Lead in Lead Amalgam 193 
many of the determinations showed considerable brownish-red material 
on the surface of the amalgam, after standing in contact with the solu- 
tion of 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 material. 
Determination of Lead in the Amalgam as Lead Sulfate. In try- 
ing out the method for displacing the lead from the amalgam by means 
of a solution of copper nitrate, the first attempt to precipitate the lead 
was with sulfuric acid. Amalgams containing known weights of lead 
stood four days in contact with 40 cc. of a 10 per cent solution of the 
copper nitrate. After decanting the resulting solution, an additional 
10 cc. portion of the copper nitrate stood on the amalgams for 30 min- 
utes. From the total, warm solution the lead was precipitated with 
dilute sulfuric acid. The weight of lead sulfate was determined by 
filtering it on a Gooch crucible, the ignition being accomplished by 
supporting the crucible in an asbestos ring placed in a larger crucible 
and heating the latter to dull redness for 15 minutes. The weight of 
lead was found to be uniformly low, as shown in Table II. 
Tasxe II. 
Determination of Lead in Lead Amalgam as Lead Sulfate. 
No. Lead Taken Lead Found Percent Loss 
1 0.5650 0.5606 0.78 
2 0.4748 0.4704 0.92 
3 0.5108 0.5058 0.98 
4 0.5024 0.4977 0.93 
Solubility of Lead Sulfate in a Solution of Copper Nitrate. Assum- 
ing that the low values for the lead found resulted from the solubility 
of the lead sulfate in the solution of copper nitrate, definite weights of 
prepared lead sulfate were allowed to stand four days in a 10 per cent 
solution of the copper nitrate. The precipitate was then filtered off 
and weighed as before. The results shown in Table III are only pre- 
liminary and more accurate determinations will be made under vary- 
ing conditions, but the increase in solubility with increase in concen- 
tration of copper nitrate is evident. 
Taste III. 
Solubility of Lead Sulfate in a Solution of Copper Nitrate 
No. Vol. of Sol. of PbSO, PbSO, Percent 
Cu(NOz)2 Taken Found Loss 
1 25ce 0.7000 0.6764 3.39 
2 50 0.7000 0.6556 6.33 
3 50 0.7000 0.6533 6.61 
Solubility of Lead Chromate in a Solution of Copper Nitrate. The 
foregoing work on the determination of the lead as lead sulfate and 
on its solubility in solutions of copper nitrate indicated that the re- 
sults might be due to a failure of the lead to change entirely from a 
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