~Effect of Varying Temperature.~--The effect of increased temperature is
to change the colour from brown to black, and to render the estimation
difficult.
1 c.c. at 15° C. showed the colour of 0.5 c.c. at 60° C.
2 " " " " 1.5 " at 60° C.
3 " " " " 5.0 " at 50° C.
~Effect of Varying Time.~--The colour becomes lighter on standing: 2
c.c. on standing 10, 20, and 40 minutes became equal in colour to 1.7
c.c.
~Effect of Acids and Ammonia.~--Two c.c. of the solution with 2 c.c. of
dilute hydrochloric acid became cloudy and equivalent to about 2.5 c.c.;
and a similar result was got with 2 c.c. of dilute sulphuric acid. With
2 c.c. of dilute ammonia the solution became somewhat darker, or equal
to 2.3 c.c.; but gave a very clear solution easy to compare.
~Determination of Lead in Commercial Zinc.~--Dissolve 0.1 gram of the
metal in 1 c.c. of dilute nitric acid evaporates till a solid separates
out, dilute to 100 c.c. with water, and take 20 c.c. for assay. A sample
treated in this way required 2.4 c.c.; this multiplied by 5 gives 12.0
c.c., equivalent to 1.2 milligram of lead, or 1.2 per cent. By
gravimetric assay the sample gave 1.10 per cent.
PRACTICAL EXERCISES.
1. Thirty grams of galena gave on dry assay 21 grams of lead; and this,
on cupellation, gave 15 milligrams of silver.
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