Phosphorous, Ilypophosphoric and Phosphoric Acids. 95 



set aside in the dark for periods varying from 2 to 24 

 hours, 11 after which the iodine remaining was titrated 

 with standard arsenite, using starch as indicator. 



The results are fairly accurate but show, throughout, 

 a small positive error. That this was chiefly due to an 

 interaction between the iodine and bicarbonate is proved 

 by Table III, which gives the results of a series of blank 







Table III. 









Error due to Iodide and lodate Formation. 





Iodine 



solution 0-9438 N/50. 



Arsenite 



solution 1-000 



N/50. 





Iodine 





As 2 3 



Iodine 



Volume 





solution 



Time 



solution 



total 



N/50 Iodine 



KHC0 3 



taken 



hours 



to bleach 



to color 



absorbed 



grm. 



em 3 





cm 3 



cm 3 



cm 3 



2 



4905 



2 



45-35 



4915 



104 



^* 



4900 



2 



4600 



4907 



0-31 



5 



4900 



2 



45-20 



4903 



1-08 



In solution-}- 













em 3 













5$ 



4900 



2 



4618 



4907 



013 



100$ 



4900 



2 



4400 



4910 



234 



5 



4900 



2 



44-88 



49-10 



1-46 



10 



4900 



2 



45-90 



5010 



1-39 



* One drop of dilute HC1 added after the bicarbonate. 



f The solution was prepared by dissolving 250 grams of potassium 

 bicarbonate in a liter of water, and thoroughly saturating the liquid with 

 carbon dioxide. 



$ This portion of the bicarbonate solution was further treated with a 

 current of carbon dioxide gas for 20 minutes just before using. 



experiments in which no phosphorous acid was present, 

 but which in other respects were conducted like those of 

 Table II. The solutions of iodine and of thiosulphate, 

 however, were made fiftieth normal, so that small losses 

 of iodine could be detected with greater certainty, and 

 the influence of the hydroxyl-ion concentration of the 

 solution was tested by employing varying quantities of 

 bicarbonate (1 to 25 grams), and by saturating the solu- 

 tion in some cases with carbon dioxide before mixing with 

 the iodine. 



As the results show, there was in every case a marked 

 loss of iodine. This is easily explained, for it is known 

 that iodine on standing with potassium bicarbonate 

 forms a little iodide and iodate with consequent loss of 

 titrable iodine. Washburn mentions this reaction as a 



11 By heating in a pressure flask at 70°, Sieverts was able to complete 

 the oxidation within 30 minutes. 



