate and calcium hydroxide — as 

 well as a specimen of potassium carbonate. In the case of all 

 but the potassium carbonate, more or less oxidation was ob- 

 served, sometimes trifling, sometimes considerable. The same 

 specimens of potassium and sodium hydroxides and potassium 

 carbonate were tested in the absence of the arsenite solution, 

 by dissolving them in water, heating the solution to the 

 boiling point, cooling, adding sulphuric acid in faint excess and 



* Loc. cit. 



