USE OF POTASSIUM FERROCYANIDE AS A CONFIRMATORY TEST FOR ZINC J. P. MEHLIO, OREGONSTATE AGRICULTURAL COLLEGE, CORVALLIS, OREGON
As the usual confirmatory test for zinc-the green incrustation formed by fusion with cobaltous nitrate-has never given my students very satisfactory results, I tried out the ferrocyanide test in my qualitative classes last fall. The test was adapted from the procedure used in the volumetric determination of zinc by the ferrocyanide method and is as follows: Dissolve the supposed zinc sulfide precipitate in 5 cc. G N HCl. Boil to remove H2S. Just neutralize with ammonium hydroxide and add 3 cc. concentrated HCI. Heat nearly to boiling and add 5 cc. 1 N K4Fe(CN)s solution. White precipitate of zinc ferrocyanide, becoming flocculent on addition of excess reagent, shows presence of zinc. Tabulated student results are given in the following table. Year
1926 (new test) 1925 (old test) 1924 (old test) 1923 (old test) Total (old test)
Time$ zn reported
Times Z"
correctly
mlrsen
52 41 19 14 74
6 6 6 3 15
%
correct
89.6 88.1 76.0 82.4 83.1
-
The ferrocyanide test thus shows a marked improvement in results over the former test and warrants further use.
