1668
NOTES
hydrogen peroxide. The darkening of this form of zinc sulfide in the light is reversible in the dark. The second explanation is consistent with the observation that the stoichiometric relationships among the products, in the case of cadmium sulfide in Table IV, remain fairly constant over an extended period of time. If the oxidation of sulfide were effected principally by the hydrogen peroxide one would expect an acceleration of the appearance of sulfate ion with time as the hydrogen peroxide concentration increases in the solution. Further work on the stoichiometry of the oxygen uptake is now in progress in our laboratories, to help decide the correct interpretation of these surface oxidations of photoconducting sulfides. HEATS OF COMBUSTION. VI. THE HEATS OF COMBUSTION OF SOME AMINO ACIDS BY TOSHIO TSUZUEI A N D HERSCHEL HUNT Department of Chemistry and Purdus Research Foundation, Purdue University, Lafayette, Indiana Received June $4, 1967
The heats of combustion of L-glutamine, L-glutamic acid, L-valine and L-leucine, have been determined by means of a non-adiabatic calorimeter. The method is essentially the same as that described by previous workers in this except that thermistors are used as temperature-sensing elements rather than thermocouples.
Vol. 61 TABLE I NITROQENCONTENTS OF AMINOACID SAMPLES Amino acid
GGlutamine >Glutamic acid >Valine >Leucine
Nitrogen content. % Theor. Found
19.17 9.52 11.96 10.68
19.01 9.56 12.13 10.63
The heats of combustion of the amino acids at constant volume and a t 25" for the reaction producing gaseous carbon dioxide, liquid water and gaseous nitrogen, are given in Table 11. The standard deviations were calculated in accordance with recommendations by Rossini and Deminglband the atomic weights used in the computations are those of the 1953 revision: 0 = 16, C = 12.011, H = 1.0080, N = 14.008. TABLE I1 HEATS OF COMBUSTION OF AMINOACIDS Amino acid
>Glutamine (s), C~HIOO~NS LGlutamic acid (s), C5Ho04N L-Valine (s), CsHnOJV' >Leucine (s), CaHlaOzN
Heat of oombustion, kcal./mole
614.80 & 0.15 537.01 f .I8 697.93 & .I3 853.08 f .06
The heat of combustion of glutamic acid was previously reported by Fischer and Wrede,6 by Emery and Benedict,' and by Huffman, Ellis and Wredeg determined the heat of combustion of valine. The heat of combustion of leucine was determined by Stohmann and Langbeinlo and by Fischer and Wrede.6 The authors wish to express their appreciation t o National Science Foundation for sponsoring thls research and to Drs. J. W. Amy and P. R. Marshall for their work in the major part of the apparatus modification.
The apparatus, which is described elsewhere*l4has been modified so that two thermistors (Western Electric Type 14B, 2240 and 2225 ohms at room tem erature) with a 60turn 500-ohm Resomax otentiometer (%ink Aviation Company, Model 400) and a%rown null indicator (MinneapolisHoneywell Company Model 104-WIG) in a Wheatstone bridge circuit can be used to measure the temperatures of the calorimeter and of the jacket, respectively. The thermistors were calibrated against a platinum resistance thermometer, which had been calibrated previously, and it was possible to estimate the temperature reading to less than (5) F. D. Rossini and W. E. Deming, J . Wash. Acad. Sci., 29, 416 0.0002 O . The calorimeter was calibrated with National Bureau of (1939). (6) E. Fischer and F. Wrede, Akad. Wiss. B e d . Sitzungsber., 687 Standards benzoic acid, Standard Sample 398;. I n order to promote ignition of the amino acid samples a small pellet of (1904). (7) A. G . Emery and F. G. Benedict, A m . J . Physiol., 28,301 (1911). the standard benzoic acid was placed in the stainless steel (8) H. M. Huffman, E. L. Ellis and 8. W. Fox, J . A m . Chsm. Soc., combustion capsule at an angle against one edge of the amino acid pellet. The weights of the amino acid sample 58, 1728 (1936). (9) F. Wrede. 2. physik. Chem., 76, 81 (1910). and of the benzoic acid were adjusted so that the amount (10) F. Stohmann and H. Langbein, J . prakt. Chem., [Z] 44, 383 of heat liberated would be comparable to the amount liberated in the calibration experiments. Exactly 1.1 ml. of (1891). water was placed in a Parr double-valved oxygen bomb of 0.358-1. capacity and the bomb was fdled with Linde U.S.P. oxygen to a pressure of 30 atm. absolute at 25". REACTION TIME DISTRIBUTION I N Proper corrections were made for the heat of stirring, the LAMINAR FLOW KINETIC heat exchanged between the calorimeter and the jacket, the ignition energy, and for the heat of formation of nitric acid. MEASUREMENTS The calorimeter system with 2800 g. of water had a water BYKENNETH A. WILDE equivalent of 3285 g., and the heat evolved in each determination was corrected to the value which would have been Rohm and Haas Company, Redslons Arsenal Resparch Division, liberated in a system of exactly that water equivalent. HunlsvtEEe, Alabama All the samples of amino acids were prepared by Dr. Receiced Mail 87, 1967 J. P. Greenstein of National Cancer Institute, Bethesda, Maryland, and they were said to be better than 99.9% pure. Since the Reynolds number in laboratory flow Each of the these amino acid samples was recrystallized once from water and ethanol, followed by complete drying in Z ~ ~ C U Osystems is usually well in the laminar range, one in 100" (50" for L-glutamic acid). Nitrogen contents of would expect to obtain the usual parabolic velocity the recrystallized samples were determined by the micro- profile across a circular cross-section. This profile Kjeldahl method and compared with the theoretical values \vi11 obviously result in a pronounced spreading of as shown in Table I. (1) A. J. Miller and H. Hunt, THIS JOURNAL, 49, 20 (1945). (2) M. V. Sullivan and H. Hunt, ibid., 68, 497 (1949). (3) G.M. Kibler and H. Hunt, ibid., 68, 955 (1949). (4) C. B. M i l a and € Hunt, I . ibid , 45, 1846 (1941).
reaction times, but the effect seems to have escaped attention by workers in the field. Bosworthl has calculated a distribution function for reaction times (1) R, C . L. Boaworth, Phil. Mag., 89, 847 (1948).
