184 Proceedings of Indiana Academy of Science 
This consisted in washing the deposits with water, placing the electrode 
in a platinum dish, and drying both in an electric furnace in which 
the temperature was maintained at approximately 250° C. by means 
of a pyrometer. While wet, the peroxide did not show any tendency 
to scale off during handling; but as soon as dried, it often did not 
adhere well. By drying in the platinum dish, any particles falling off 
were saved, since the dish and electrodes were weighed together. 
It was planned to determine the weight of lead deposited at the 
cathode according to the method of Stahler and Alders,’ that is, by 
obtaining the increase in weight of the mercury cathode after having 
decanted the electrolyte and washed the amalgam with water, alcohol 
and ether. Although it is stated that this procedure gives very good 
results, it was not found possible to handle the amalgams in this way 
without having marked evidence of oxidation on the surface of the 
amalgam, even with only a few hundredths of a gram of lead present. 
Sometimes a black scum formed on the surface, which was easily lost 
in the washing by decantation. Some of the preliminary results were 
obtained in this way, but the method was changed for one proving more 
satisfactory. 
The procedure adopted consisted essentially in the replacement of 
the lead in the amalgam by another element, thus bringing the lead into 
aqueous solution from which it could be precipitated.” This was accom- 
plished by washing the amalgam with water by decantation and then 
adding 25 ce. of a 10 per cent solution of copper nitrate. The solu- 
tion remained on the amalgam from 15 to 24 hours, after which it was 
decanted and the resulting amalgam washed with water. Copper is 
less soluble in mercury than lead, and most of the determinations showed 
considerable brownish-red material in the beaker containing the amal- 
gam, after standing in contact with the copper nitrate for several hours. 
This was found to be largely copper, along with some mercury, and 
the solution was always filtered from this precipitated matter. To the 
filtrate two or three drops of acetic acid were added, the solution heated 
to somewhat less than boiling, and the lead precipitated with potassium 
dichromate. The precipitate was handled and weighed according to the 
directions of Scott. 
General Procedure. The arrangement and manipulation of the sil- 
ver coulometer followed rather closely the suggestions of Richards and 
Anderegg,’ a porous porcelain cup and recrystallized silver nitrate being 
used. All the precautions noted in their papers were not followed; such 
as corrections for the amount of electrolyte included in the cathode 
deposit and protection from dust during electrolysis, since the nature 
of the present work did not seem to warrant it. 
Each determination was made by placing 30 to 50 g. of mercury 
in each of the glass cells and adding 100 ec. of the solution of lead 
nitrate to be electrolyzed. The platinum foil anodes were suspended 
in the electrolyte about 1.5 cm. above the surface of the mereury. In- 
1 Loe. cit. 
* Mellon and Reinhard—-See following paper. 
%’ Standard Methods of Chemical Analysis, p. 236 (1917). 
4J. Am. Chem. Soc. 37, 7 675 (1915). 
