INDUSTRIAL A N D ENGINEERING CHEMISTRY
382
Vol. 15. No. 4
Vapor Pressures of Carbazol, Observed and Calculatedi3z By C. E. Senseman and 0. A. Nelson COLOR LABORATORY, BUREAU OP CHEMISTRY, WASHINGTON, D. C.
A table of aapor pressures for carbazol between the temperatures N a former paper by the Using this purest sample authors3 was given a 250' and 355" C. has been given. four analyses were made The boiling point of carbazol has been determined and found to be resume of the literature for nitrogen. An average 354.76' C. instead of 351.5" C., as giaen in the literature. on vapor-pressure methods result of 8.22 per cent was Interpolation formulas haue been derived for vapor pressures and obtained. The calculated and a detailed description of the static method and latent heat of aaporization. per cent of nitrogen presapparatus used, in making ent in carbazol is 8.38. vapor-pressure determinaThis material was theretions on naphthalene, anthracene, phenanthrene, and fore accepted as pure and was used for the vapor-pressure anthraquinone. determinations. The pressures observed during three exThe work done on carbazol as reported in this paper con- perimental runs are tabulated with their corresponding temsisted of (1) purifying the compound, and (2) determining peratures in consecutive order in Table I. Using these rethe vapor pressures a t brief temperature intervals from sults, a curve was drawn and readings taken from it a t 5 slightly above the melting point to a few degrees above the degree temperature intervals. These readings are recorded boiling point, using the same apparatus as described in the in Table I1 and represent the interpolated values obtained previous paper. from the curve. In the purification of carbazol, a mixture containing 82 Since no data on the vapor pressures of carbazol over the per cent of this compound was used as a starting material. range of temperature covered in these tables seem to be I n order to remove the anthracene, phenanthrene, and other available, the authors have no way of comparing these reimpurities, this material was washed three times with ben- sults with those of other investigators. It should, however, zene at 50" C., each time keeping the mixture well agitated for be pointed out that the literature gives the boiling point of car30 min. or more. After the third washing the residue was bazol as 351.5' C. The samples the authors worked with all dissolved in boiling benzene, the solution was cooled to room failed to show a pressure of 760 mm. until the temperature of temperature, and the crystalline material filtered off and dried. 354.76' C. was reached. A melting point of 243" C. was obtained. The material of An interpolation formula that will fit these values may readthis melting point was then recrystallized from toluene. ily be derived from the Clapeyron equation of state-likewise These well-dried crystals melted a t 244.8' C. Three more an expression for the latent heat of vaporization. recrystallizations from toluene did not change this melting The relation between pressure, temperature, and latent heat point.4 of vaporization may be expressed by the equation
I
Temp. 0
c.
252.61 258.28 259.43 261.99 266.13 270.15 274.34 276.31 281.93 %88.02 290.09 291 25 292.65 294.40 298.16 302.71 307.18
Temp. 0
c.
250 255 260 265 270 275 280 285 290 295 300
TABLE I B.P., 354.76' C .
Vapor Pressure Mm. 70 .,l 82.9 85.3 92.8 103.4 114.9 128.6 135.2 156.6 181.0 191.0 197.2 202.2 212.8 231.5 260.6 286.5
Temp. O
c.
309.85 310.81 311.73 315.77 320.85 322.80 326.60 332.65 343.42 348.05 348.26 350.05 354.28 354.49 354.72 357.31 357.71
TABLEIT B. P . , 354.76' C. Vapor Pressure Temp. Mm. C. 305 65.0 310 75.9 315 87.9 320 101.1 325 115.7 330 131.9 335 149.7 340 169.4 345 191.2 350 215.3 355 242.0
Vapor Pressure Mm. 303.7 307.6 317.8 348.4 385.5 401.2 436.6 491.2 610.9 67 62 9 .. 1 4 6 693.0 753.4 759.4
K7 9 7. .38
P
dP where 7denotes change of pressure with temperature, dr L is the molar heat of vaporization, T, absolute temperature, and R, the gas constant, 1.9885. Integrating this equation between limits we get I n P2 = - L- - 11 (2) Pi R TI Tz Changing over to log,, and solving for I,, Equation 2 becomes
807.2
Vapor Pressure Mm. 271.4 303.8 339.4 378.5 421.1. 467.7 518.2 573.0 632.1 695.8 763.9
1 Presented before the Division of Dye Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 t o 8, 1922. 1 Published as Contribution No. 65 from the Color Laboratory, Bureau of Chemistry, Washington, D. C. 8 THIS JOURNAL, 14 (1922). 58. 4 Since this paper was written occasion arose for the purification of more carbazol. The method used was the same except that three crystallizations were made and all from benzene. The melting point obtained was the same as that recorded above.
(3)
by which we are enabled to determine the change in L with temperature and pressure. The values for L were calculated for a number of temperatures and pressures, and plotted on coordinate paper. Over the range of temperature investigated the curve for L was a straight line expressed by the equation L = 22799
- 13.0 T
(4)
Substituting this value for L in Equation 1 and integrating, we obtain 22799 -RT
- -1 3R. 0
+
which, when changedlover into log,, by dividing by 2.303, becomes log
9
=
24.2313
- 4670.3 T
5.0288 log T
INDUSTRIAL A N D ENGINBERING CHEMISTRY
April, 1923
This equation will give results for p that are in good agreement, with the observed values, as the following table will show: Temp. e c .
260 280
300 320
--PRESSITRE-Calcd. Obs. Mm. Mm. 87.9 88.0
149.7 242.0 378.5
150.1 242 4 380.5
Temp.
c.
340 380 355
...
--PRESSURE-Obs. Calcd. Mm. Mm.
573.0 695.8 763.9
.....
573.0 694.3 764.1
.....
383
I n order to determine whether this compound behaves as a normal liquid, the entropy of vaporization was calculated a t about 260” C. where the concentration of the vapor is 0.00507 mol per liter (approx.).6 This result gave 14.9 against about 13.7, the average obtained by Hildebrand for about 15 liquids. From this observation it seems a bit questionable whether carbazol ought to be considered as a normal liquid. 6
J . A m . Chem. SOC.,37 (1915),970.
The Analytical Detection of Rancidity’ By Robert H. Kerr and D. G. Sorber BUREAUO F ANIMALINDUSTRY, WASHINGTON, D. C.
W
The only sound basis for the anafytical detection of rancidity is an matelY 7 Per cent during HEN a rancid fat accurate knowledge of the nature of rancidity, its cause, and the chemone Year’s exposure. The is examined,the variation in the iodine numfirst Points which ical changes incident to its development. Unless applied i n the light ber is insufficient for the attract attention are the of accurate knowledge, analytical tesls are apt to be misleading. characteristic odor and Rancidity may be defined as a characteristic, spontaneous change recognition of rancidity. t a st e. When well dewhich takes place in fats. This definition is not wholly satisfactory, The heat of combustion as it includes certain conditions which are commonly called randecreases and the specific VeloPed and not obm.md gravity and viscosity inby odors and flavors due cidity but are not in fact true rancidity. A notable example is the to other Causes, they afford so-called rancidity of butter. Investigation has shown that this, crease. These changes are in most cases at least, is really a decomposition of the milk proteids not of analytical Value. a sufficient means of recogAfter the fat has become nition and further tests are present, with or without accompanying hydrolysis of the fat. The rancidity of pure, dry fats is of a digevent nature and is the result of badly rancid there is 811 not needed. In case of fats increase in the SaPonificaoriginally of good quality a different series of changes. For the purposes of this paper, the term “rancidity” will be used only in reference to changes in the fat itseu, tion number due to the and which have not aband not at any time to alterations in any substance with which the formation of acids of lower sorbed extraneous odors and molecular weight than those there is but little, if the fat is mingled, or to hydrolysis. any, need of analytical occurring in the original fat. tests, but it is not always The percentage of unsaponifiable matter increases. In such fats which are sent to the laboratory for judgment. Rancidity is often only one of several factors which must be moderately rancid fats the increased amount of unsaponiconsidered in deciding whether or not a fat is fit or unfit for fiable matter may interfere with the detection of phytosterol by methods dependent upon saponification of the fat and food. extraction of the unsaponifiable matter. CHARACTERISTICS OF RANCIDITY CAUSESOF RANCIDITY While changes in the ordinary characteristics are without As the ordinary characteristics cannot be depended upon value in detecting rancidity, they are of some interest and for the detection of rancidity it is necessary to resort to spewill be briefly considered. Changes in the free acid are of particular interest. It cial tests. Before considering these, however, it is desirable was formerly supposed that rancid and acid fats were identi- to examine into the causes of rancidity and the character cal, but it is now known that these conditions bear no rela- of the changes involved. It is now common knowledge that tion to each other. Determination of free acid is, therefore, rancidity is due t o spontaneous oxidation. While its develwithout value for the recognition of rancidity. The changes opment is influenced by several factors, it is due wholly to in the percentage of free acid during the development of ran- oxidation and can occur only in the presence of oxygen. cidity are, however, of interest. If a clear, sweet fat is The relation between oxygen and rancidity has been noted allowed to develop rancidity and the free acid is determined a t by numerous observers and has been clearly pointed out by regular intervals, it will be noted that during the first few the author.2 The exact nature of the changes involved, weeks the precentage of free acid remains stationary, or per- their origin, and the character of the products formed are haps shows a slight increase. Then a sudden drop is noted, less clearly known. It is possible a t the present time, howthe percentage of free acid falling off 0.2 to 0.4, or even more. ever, to formulate an hypothesis which appears to be in acCoincidently the physical signs of rancidity begin to appear. cord with the facts and in harmony with accepted theories Following this reduction in the percentage of free acid there of organic chemistry. This hypothesis is originally due to begins an increase in acidity. I n one particular instance, an Vintilesco and Popesco,8 who observed that fats of good acidity of 0.45 per cent a t the beginning of the experiment quality when exposed to light and air become rancid without dropped t o 0.23 per cent and then rose to 3.05 per cent after increase of acidity. This fact led them to assume that fats are able to fix oxygen from the air without previous hydrolone year’s exposure. The iodine number suffers a reduction. I n one set of ysis. It seemed to Vintilesco and Popesco that the oxygen fats the reduction varied from approximately 4 to approxi- ought to be easily displaced from such fats by readily oxidizable substances, particularly in connection with peroxi1 Presented before the Division of Agricultural and Food Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 t o 8,1922.
(Isle), 471;
2
Rerr, THISJOURNAL, 10
8
f. pharm. chim., 12 (1915),318.
Cotton Oil Press, 6 (1921),35.
