194 Proceedings of Indiana Academy of Science 
metallic solution as amalgam to aqueous solution as lead nitrate, that 
is, a state of equilibrium was established, leaving part of the lead still 
in the amalgam from which it did not precipitate as the sulfate; or it 
might be due to the solubility of the lead sulfate in the excess of cop- 
per nitrate, or to a combination of the two. The method seemed to 
be useless for quantitative determinations and no further work was 
attempted with it. 
With the idea that lead might be precipitated quantitatively as 
the chromate in the presence of copper nitrate, the solution of lead 
nitrate being used as electrolyte was analyzed for its concentration of 
lead by precipitating the metal, in the presence of a few drops of 
acetic acid, with potassium dichromate.* The precipitate was dried at 
120° C. in a Gooch crucible. Then the same volume of solution of 
lead nitrate was treated as before except for the addition of 20 ec. of 
the solution of copper nitrate before the precipitation of the lead chro- 
mate. The results shown in Table IV indicate either that the solubility 
of lead chromate in a solution of copper nitrate is very small, or that 
errors are inherent in the procedure which serve to compensate such 
solubility. 
TaBLe IV. 
Solubility of Lead Chromate in a Solution of Copper Nitrate 
No. Volume of Solution Volume of Solution Weight of 
| 
of Copper Nitrate | of Lead Nitrate PbCrO, 
None 50ce 0.3316 
- . 0.3313 
0.3312 
0.3309 
0.3308 
20ce 
< | 
eR RR 
“ 
oF WN 
Determination of Lead in Lead Amalgam as Lead Chromate. Since 
there seemed to be only a small amount of lead lost when precipitated 
as the chromate, in the presence of 20 cc. of a 10 per cent solution 
of copper nitrate, the next step was to ascertain whether the lead in a 
lead amalgam could be quantitatively determined as the chromate. Fol- 
lowing the procedure used in the attempt to determine the lead as sul- 
fate up to the point of precipitating the lead, a few drops of acetic 
acid was then added, followed by a solution of potassium dichromate 
sufficient to complete the precipitation. The amalgam had been made 
TABLE V. 
Determination of Lead in Lead Amalgam as Lead Chromate 
No. Lead Taken Lead Found Difference | Percent Variation 
1 0.3153 0.3149 ¥ —0.0004 —0.12 
2 0.2616 0.2615 —0.0001 —0.04 
3 0.2763 0.2761 ‘A —) .6002 —).07 
4 0.3013 0.3014 +0.0001 +0.03 
5 0.2751 0.2754 +0.0003 +0.11 
1 Secott—Standard Methods of Chemical Analysis, p. 236 (1917). 
