D. A. Kr eider — Iodine Titration Voltameter. 



beaker, and the supernatant acid of the cell washed out the 

 iodine completely. 



A burette of 50 cc capacity was employed. This burette was 

 carefully calibrated and was found to be surprisingly accurate. 

 Its error indicates an extremely minute and regular taper of 

 the tube and the graduations are such as to permit of accurate 

 readings to 0'02 cc . In fact I have felt considerable confidence 

 in reading it to O01 cc . This, with the strength of solution 

 employed, was equivalent to about 0'l mg of -silver. In the 

 earlier determinations, when more than 50 cc of the thiosulphate 

 were required, the burette was in some cases 2 



refilled, which, of course, multiplied the error 

 of reading. In other cases, where the amount 0/=^ 



of thiosulphate was approximately known, a 

 sufficient quantity was added to the beakers 

 from calibrated pipettes of various size, so 

 that the additional amount required should be 

 less than 50 cc . This is, of course, less exact 

 and impractical as well, unless the amount 

 required is approximately known. 



In the later determinations a bulb burette, 

 fig. 2, was employed. This contained 6 bulbs, 

 each of approximately 25 cc capacity, connected 

 by small tubes of about 2 to 3 mm internal 

 diameter. At about the middle of these tubes 

 marks were etched in such a way as to permit 

 readings without error of parallax. The 

 smallness of the tubes prevented filling the 

 burette from the top and to avoid the uncer- 

 tainty of rubber connections a small side tube, 

 also about 2 to 3 mm , terminating in a funnel, 

 o, was sealed on and supported by a section 

 of cork as shown. A finger placed on a as 

 the liquid is poured into b regulates the flow, 

 so that air bubbles are not carried along and 

 the burette is filled quietly and accurately. 

 Inclining the discharge tube, as shown, is of 

 great advantage in preventing any of the 

 grease from the cock soiling the interior of 

 the burette, a very troublesome feature of the usual burette. 



The readings of this burette are naturally extremely accurate. 

 It was employed in bleaching the larger part of the iodine. 

 Experience enabled me to judge from the color about when 

 the remaining iodine was less than that bleached by the con- 

 tents of one bulb. If there was any difficulty in judging this, 

 a comparison beaker of iodine solution could be employed. 

 At any rate the 50 cc burette, with which the titration was com- 



C^n 



