Stability of Wijs’ Solution in the Tropics REGINALD CHILD, Coconut Research Scheme, Lunuwilr, Ceylon NE of the advantages of Wijs’ solution has always been claimed
0
to be its stability.
Extreme exores-
Table I. Date 3-29-33 5-21-33 5-28-33 6-12-33 6-18-33
Solution 1 0.2730 0.2712 0.2705 0.2699 0.2703
Change of Factors of Wijs’ Solutions on Storing
Date 10-17-33 12- 8-33 4- 5-34 5-19-34 8- 7-34 9- 4-34 10- 4-34
Solution 2 (0.2170)’
Date 10-12-34
Solution 3 (0.2049)‘
Date 1-21-41
Solution 4 0.1987
sions are those of Lewkowitsch’ (S), 0,2088 10-23-34 0.1950 2- 3-41 0.1969 who went so far as to say that “in 0.2013 12- 6-34 0.1930 2-13-41 0.1966 0.1994 12-12-34 0.1926 2-28-41 0.1952 ordinary work a blank is not required”, 0.1938 4- 3-35 0.1862 6- 8-41 0.1890 0.1914 4-23-35 0.1841 6-16-41 0.1884 and of the Report of the Ninth Con:;$ 0.1908 5-22-35 0.1803 6-20-41 0.1879 ference of the International Union 9- 6-33 0.2658 8- 8-41 0.1845 10- 8-33 0.2631 8- 9-41 0.1845 of Pure and Applied Chemistry a t 10-10-33 0,2627 The Hague, 1928, quoted by Mitchell 3-29-33 12-8-33 .lo-23-34 1-21-41 to Fall in to Fall in to Fall in to Fall in (d), “kept in a well-closed bottle in 10-10-33 Factor 10-4-34 Factor 5-22-35 Factor 8-9-41 Factor the dark, the solution remains in good 195days o.0103 3OOdays 0.0150 210daya 0.0145 2OOdays 0.0142 condition for yean”. On the other Per day 0.000053 Per day 0.000050 Per day 0.000069 Per day 0.000071 hand, in the United States Hanus’ a Solutions not standardized. Faotor calculated from weights of iodine trichloride aad iodine used. solution is generally preferred to Wijs’, and Jamieson (8) recommends (2) Jamieson, G. S., “Vegetable Fats and Oils”, p. 343,A.C.S. Monothat Wijs’ solution, if used, should not be kept for more than graph, New York7Chemical Catalog Co., 1932. a month. (3) Lewkowitsch, J., “Chemical Technology and Analysis of Oils, Norris and Buswell ( 5 ) have recently found that over a total Fats, and Waxes”, 6th ed., Vol. I, p. 417, New York, Macperiod of 505 days, Wijs’ solution gave unvarying results for the millan Co., 1921. (4) Mitchell, C. A., “Recent Advances in Analytical Chemistry. iodine values of the same substrate. It will, it is hoped, be of inVol. I, Organic”, p. 69, London, J. & A. Churchill, 1930. terest to record the writer’s experience with this reagent in the (5) Norris, F. A., and Buswell, R. J., IND.ENQ.CHEM.,ANAL.ED.. tropical low country of Ceylon, where the mean laboratory tem16, 417 (1944). perature is approximately 81’ F. and the mean relative humidity about 84%.
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Indirect Stabilization of Ferrous Sulfate Solution
The reagent has been repared from iodine trichloride sup lied in sealed ampoules. (Oftamed from British Drug Houses, Etd., London. The weight of the contents of am oules varied considerably and as much as 11 grams has been Pound in one stated to contain 9 grams. The contents, however, were never less than stated.) The usual procedure has been to weigh the ampoule, open it, and empt the contents, washing out with acetic acid used for the solution. $he ampoule is dried and renyeighed. Sufficient iodine is then employed to form iodine monochloride with about 2% excess of iodine. The solution made up to 1 liter is standardized and adjusted to approxihately 0.2 N,. The usual precautions are taken to prevent absorption of moisture.
FREDERICK R. DUKE Frick Chemical Laboratory, Princeton University, Princeton, N. J.
A
LTHOUGH ferrous sulfate is one of the most useful reducing agents, its instability toward air oxidation makes frequent restandardization necessary. The common practice of storing the solution under hydrogen is objectionable because of the explosive nature of the gas. The method for indirect stabilization described here depends upon reduction of any ferric iron in the solution as it emerges from the stock bottle, using a lead a m a l g a m reductor. Lead easily reduces iron, but has no tendency to reduce hyK drogen ion, thereby eliminating gas formation; in addition, the lead sulfate Figure 1. Apparatus formed in the reductor is A. Fine ~ I r u cotton (Pyrex 790) insoluble and remains in E . Amrlgrm the reductor. The net reC. Cwrm cllatr cotton sult is the addition of nothing t o the solution, the removal of a small amount of sulfate ion, and completely reduced ferrous sulfate a t all times. AMALGAM. One kilogram of approximately 20-mesh lead metal is stirred with 30 ml. of pure mercury. After thorough mixing, the amalgam is washed with 1M sulfuric acid. APPARATUS.A 30-cm. (12-inch) Kimble calcium chloride tower (catalog No. 19,500) is equipped as shown in Figure 1, with stoppers, the amalgam, and glass wool. The large size of the tower permits rapid flow without pressure, complete reduction, and long life. When the amalgam becomes well filled with lead sulfate, it should be removed from the tower and washed with water until substantially free of the sulfate. The ferrous sulfate solution should be no less than 1M in sulfuric acid for rapid and complete reduction.
Table I gives a selection from laboratory records of the periodiid standardization of such solutions. This has been done in the usual way by adding potassium iodide and titrating with 0.1 N sodium thiosulfate solution, the latter having been standardized in each case against weighed quantities of potassium dichromate,
A.R. Wijs’ solutions 1 t o 4 were, during the stated periods, in fairly regular use, and when not actually in use, were kept in the dark in amber-colored ground-glass stoppered bottles. That the loss in strength is partly due to small access of water vapor during actual use, when the stopper is removed from timeto time, is not unlikely (cf. Hilditch, I ) , but when the figures in Table I are plotted it is observed that the drop in titer during a period of nonuse is of the usual order. In general the drop in factor has been reasonably regular a t approximately 0.00006 N per day-that is, the solution during normal use loses about 1% of its strength in a month. Iodine values determined on the same samples of oils using a fresh solution side by side with one 10 months old gave concordant results and the writer is of opinion that there is no risk in keeping a solution in use for that length of time, if blanks are run eacb time i t is used. This is usual, and clearly was the practice of Norris and Buswell, whose results do not indicate how far the absolute titer of their Wijs’ solution changed during use. LITERATURE CITED
(1) Hilditch, T. P.,“Industrial Chemistry of Fats and Waxes”, p. 41, London, BailliBre Tindall & Cox, 1927.
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