ANALYTICAL EDITION
July 15, 1941
455
authors have applied the combination of oxygen bomb combustion and benzidine sulfate titration to the problem of determining the residual methionine present in a highly purified sample of natural leucine.
few hundredths of 1 per cent of sulfur present in a n organic substance is described.
The procedure was as described above, n-ith a few modifications. The bomb washings were evaporated to dryness on the steam bath after they had been filtered following the addition of ammonia. The evaporation residue was then redissolved in 20 cc. of water and benzidine sulfate was precipitated after proper acidification. Further, in order to ensure completeness of crystallization of benzidine sulfate even near its solubility borderline the precipitate was filtered only after it had stood overnight at about 0" C. Finally, each determination was accompanied by an exactly corresponding blank determination.
Baernstein, H. D., J . Biol. Chem., 106, 451 (1934). Blix, G., Z . physiol. Chem., 178, 109 (1928). Fiske, C. H., J . Bid. Chem., 47, 59 (1921). Garelli, F., and Saladini, G.. Atti acad. sci. Torino, 66, 6, 163 (1931). ( 5 ) Kassell, B., and Brand, E., J . B i d . Chem., 125, 145 (1938). (6) Lavine, T . F.,Ibid., 113, 583 (1936). (7) Letonoff, T . V., and Reinhold, J. G., Ibid., 114, 149 (1936). (8) Lugg, J. W.H., Biochem. J., 32, 2114 (1935). (9) Masters, M., I b i d . , 33, 1313 (1939). (10) Mueller, J. H., Science, 81, 50 (1935). (11) Owen, E. C., Biochem. J., 30, 352 (1936). (12) Parr Instrument Co., Moline, Ill., Booklet 114. (13) Pirie, N. W., Biochem. J., 26, 2044 (1932). (14) Toennies, G., Grouth, 1, 337 (1937). (15) Toennies, G., J. Bid. Chem., 122, 27 (1937). (16) Toennies, G., and Bennett, AI. A., J . Bid. Chem., 112, 39 (1935). (17) Toennies, G., and Kolh, J. J.,Ibid., 126, 367 (1938). (18) Toennies, G., and Lavine, T . F., Ibid., 89, 153 (1930). (19) Ibid., 113, 571 (1936). (20) Zahnd, H., and Clarke, H. T., J . Am. C'hem.SOC.,52,32775 (1930).
Table IT shows that with these precautions small amounts of sulfate are determined with a n accuracy equal to the analytical precision and that amounts of the order of magnitude of the reagent blank may escape determination when insufficient time is permitted for crystallization. Finally, complete determinations Tyere run on the reagents only, as well as on a sample of synthetic leucine (dL-). The identical values of the two pairs of determination show t h a t the synthetic product is, as mould be expected, free of sulfur. The magnitude of the blank values is notevorthy. Systematic experiments in which one component was varied a t a time showed that the various components are responsible approximately as follows: 1 cc. of Decalin, 0.00 cc. (0.05 S sodium hydroxide); 25 mg. of ammonium nitrate, 0.12 cc.; 200 cc. of water, 0.02 cc.; and 4 cc. of benzidine hydrochloride solution, 0.01 cc. Careful control of the amount of ammonium nitrate added as oxidation catalyst and use of the purest grade available are advisable because of its large contribution to the blank value and because erratic values and evidence of incomplete combustion were encountered when excessive amounts (more than 100 mg.) mere used. The role of the blank value in the benzidine determinations of the preceding .ections is greatly diminished b y the fact that not more than 8 per cent of the total bomb washings were employed there. For the next pair of determinations synthetic mixtures of dl-leucine and dl-methionine were prepared by adding 0.400-cc. portions of a solution of 120 mg. of dl-methionine in a volume of 50 cc. to quartz crucibles containing the 700-mg. samples of dl-leucine; after mixing with a piece of fuse wire the crucible and contents were dried overnight a t 100". The results show that the added methionine sulfur, corresponding to a 0.03 per cent sulfur contamination, is recovered with a n accuracy of about 96 * 3 per cent. The final pair of determinations shows the results obtained on the natural leucine. Calculation yields the figures 0.0180 and 0.0166 per cent for the sulfur content. A conservatire evaluation of these results and the control and blank determinations seems to justify the statement t h a t the leucine in question contains 0.017 * 0.002 per cent of sulfur.
Literature Cited (1) (2) (3) (4)
by a grant from the Leffmann Fund of the Wagner Free Institute of Science.
AIDED
Simple Condenser for Use during Digestion Operations RAYBIOSD SZY3IANOWITZ Research Laboratories, Acheson Colloids Corp., Newark, N. J.
W
HEX i t is necessary to employ beakers for longtime digestions, a simple condenser of the type described below presents several advantages over the watch glass conventionally used as a cover. I n the first place, evaporation is practically eliminated-a rather important factor when espensive reagents, such as 30 per cent hydrogen peroxide, are involved. Furthermore, where a mixture of reagents is used, their initial ratio is well maintained despite any wide difference which may exist between their boiling points. One who has had occasion to digest solids in a mixture of nitric and sulfuric acids for extended periods will appreciate the difficulty in keeping reasonably constant the composition of such a mixture. The condenser in question is nothing more than a round-bottomed, short-necked, Pyrex flask carrying a
Summary
il convenient procedure for the oxitlation of organic sulfur compounds, preparatory to sulfur determination, by alkaline permanganate is described. S o sulfate is formed froin methionine by this procedure. Incomplete and variable oxidation of met.hionine sulfur is shown to occur in some other \vetoxidabion methods. A t'ested procedure for the determination of sulfur in organic compounds is described in which the substance is burned in a bomb b y compressed oxygen and t.he sulfate formed is determined acidimetrically as benzidine sulfate. The presence of sodium chloride and mercury salts is shown within certain limit's not to interfere in this method. Its successful application t'o the accurate determination of a
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two-hole rubber stopper fitted with two pieces of glass tubing bent a t right angles. One serves as an intake and the other as an outlet for water. I t is desirable that the intake tube be extended to a point close to the bottom of the flask. This improvised condenser may be of any convenient diameter, dependent, upon the size of the beaker with which it i3 to be employed. The apparatus depicted may, of course, be employed RS R single unit or in series.
