HEATS
OF COMBUSTION.
HEATS OF COMBUSTION.
The Heats MILES
of
Combustion
V. SVLI.IYAN
of and
Department of Chemistrij, Purdue
497
IV
IX'1
Five Aromatic HEHSUHEL
Amines
HUNT
nirersil//, laifai/ette, Indiana
Received Rebruari/ 20, 1948
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The heats of combustion have been determined for five aromatic amines, using the same ordinary or non-adiabatic calorimeter described by Miles and Hunt (2) and modified by Miller and Hunt (3). As a supplement to the schematic drawing published in the former paper (2), an “exploded” view of the bomb, calorimeter, and jacket is shown in figure 1. In addition to the corrections described by Miller and Hunt (3), a method was devised for estimating the electrical energy involved in each combustion rather than assuming an average value. This was accomplished by inserting a fastacting relay in the ignition circuit and operating an electric stopwatch (Standard Electric Time Company, Type S-10) through the relay. Using a 10-cm. length of ignition wire supplied by the Parr Instrument Company, and a 14-v., BO-cyele source of power, we found that a current of about 3 amp. was required to fuse the wire and ignite the sample. Individual fusion times ranged from 0.1 sec. to XXTen combined with the energy 2.0 sec. with an average value of 0.5 sec. liberated by the burning of the wire in each determination, this variation corresponded to about ± 0.1 per cent of the total observed temperature rise, and represents a necessary correction when one is trying to obtain a precision of 0.01 per cent.
In making the temperature measurements, galvanometer deflections were observed through a telescope. A sensitivity of about 0.3 microvolts per millimeter was obtained by using an optical lever of 2 meters. XXTiite (5) recommends a precision of 0.4 sec. in timing these observations when 0.01 per cent over-all precision is desired. This was accomplished by the use of an audible -min. interval timer, consisting of a photoelectric relay operated from the sweep second land of an accurate stopwatch (see figure 2). The image of a 2.5-v. flashlight bulb was thrown onto the watch face by a lens. The image was returned lens by a small mirror (a silvered piece of microscope coverglass) o the same A portion of the returning beam was reflected by a clear in the watch face. to a ‘overglass photoelectric cell. The photoelectric cell triggered a relay ciruit which included an OA4G cold-cathode tube, and the relay put a (i-v. ignal into a speaker to give a sharp click each time the hand of the watch cut the of light. The flashlight bulb was operated at about two-thirds of its )eam ated voltage to help extend its life. Samples were prepared in the form of cylindrical pellets weighing approxi1
This article is based upon a thesis submitted by Miles V. Sullivan to the Faculty of the Iraduate School of Purdue University in partial fulfillment of the requirements for the .egree of Doctor of Philosophy, June, 1948. 1
Fig.
1.
Exploded view of the calorimeter system
Fig. 2. Internal view of the interval timer. 1. stopwatch: 2. lens; 3. partially reflecting surface; 4, light source; 5. photoelectric cell; (i, electronic trigger tube; 7. power relay; S, transformer. 49 N
HEATS OF COMBUSTION.
499
IV
mately 1 g. each. The exact weight of each sample was adjusted so that 10.0 ±0.2 kcal. of heat would be liberated in a system whose water equivalent was about 3100 g. The sample was placed in a previously ignited stainless-steel crucible in a double-valved Parr oxygen bomb which has a volume of 358 ml. One milliliter of water was added, and the bomb was filled to 30 atm. absolute pressure with oxygen. Temperature measurements were made with a nine-junction copper-constantan thermel and a White double potentiometer. Observations began with a 20-min. rating period, followed by ignition of the sample and a 20-min. “X” period. A second 20-min. rating period concluded the temperature observations. The equipment was standardized with National Bureau of Standards benzoic acid sample 39f.
In this
manner
the following heats of combustion AMINE
were
obtained:
HEAT OF COMBUSTION
kcal.¡mole
8-HydroxyquinoIine...........................
5-Xitro-y-toluidine...........................
3-Xitro-p-toluidine............................ /j-Aminoacetophenone......................... Ethyl /j-aminobenzoate........................
1064.9 910.44 915.12 1129.7 1122.1
±0.2 ± 0.30 ± 0.12 ±0.2 ±0.2
The standard deviation is reported as recommended by Rossini (4); sample weights are corrected to vacuum; and the combustion products in each case are gaseous carbon dioxide, liquid water, and gaseous nitrogen for the reaction at 25°C. The standard deviations given in this paper are about 0.02 per cent of the values reported for the heats of combustion. This compares favorably with the values reported by The National Bureau of Standards, which reports deviations ranging from 0.01 to 0.02 per cent. It is a definite improvement, however, over the 0.1 per cent precision obtained by previous workers in this laboratory (1, 2, 3). In the course of this work a number of additional changes have suggested themselves and will probablj' be adopted as future modifications: (1) The stainlesssteel ignition cup and supports will be replaced by platinum. (2) The energy introduced by stirring should be controlled more closely. A constant-voltage transformer will be tested for this purpose, (o’) The audible interval timer can be made to close the ignition system automatically. This will have two important advantages: first, the precision with which the charge is fired will be improved; and second, the operator will be free to make last-minute temperature readings at the time of ignition. In this work the temperature at the time of ignition was obtained by extrapolation of a smooth curve drawn through previous points. The first author ( . '. S.) wishes to express his appreciation to the Bureau of Aeronautics and the Office of Naval Research for financial assistance. The
500
J. R. PARTINGTON AND
research
tion.
was
A.
L. WHYNES
done under Project SQUID through the Purdue Research Founda-
REFERENCES (1) Grog, R. S., and Hunt, H.: J. Phys. Chem. 46, 1162 (1942). (2) Miles. C. B.. » Hunt, H.: J. Phys. Chem. 45, 1346 (1941). (3) Miller, A. J., » , H.: J. Pliys. Chem. 49, 20 (1945). (4) Rossini, F. D.: J. Wash. Acad. Sci. 29, 416 (1939). (5) W hite, Wt. P.: The Modern Calorimeter. The Chemical Catalog Company, Ine., New York (1928).
THE VAPOR PRESSURE OF NITROSYL CHLORIDE J. R. PARTINGTON
Department of Chemistry, Queen
London, Received
A. L. WHYNES
and
Mary College, University of London,
E.l, England April
20, 1948
The vapor pressure of nitrosyl chloride at low temperatures has been measured by Briner and Pylkoff (1) and Trautz and Genvig (4), but their results differ 15°C. to —70°C., the maximum difference being 140 widely over the range mm. at 45°C. Their results are shown in figure 2, in which logic P is plotted against (1/ T) X 104. In view of the discrepancy the determination has been repeated. —
—
EXPERIMENTAL
To avoid the "tailing” of mercury, Trautz and Genvig placed a thin layer of concentrated sulfuric acid over the mercury in each limb of the U-tube which In the apparatus described below (see figure 1), was used as a null instrument. in contact with a mercury surface, since the not come chloride does nitrosyl is balanced with a pressure glass gauge. Although taps 6 and 7 were exposed to chloride the nitrosyl measurements, it was found that the vacuum grease during used was not attacked for several hours, and it was shown that the pressure was not affected by the grease by sealing off the tubing on the gauge side of taps 6 and 7.
The pumping system consisted of a mercury vapor pump backed by a Cenco Hyvac pump. Attached to the former was a qualitative manometer. A liquidair trap prevented any nitrosyl chloride reaching the pumps. Any substance condensing could be removed by outlet. 14. A large tap (12) connected the pumps to the main vacuum line, tap 11 was used for nitrosyl chloride fractionation in bulb 15, and the three-way tap 5 for the evacuation of the spoon gauge: the pressure in the latter was observed by manometer 2. Pressure in the main line was measured by manometer 1.
