370 C. A. Peters — Electrolysis of Sodium Chloride 



ration of the mercury before titration. Of course in such cases 

 the rubber stoppers were first taken out, one at a time, and the 

 inner breaker washed as it was removed from the apparatus. 



Determination of Silver in Mercury. — In the first attempts 

 to estimate the residual silver in the flask after distillation the 

 mercury was driven out completely by cutting off the neck of the 

 distillation flask and heating it — after most of the mercury had 

 been driven out — opening down. The heavy vapor gradually 

 settled out and left the silver adhering to the flask. Solution 

 and precipitation followed. The long time necessary to get the 

 mercury completely out of the flask and the solubility of the 

 silver chloride in acid upon precipitation suggested the follow- 

 ing procedure, which was used in all the work here quoted. 

 The mercury was distilled until only a small globule the size 

 of a pea remained. Then after the apparatus had cooled and 

 the distillate had been emptied from the receiver, the globule 

 remaining in the distilling flask, together with some of the 

 mercury that had collected about the neck of the flask, was 

 poured into a small tared crucible and heated gradually in the 

 crucible until all the mercury had left and then the silver 

 was weighed. In case the globule of mercury was quite rich 

 in silver and some of it stayed behind on the flask, gentle jar- 

 ring caused more mercury to fall to the bottom, and this was 

 used to wash out the last trace of amalgam. A preliminary 

 experiment showed that a few milligrams of silver were com- 

 pletely freed from added mercury by five minutes heating over 

 the Bunsen burner. 



Depth of Mercury in Cell. 



Smith,* IIildebrand,f Goldbaum and Smith:}: recommended 

 the use of the mercury 3 mm above the bottom of the inner cell. 

 Goldbaum § later used about 6 mm . The writer's experience 

 confirms the use of at least 6 mm of mercury to seal the two com- 

 partments. In several experiments when less than 6 mm of mer- 

 cury were used liquid passed from the inner to the outer cell, 

 the speed of the anode being 250-300 revolutions per minute. 

 Faster rotation, 470 revolutions, forced water to the outer cell 

 on some occasions even with 6 mm of mercury above the lower 

 edge of the inner cell. 



Experience with Anode. 



Drying and Heating. — In a number of experiments after 

 the electrolysis of generally 50 cm3 of *1N sodium chloride 

 solution the anode was dried over night in a sulphuric acid 

 desiccator, then heated to a constant weight in a steam oven at 



* Electro-Analysis (1907), 304. \ L. c. 1470. 



t L. c. 451. § L. e. 36. 



