372 Peters and Moody — Determination of Persulphates. 



Ammonium 



persulphate 



solution. 



cm 3 . 



KI. 



grm. 



H 2 S0 4 

 1: 1. 

 cm 3 . 



Table IV. 



Time 

 of 

 Yolume. heating. 

 cm 3 . minutes. 



A 



Na 2 S 2 3 



required. 



app X/ 10 



cm 3 . 



(NH 4 ) 2 S 2 0, 



calculated 



from sodium 



found. 



grm. 



12-5 



i-o 





25 





10 



10-65 



0-1200 



12-5 



1-0 







25 





10 



10-74 



0-1210 



12-5 



1-0 







25 



B 



30 



10*73 



0-1209 



j 12-5 



1-0 





100 



10 



9-89* 



0-1124 ) 



( 12-5 



l'O 







100 





10 



8-99* 



0-1013 \ 



12-5 



1-0 







100 





30 



10-70 



0-1206 



12-5 



l'O 







100 





30 



10-72 



0-1208 



12-5 



1-0 







100 



c 



30 



10-72 



0-1208 



12-5 



1-0 



05 



25 



30 



10-78 



01214 



125 



1-0 



0*05 



100 





30 



10-81 



0-1218 



12-5 



1-0 



1-0 



100 





30 



10-81 



0-1218 



12-5 



1-0 



1-0 



100 





30 



10-84 



0-1221 





1-0 





100 



D 



30 



o-oo 



o-oooo 



. _ _ _ 



1-0 



1-0 



100 





30 



0-07 



0-0008 







1-0 



l'O 



100 





30 



o-io 



o-oon 







l'O 



1-0 



100 





30 



0-03f 



0-0003 



process is hardly to be recommended, because of the sensitive- 

 ness of the hydriodic acid set free to the oxygen of the air and 

 the oxygen dissolved in the water. The value of 12'5 cm3 of the 

 persulphate solution obtained by the method of Mondolfo, 

 found by averaging the results of experiments in sections A 

 and B (omitting the first two experiments under section B) is 

 0*1207 grm., while that found by averaging the results of ex- 

 periments in section C and deducting the correction given in 

 the experiments under section D is 0*1208 grm. 



Method of JVamias. 



In the process for the estimation of persulphates carried out 

 as described by Namias,:j: a mixture containing 12*5 cm3 of the 

 persulphate solution, 1*0 grm. of potassium iodide, and water 

 sufficient in some experiments to make a volume of 25 cm3 , and 

 in other experiments 100 cm3 , was allowed to stand 11 hours in 

 a stoppered bottle and the iodine set free was titrated by thio- 

 sulphate. After the titration by thiosulphate the mixture was 

 allowed to stand still longer, and 16 hours later the blue starch 

 iodide color which had developed in the experiments with the 



* Color returned. 

 \ Loc. cit. 



f Air over liquid replaced by carbon dioxide. 



