370 Peters and Moody — Determination of Per sulphates. 



then potassium bicarbonate, and titrating with iodine to a color 

 without starch. In all cases, save that of the potassium car- 

 bonate, the color of the first drop of iodine solution added 

 was destroyed, and from 0-06-0'19 cm3 were necessary to bring 

 the permanent iodine color. The results of these experiments 

 are given in Table II. 



Table II. 



Arsenic solution No. 1. 



Arsenite 



solution 



taken. 



era 3 . 



25 



25 



25 

 25 



25 

 25 



25 

 25 



NaOH 



present. 



grm. 



KOH 



present. 



grm. 



K 2 C0 3 



present. 



grm. 



Iodine 

 solution 

 required 

 to bring 



color. 



cm 3 . 



25-40 



Remarks. 



25 . 36 ) NaOH by Ca0 2 H 2 , aver- 

 ) age of 4 experiments, 

 25-29 KOH by alcohol. 

 25-07 KOH by Ba0 2 H 2 . 



Arsenic solution No. 



2554 



6 _. 25-42 



6 ._ 25-30 



6 25-56 



4 ._ .. 0-12 



6 ._ .. 0-06 



6 .. 0-06 



6 ._ 0-19 



2 .. 0-07 



6 0*02 



KOH by alcohol. 

 KOH by Ba0 2 H 2 . 



NaOH by Ca0 2 H 2 . 

 NaOH bv alcohol. 

 KOH by" alcohol. 

 KOH by Ba0 2 H 2 . 

 KOH by Ba0 2 H 2 



Potassium carbonate proves to be inefficient as a substitute 

 for an alkaline hydroxide, but by using definite amounts of the 

 hydroxide, and introducing a correction for the oxidation 

 determined by the blank tests, the real oxidizing effect of the 

 persulphate upon the arsenite may be deduced. Table III 

 contains the values found by Griitzner's process thus corrected, 

 as well as uncorrected results. 







Table 



III. 





Ammonium 

 persulphate 







Calculated 



(NH 4 ) 2 S 2 8 

 corrected 



solution 



Arsenite 



NaOH by 



from Iodine 



for oxidation 



taken. 



solution. 



Ca0 2 H 2 . 



actually used. 



in blank. 



cm 3 . 



cm 3 . 



grm. 



grm. 



grm. 



I2'5 



25 



2 



0-1223 



0-1218 



12-5 



25 



2 



0-1223 



0-1218 



12-5 



25 



2 



0-1225 



0-1220 



12-5 



25 



2 



0-1229 



0-1220 



