1 " 9.9 " 20.0 " 50.0 " 100.0 "
~Determination of Arsenic in Metallic Copper.~--Put 1 gram of the copper
filings, freed from particles of the file with a magnet, into a
16-oz.-flask; and distil with the ferric chloride mixture, as above
described. Neutralise the distillate; acidify; add bicarbonate of soda
and starch; dilute; and titrate with the standard solution of
iodine.[107] Make a blank determination with 1 gram of electrotype
copper, proceeding exactly as with the assay; and deduct the amount of
arsenic found in this experiment from that previously obtained.
Working in this way on a copper containing 0.38 per cent. of arsenic and
0.80 per cent. of antimony, 0.38 per cent. of arsenic was found.
~Determination of White Arsenic in Crude Arsenic.~--Weigh out 1 gram of
the dried and powdered substance (or 0.5 gram if rich), and digest with
10 c.c. of a 10 per cent. solution of soda; dilute to about 50 c.c., and
filter. Render faintly acid with hydrochloric acid, and filter (if
necessary); add 2 or 3 grams of bicarbonate of soda in solution, then 5
c.c. of starch, and titrate the cold solution with the standard solution
of iodine.
The following is an example:--
1 gram of crude arsenic required 53.7 c.c. "Iodine;"
100 c.c. "Iodine" = 0.6000 gram white arsenic;
100 : 53.
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