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INDUSTRIAL AND ENGINEERING CHEMISTRY
high temperature. Samples pasteurized a t 196" F. (91" C.) lost their cloud when stored a t 95" ,F. (35" C.), but others pasteurized a t 199-203" F. (93-95" C.) retained their cloud almost indefinitely. These last two groups are not listed in the tables. The disappearance of cloud does not parallel the off-flavor development. Samples losing their cloud during storage a t 40" F. have retained a pleasant fruity flavor and aroma although these qualities are slightly different in those samples retaining cloud. AMINO NITROGEN.The results show no correlation between the quality of the juice and the amount of amino nitrogen; if anything, there is a slight increase in amino nitrogen content in the more mature fruit of the later packs. The suggested correlation between amino nitrogen and taste tests might be due to the normal preference of some individuals for an acid (undermature) juice in contrast to a sweet (overmature) juice.
Acknowledgment The writers are indebted to the Productive Equipment Corporation of Chicago for the vibrating screen used in the experiments. Literature Cited (1) Bailey and Fisher, J . Am. Med. Assoc., 110, 650 (1938). (2) Chace, Loesecke, yon, and Heid, U. S. Dept. Am., Circ. 577 (1940). (3) Cruess, W. V., Calif. Agr. Expt. Sta., Bull. 244, 157 (1914). (4) Davis, W. B., Am. J. Botany, 19, 101 (1932). (5) Eddy, C. W., IND.ENG.CHBM.,28, 480 (1936).
(6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20)
Vol. 33, No. 10
Evelyn, Malloy, and Rosen, J . Biol. Chem., 126, 645 (1938). Harris and Ray, Biochem. J., 27, 303 (1933). Heid, J. L., Cunner, 88, No. 25, 16-17, No. 26, 16-17 (1939). Heid and Scott, Fruit Products J., 16, 136 (1937). Ibid., 17, 100, 121 (1937). ENG.CHEM.,26, 857 (1934). Joslyn and Marsh, IND. Ibid., 27, 186 (1935). Joslyn and Marsh, Univ. Calif., Coll. Agr., C ~ T C 344 . (1937). Joslyn, Marsh, and Morgan, J. Biol. Chem., 105, 17 (1934). Loeffler, H. J., IND. EXG.CHEM.,ANAL.ED., 12, 533 (1940). Loesecke, von, Mottern, and Pulley, IND.ENG. CHEM.,20, 1302 (1928). Lorenz and Arnold, IXD. EXG.CHEM.,ANAL.ED.,10, 687 (1938). Mottern, H. H., 28th Ann. Convention, Intern. Assoc. Milk Dealers, 1935. Mottern and Loeseoke, yon, Fruit Products J.,12, 325 (1933). Mottern, Nelson, and Walker, J . Assoc. Oficial Agr. Chem., Nov., 1932, 614. Nelson and Mottern, IND. ENG. CHmf., 25, 216 (1933). Nelson, Mottern, and Eddy, Fruit Products J., 12, 231 (1933) Nolte and Loesecke, von, Food Research, 5 , 457-67 (1 940). Parks, C. T., Canner, 90, No. 12, pt. 2 , 71 (1940). Pulley and Loesecke, yon, IND. ENQ.CHEM.,31, 1275 (1939). Stevens, J. W., IND.ENG CHEM.,ANAL.ED., 10, 269 (1938). Tillmans, Hirsch, and Jaokisch, Z . Untersuch. Lebensm., 63, 241 (1932). Tressler, Joslyn, and Marsh, "Fruit and Vegetable Juices", New York, Avi Pub. Co., 1939. U. S. Citrus Products Station's Staff, U. S. Dept. Agr., Bur. Chem. Soils, Mimeographed circ., May 20, 1936. Wilson, C. P., IND. ENG.CHEM.,20, 1302 (1928).
CoarRrsuTIoN 8 from the Ag:icultu:al Chemical Research Division. Represents oollaborative work between The Glass Container Association Fellow and the Fruit and Vegetable Chemistry Laboratory, Los Angcles, Calif.
Specific Heat of Calcium Carbide at Low Temperatures IC. IC. ICELLEY Pacific Experiment Station, U. S. Bureau of Mines, Berkeley, Calif.
F
UNDAMENTAL data concerning calcium carbide are almost entirely lacking in spite of the wide industrial use of this material. The situation recently has become more acute because of the desirability of making a t least approximate thermodynamic calculations pertaining to certain proposed new uses such as the reduction of magnesium oxide by calcium carbide a t high temperatures. The lack of data probably is due to the difficulty of obtaining or preparing enough material of adequate purity. The product ordinarily available has a purity of 85 per cent or less. This paper presents specific-heat data in the temperature range 51" to 298' K. obtained with a commercial sample of cdcium carbide of 91 per cent purity, furnished by the National Carbide Corporation. The purity of this sample leaves much to be desired from the viewpoint of fundamental studies, although i t is exceptional from a commercial standpoint. However, as low-temperature specific heat and entropy data are lacking for this important substance, and as other work precludes undertaking the preparation of purer material in the near future i t appears justifiable to report the results a t hand.
The specific heat of calcium carbide was determined i n the temperature range 51' to 298' IC. The material studied had a purity of only 91.0 per cent, but i t was carefully analyzed and a correction for impurities was made. The course of the specific heat curve is normal. The entropy of calcium carbide was obtained as S,,,,, = 16.8 f 0.5. The free energy of formation of calcium carbide from calcium and graphite was calculated to be AF0z81.,6= -15,300.
Analysis of Sample From a generous sample, pieces of about 0.5 inch size were selected, the dusty outside coating was brushed off, and the material was crushed to pass a 20-mesh and be retained by a 48-mesh screen. The exclusion of finer particles improved
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1941
the quality of the sample somewhat. Analysis of the portion used in the measurements showed 91.0 per cent calcium carbide, which compares favorably with the National Carbide Corporation's prior determination of 91.3 per cent. The principal impurity was calcium oxide, of which 6.47 per cent was found. I n addition, the sample analyzed 1.15 per cent silica, 0.77 alumina, 0.20 carbon, 0.08 magnesia, 0.18 iron, and a small but undetermined amount of sulfur. For the purpose of correcting the specific heat results it was assumed that the iron and sulfur were combined as 0.29 per cent ferrous sulfide. These items account for 99.96 per cent. A 123.3-gram sample was employed in the measurements. Specific Heat
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, HEATOF CALCIUM CARBIDE TABLE I. SPECIFIC T , I(. Cp/Gram
'
C /Gram Cp/Cram 8ormula (Cor.) M ~ B B
Cp/Gram
T , K. Cp/Gram
Cp Gram Formula (Cor.) Mass
53.0 56.8 60.7 65.0 69.7 74.0
0.0378 0.0430 0.0489 0.0558 0.0633 0.0701
0.0402 0.0456 0.0516 0.0588 0.0665 0.0735
2.57 2.92 3.31 3.77 4.26 4.71
194.6 204.9 214.7 224.5 235.1 245.0
0.1938 0.1983 0.2026 0.2066 0.2104 0.2141
0.1991 0.2036 0.2078 0.2117 0.2154 0.2192
12.76 13.05 13.32 13.57 13.81 14.05
79.6 83.2 92.0 101.9 112.5 122.7
0.0787 0.0842 0.0974 0.1112 0.1249 0.1871
0.0824 0.0879 0.1016 0.1196 0.1296 0.1422
5.28 5.64 6.51 7.41 8.31 9.11
254.9 265.2 275.8 285.7 295.0
0.2170 0.2195 0.2237 0,2260 0.2272
0.2220 0.2243 0.2285 0.2309 0.2318
14.23 14.38 14.65 14.80 14.86
133.0 143.7 153.6 164.1 174.0 184.3
0.1482 0.1586 0.1662 0.1743 0.1815 0.1879
0.1534 0.1640 0.1715 0.1797 0.1867 0,1933
9.84 10.51 10.99 11.52 11.97 12.39
The mecific heat data were obtained with the apparatis described previously (9). The error in the measurements is considered to average 0.3 per cent over the temperature range studied (51" to 298" K.), no allowance being made for the error in correcting for impurities.
cent purity. Their results are mutually discordant and are low in comparison with the present figures.
Entropy The entropy increment between 50.12' and 298.16' K. was obtained graphically from a plot of Cp against log T as 15.82 units. The lower temperature results appear just on the verge of coincidence with a Debye function, D (246/T). Consequently the specific heat curve was extended smoothly into this function and extrapolated to 0' K. accordingly, The extrapolated portion of the entropy is 1.02 unit. The sum gives SzQs.le= 16.8 =t0.5. The error in this result would have been assigned the value 1 0 . 2 so far as the measurements 3 assigned t o alone are concerned, and the additional ~ 0 . is allow for errors in the analysis and correction for impurities.
Free Energy of Formation
M
200
300
T,OK.
FIQURE1. SPECIFIC HEATOF CALCIUM CARBIDE
The results, expressed in defined calories (1 calorie = 4.1833 International joules) are given in Table I. Columns 1and 5 contain the mean temperatures of the determinations. The temperature intervals range from 2.75" to 5.44' K. so that essentially true specific heats are reported. Columns 2 and 6 give the specific heat per gram as measured. Columns 3 and 7 show the specific heat per gram after correcting for impurities. Correction was made on the assumption of additivity of specific heats, employing previously compiled values (4). The magnitude of the correction ranged from 6.0 per cent at 53" to 2.0 per cent a t 295" K. Columns 4 and 8 give the specific heat per gram formula mass (64.10 grams). Figure 1 shows the latter results plotted against temperature. The course of the specific-heat curve is normal and need not be discussed. There are no previous data in the temperature range studied with which to compare the present results. Ruff and Josephy (6) obtained three mean specific heats in the range 445.6" to 645.6' K. on a sample of about 80 per
The heat of formation of calcium carbide from calcium and graphite was reported as - 14,100 calories a t room temperature by Ruff and Josephy (6). No reliance would be placed in this value except for the statement of Roth (6) that in some unpublished investigations he obtained approximately the same result. This value also was adopted by Bichowsky and Rossini (1). The entropies (4) of calcium and graphite at 298.16' K. are, respectively, 9.95 * 0.1 and 1.36 * 0.03. Consequently the entropy of formation of calcium carbide is ASas.18 = 4.1, and i t follows that the free energy of forma= -15,300. The last retion from the elements is AF'ZQ~.~B sult is of the magnitude previously calculated (3) from other considerations and is probably more reliable.
Acknowledgment The sample of calcium carbide was furnished by the National Carbide Corporation through the courtesy of F. Pruyn, Jr., under whose direction it had been selected over a period of time, presumably in the course of ordinary manufacture. Analysis of the sample was kindly made by G . W. Marks, Metallurgical Division, U. S. Bureau of Mines.
Literature Cited Bichowsky and Rossini, "Thermochemistry of Chemical Substances", p. 120, New York, Reinhold Pub. Gorp., 1936. Kelley, J. An. C h e m Soc., 63, 1137 (1941). Kelley, U.5 . Bur. Mines, Bull. 407 (1935). , ~Ibid., , 434 (1941). (5) Landolt-Bornstein, Physikalisoh-chemische Tabellen. 1st suppl.. p. 821, Berlin, Julius Springer, 1927. (6) Ruff and Josephy, 2. anorg. C h m . , 153, 17 (1926). PUELISEBD by permission of the Director, U. S. Bureau of Mines.
