D. A. Kr eider — Iodine Titration Voltameter. 9 



ment. The iodide was roughly weighed. No correction was 

 made for the blank determinations, nor was special care taken 

 to maintain exact constancy of temperature. 



Table TV shows the results of the only two determinations 

 that were made by three of the iodine voltameters in series 

 with each other and with one normal silver gravimetric volta- 

 meter. The original readings of the burettes for the required 

 thiosulphate is given in the 6th column. In the 7th column 

 is given the value corrected for the blank determinations. A 

 number of blank determinations for the small cell, when 

 5 grams of iodide were used, gave, with the blank shown in 

 (2), an average value of O07 cc of thiosulphate, which is the cor- 

 rection applied to all of the small cells. The large cell, with 

 10 grams of potassium iodide, showed an average value for a 

 blank determination of - 21 ec of thiosulphate. This is three 

 times instead of twice the value of the small cell, as would be 

 expected were the result due to traces of iodate in the iodide. 

 The uncertainty as to the amount of iodine liberated by iodate, 

 or by dissolved oxygen, or by possible oxidizing impurities of 

 the acid, make it rather more desirable to employ known 

 weights of the iodide and known volumes of the acid and then 

 to correct for the blank determination, than the alternative of 

 securing absolute freedom from these extra sources of libera- 

 tion of iodine. 



In the silver voltameter employed, the cathode was a plati- 

 num bowl about 8 cm in diameter and 3'5 cm in depth. The 

 anode was a silver disc, 5'8 cm in diameter, 0*8 mm thick, and sup- 

 ported by three platinum wires bent over its edges. This was 

 wrapped in filter paper. The solution was made up of 

 20 grams of pure silver nitrate, dissolved in 106 cc of distilled 

 water. The deposited silver was washed with water and 

 allowed to stand under water over-night. Then washed again 

 with water, finally with absolute alcohol and heated for 4 hrs. 

 in an oven at 160°. Then allowed to cool for an hour in a 

 desiccator before weighing. 



Table IV. 



1 Electrodes, 

 cm. 



Distance 



between 



Electrodes, 



cm. 



( 1-6x2-7 

 •^ 1-6x2-7 



j (2-5x6-0 



1 (1-6x2-7 

 - 1-6x2-7 

 (2-5x6-0 



2 

 5 







2 

 5 

 5 



KI 

 grms. 



Amp. 

 (approx.) 



5 in 7-5 



8-5 

 20 



7-5 

 7-5 



20 



0-5 



0-0 



e— 





0-058 152-07 

 0-058 152-06 

 0-017 152-19 



0-00 



0-058 



0-017 



2 go 



152-00 

 151-99 

 151-98 



0-06 

 156-40 

 156-551 156-341 



156-33 



Silver 



equivalent, 



grms. 



1-63386 

 1-63375 

 1-63364 



1-68042 

 1-68053 



Silver 



(in vac. 



ag- 



voltameter, 



grms. 



1-63236 



1-67934 



Difference. 



Grms. of 

 silver. 



0-00150 

 0-00139 

 0-00128 



0-00106 

 0-00119 



0-092 

 0-085 

 0-078 



0-063 

 0-071 



