Effect of Soft Glass on Melting Point of Rotenone HOWARD A. JONES Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, Washington, D. C.
J
ONES and Wood ( I ) have recently shown that the melting point of a-toxicarol is markedly lower in soft-
dealing with rotenone and related compou;ds, melting points determined by capillary tube should be made in a glass of glass than in hard-glass capillary tubes; one sample that low alkalinity such as Pyrex. melted at 230-231" C. in Pyrex melted a t 205-206" C. in It is not intended to imply that the melting-point method of determining rotenone purity is used or recommended by this ordinary soft glass. The effect was shown to be due to the writer. He merely wishes to point out to those who employ it that use of soft glass for melting point constitutes a O F PURITY O F ROTENONE IN C.4PILLARY TABLE I. MELTINGPOINTS AND DEGREES GLASSTUBES possible source of error. As a matter Of fact it is his 'pinion that Other In Ordinary Soft Glass I n Pyrex Glass I n Corning Electrode Glass Rotenone Melting Degree of Melting Degree of Melting Degree of sources of error are also present in this Sample point purity point purity point purity method and that purity of rotenone C. (cor.) % c. (cor.) % c. (cor.) % 155-156 98.6 may be more accurately determined Pure 163-164 100 159.5-160.5 99.4 Impure by other means. sampie A 161-162 99.8 157.5-159 99.0 154.5-155.5 98.4 O
Impure sampie B
151.5-153.5
97.8
149-151
97.2
146.5-148.5
Literature Cited
96.6
(1) Jones. H. A.. a n d Wood. J. W.. J. Am. Chem. Soc., 63, 1760-1 (1941).
(2) Koolhaas, D. R.,Bull. Buztenzorg jardin botan., [3]12, 563-74 (1932). EXQ.CHEM.,ANAL.ED., (3) Meijer. T.M., a n d Koolhaas, D. R., IND. 12,205-9 (1940).
greater alkalinity of the soft glass. Rotenone has also been found to exhibit a less marked but definite depression of melting point in soft glass. Pure rotenone melted about 3" lower in ordinary soft glass than in Pyrex and about 5" lower in a more alkaline soft glass (Corning electrode glass No. 015) than in ordinary soft glass. This effect is important in the analysis of derris and cube roots for their rotenone content. Many workers use the melting point as a qualitative indication of the purity of the rotenone obtained. Furthermore, in the quantitative method of Meijer and Koolhaas (3) the melting point of the separated rotenone is used as one means of calculating the purity, and from this the content, of the sample. The melting points of pure rotenone and of two samples of impure rotenone in Pyrex and in two soft glasses are given in Table I. The glass was cleaned, and melting points were determined by the methods used in the work on a-toxicarol (1). From the qualitative standpoint a melting point of 155156", the value obtained for pure rotenone in Corning electrode glass, would not be considered to indicate a high degree of purity. Furthermore, the melting points in soft glass are not only lower but less sharp than in Pyrex and thus give every indication of material of lower purity. By use of a graph given by Koolhaas @), the degree of purity indicated by these melting points was determined, on the assumption that the graph held for the samples used here, and these values are also recorded in Table I. Meijer and Koolhaas (3) state that for calculation of purity by this method the melting point should not be less than 140"; hence, samples with lower values have not been included in this work. The maximum difference in apparent purity of any one sample as calculated from the melting points in Pyrex and Corning electrode glass is shown to be 1.4 per cent. This would introduce an error of only about 0.1 per cent in the rotenone content of a 5 per cent rotenone sample and about 0.2 per cent in that of a 10 per cent sample. Although the discrepancy in melting point between Pyrex and soft glass does not introduce a very serious error into results by this method of calculation, it is a recognized source of error which is easily eliminated and should be avoided. To specify that all melting points should be taken in the same type of soft glass is not sufficient, since the lowering effect, as stated for a-toxicarol, must depend on the degree of contact with the glass, and hence on the size of the crystals and other factors. In all analytical and investigative work
Stabilitv of the PermanaanatePeriodate Color SysFem J. P. MEHLIG Oregon State College, Corvallis, Ore.
I
N MAKIKG a spectrophotometric study of the Willard
and Greathouse periodate method (a) for the colorimetric determination of manganese the writer (1) found no evidence whatever of fading or other change in the color of the system over a period of two months. The solutions which had been used in this test, containing 1.25, 2.50, 3.75, and 5.0 mg. of manganese with 10 ml. of concentrated sulfuric acid and 0.3 gram of potassium periodate er 250 ml., were allowed t o stand in glass-stoppered Pyrex bot& in diffuse light for an additional 23 months. Spectral transmission curve0
were then made and compared with the curve6 given by the corresponding freshly prepared solutions. From the transmittancy at 522 mp the percentage error in the apparent concentration of manganese was calculated ( 1 ) by use of the special color slide rule. TABLEI. STABILITY OF COLOR Concentration of Manganese Mdl. 5 10 15 20
Transmittancy a t 522 mp Old Fresh solution solution
% 39.5 15.2 5.9 2.0
% 39.8 16.6 6.0 2.7
Apparent Change in Concentration of Manganese
% -0.7 -4.6 -0.5 -7.5
The results, given in Table I,.prove that the color of the permanganate-periodate system is exceptionally stable.
Literature Cited (1) Mehlin. J. P..IND. ENQ.CHBM..ANAL. ED..11. 274 (1939). (2j Willarz, H. H..and Greathouse, L. H., J. Am; Chem. Soc., 39, 2366 (1917).
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