INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1931
was usually about 10 minutes, current and potentia1 to the heater were alternately measured potentiometrically about once each minute. The heat capacities used were the same as those used in the rate-of-cooling method. Discussion The results of the four methods appear in Figure 1. While the individual determinations by any one method are not so concordant as might be desired, no one method is consistently at variance with the others, and all the values are satisfactorily represented by the straight line given in the figure, from which we obtain Specific heat .= 0.388 f 0.00057t where t is the temperatiire in degrees Centigrade.
37
The writers believe that this equation represents the specific heat of diphenyl from its melting point to 300" C . and perhaps higher, to within about 1 per cent. Although higher precision is desirable, the above figures are sufficiently accurate for most purposes, and the absence of any reliable figures in the literature to date justifies the publication of these results. Acknowledgment The authors take pleasure in expressing their indebtedness to the Indian Refining Company for the diphenyl used and for financial aid in the work. Appreciation is also expressed for the helpful suggestions made by F. X. Govers, of the Indian Refining Company.
The Specific Heat of Diphenyl' H. 0.Forrest, E. W. Brugmann, and L. W.T.Cummings RESEARCH LABORATORY OF A P P L I E D
HE increasing use of diphenyl as a heating
T
CHEMISTRY,
DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE OF CAMBRIDGE,
The specific heat of diphenyl has been determined by two independent methods. A batch calorimeter was used in t h e range from 77.6' to 196.5' C., and a flow calorimeter from 147.7' to 347.0" C . The average deviation of t h e experimental points from t h e relation given is less than 2 per cent for both methods.
medium has required an accurate knowledge ofthe heat capacity of this material for the purpose of design of commercial equipment. The variation of the specific heat of the liquid is also necessary for the calculation of tables of thermodynamic properties of this material. Two methods have been used in measuring this property of liquid diphenyl. Experimental Methods BATCH CALORlMETER-The batch calorimeter used is shown in Figure 1. It consisted of a 1-auart (0.95-liter) Dewar flask surroinded by a heatinsulating jacket. The heat was supplied to the liquid by a coil of nichrome resistance wire wound in a Pyrex ring supported on the bottom of the flask. The energy supplied in this way was measured by an ammeter, voltmeter, and stop watch, all of which were calibrated. A motor-driven stirrer was used to mix the liquid thoroughly and maintain a uniform temperature throughout its mass. The temperature was measured a t the midpoint of the liquid with a thermometer graduated in tenths of a Centigrade degree. The flask was filled with a weighed amount of diphenyl such that a vapor space Figure 1 - Batch Calorime- of about 50 cc. was left above the ter liniiid. -~ --1--
The heat capacity of the apparatus was determined using isoamyl alcohol (Merck). The method was checked by determining the heat capacity of water and liquid naphthalene. The temperature of the liquid was measured at 1-minute 1
Received November 12, 1930.
MASS.
TECHNOLOGY,
intervals before, during, and after the h e a t i n g period. The temperature-time relation for a typical run isshown in Figure 2. D u r i n g the heating period the ammeter and voltmeter were read a t
intervals of 30 seconds. FLOW CALORIMETER-The apparatus used in connection with the flow calorimeter method is shown diagrammatically in Figure 3. It consists of a reservoir for liquid diphenyl immersed in a boiling-water bath, from which the diphenyl was displaced with nitrogen pressure greater than the vapor pressure of the diphenyl in any part of the system.
F RATURE-TIME R E L A T W R IFlC HEAT OF LIQUID DlPH
0
I
2
3
4
5
6
7
8
9
10
I1
12
13
14
IS
16
I7
TIME-UINUTES
From the reservoir the liquid flowed through an electrically heated preheater, which brought the liquid to the desired temperature level, and then into the flow calorimeter proper, which is shown in detail in Figure 4. The calorimeter was made of l/rinch (0.13-cm.) extra heavy iron pipe. The mixing chambers were filled with small coils of iron wire and closed on the ends by a metal disk with a '/isinch (1.6-mm.) hole in the center. The heating element was made by winding about 3 feet (0.9 meter) of No. 30 chrome1 wire on a Pyrex-glass worm. The electrical connection to the outside of the apparatus was made through one-piece spark plugs especially selected for
IWDUSTRIAL AND ENGINEERING CHEMISTRY
38
tightness. The space between the porcelain core and jacket of the plug was filled with a water-glass and talc paste as further precaution against leakage. The success of the method depended upon the complete thermal insulation of the calorimeter proper. This was effected by supporting the calorimeter surrounded by 3
N
T'ol. 23, S o . 1
maintained a desired temperature level for a t least 24 hours to bring the calorimeter and lagging uniformly to that temperature. The preheater was also brought to the temperature in question. The flow of liquid was then regulated and the heat to the preheater increased t o heat the diphenyl to the temperature required. Heat was supplied simultaneously in the calorimeter to produce a temperature rise of about 20" C. The rate of flow, rate of heat input to the calorimeter, and the temperature rise were observed a t 15-minute intervals] and calculations were made from the data only after conditions had become steady. In many runs the supply of diphenyl from the storage cylinder was exhausted before this condition was attained with certainty, which accounts for the absence of some runs from the table of data. Method of Calculation and .4ssumptions
A-AMMETER B-DOOW. PLAfFwM MLANCE c-coouffi WIL D- MELTING POT ( S T W Hl*d C-SPAU: FILLED WITH NBWDER PRESSURE h F W W CAWMETER k C M & m OimENYL
L-NEEDLE VALVES N-TO NITROCEN CYUNDER MROUW REWuffi V M P- PREHCATER S- STCAM SUPPLY T- THERMOCOURES V-VOLTMETCR W- BOlllNG WATER WTH - S T W E TANK
Figure 3-Apparatus Diphenyl for theby Determination Flow Calorimeter of the Method Specific Heat of
inches (7.6 cm.) of magnesia lagging in an asbestos board box. This box was in turn surrounded by a constant-temperature gas bath. The liquid diphenyl from the calorimeter was cooled as it passed through the coil in the water bath. The rate of flow was regulated with a needle valve, and the rate measured by noting with a calibrated stop watch, the time required for 100 grams of liquid to flow out into the receiving bottle on the balance. The temperatures in the calorimeter were measured with chromel-cope1 thermocouples calibrated before and after the experiments. The cold-junction box was a 1-quart (0.95 liter) Dewar flask filled with cracked ice. A Leeds and Northrup type K potentiometer and a galvanometer sensitive to 0.001 millivolt were used to measure the potentials generated. The energy supplied to the heating coil of the calorimeter was measured with a calibrated voltmeter and ammeter. The system was operated as follows: The gas bath was
It has been assumed that over the temperature interval-about 11" C. in the batch and 21' C. in the flow calorimeter experiments-t he average specific heat was equal to the specific heat a t the average temperature. Liquid I n the batch calorimeter experiments the timetemperature data were plotted as shon-n in Figure 2 and joined &th straight lines. The extrapolation of-the two cooling curves and the heating curve gives two intersections which when subtracted give the apparent rise in temperature. The true temperature rise is obtained by adding to the apparent temperature rise the average of the temperature drops due to loss of heat during the heating period as determined from the cooling curves. The heat capacity of the batch calorimeter n a s assumed to be constant over the temperature range investigated. It was assumed that the heat loss from the flow calorimeter was negligible. The factor used to convert 11-att-seconds to gram-cdories was the reciprocal of 4.18. Results
The data and calculated results are given in Tablei I and 11. The values of the specific heat of diphenyl obtained for both experiments are plotted in Figure 5. It is t o be
Table I-Batch Calorimeter Data and Results Heat capacity of apparatus, 47 calories per degree Centigrade, based on specific heat formula for isoamyl alcohol from I. C. T . : Cp = 2.101 0.01021 t 4- 0.0000171 where C p = joules per gram and t = degrees Centigrade
+
TEMP. CORRECTIOX FOR
WT. OF HEAT R U N DIPHENYLLoss 11 18 16 19 20 21 22 23 24 25 26 27 23 29 30 31 32 33 34 35 36 37 a
Grams 535 525 525 532 506 506 506 504 504 504 568 568 568 568 575 576 575 578 575 575 575 575 Corrected.
C. 1.04 0.96 1.05 1.11 1.05 1.09 1.19 0.34 0.51 0.68 1.29 1.39 1.46 1.62 1.39 1.46 1.76 1.73 1.85 1.56 1.65 1.91
TEMP. RANGE^
c. 131.55-141.93 121.60-132.56 130.67-142.14 120.88-131.11 121.89-131.53 129.35-138.72 137.10-140.47 71.79- 8 3 . 4 4 82.58- 94.22 90.46-102.87 144.80-155.68 153.04-164.29 158.46-170.98 167.86-180.50 151.00-162.89 159.97-171.06 170.18-181.32 178.18-189.62 189.63-200.78 171.34-183.56 178.11-189.85 190.02-202.94
TEMP. RISE& E. M.
*
c.
10.38 10.96 11.47 10.23 9.64 9.37 12.37 11.65 11.64 12.41 11.38 11.25 11.52 12.64 11.89 11.09 11.14 11.44 11.15 12.22 11.74 12,92
Volts 17.2 20.3
18.6
17.6 16.1 16.0 18.7 17.1 16.9 17.0 21.1 21.1 22.7 22.8 22 0 22.0 21.4 22.3 22.3 22.8 22.8 24.0
HEAT HEAT INPUT TO ABSORBED H E A T CALOBY ABSORBEDSPECIFIC TIMEOF RIMEAPPARA- BY HEATOF CURRENTa HEATING@ TER TU8 DIPHENYLDIPHENYL Gram-cal./ Sec. Gram-cal. Gram-cal. Gram-cal. cram/' C. Amp. 311417 487 _... 2.553 0,460 2.46 300 240 2535 0.440 2.62 3050 ii5 2724 0.453 2.44 300 3260 536 2480 0.455 2.34 300 2960 480 2166 0.445 2.27 300 2620 454 2600 440 2160 0.455 2.26 300 2930 0,468 2.61 300 3510 580 2400 0.408 2.40 300 2950 550 2460 0.418 3010 550 2.36 315 2566 0.410 2.42 320 3150 584 3025 0.468 2.35 300 3560 535 3030 0.475 2.35 300 3560 530 3550 0.499 4140 590 2.54 300 3575 0.497 2.55 4170 595 300 3290 0.482 3850 560 2.44 300 3270 0.513 3790 520 2.40 300 3135 0.489 3660 525 2.38 300 3422 0.520 3960 538 300 2.47 3435 0.536 3960 525 2.47 300 3555 0.505 4130 575 2.52 300 3578 0.530 300 4130 552 2.52 3972 0.534 4580 608 300 2.66 I
,
DEVI4TIOV
Av.
TEMP.
c. 136,i 127.1 136 4 126.0 126.7 134,O 143.3 77.6 88.4 96.7 150.0 158.7 164.7 174.2 156.9 165.5 175.8 183.9 195.2 177.5 184.0 196.5
FROM
CURVE
70
t o . 87
-1.35 -0 66 +2.24 0.00 +0.23 +0.86 +0.49 +1.45 -1.91 -0.85 -1.65 +1.63 - 1.78 +0.21 +4.48 -3.74 0.00 -0.37 -0.98 f1.73 -1.29 Av. 1.64
INDUSTRIAL A N D EiVGI NEERING CHEMISTRY
January, 1931
observed that in the range from 147.7' to 196.6" C. there are twelve experimental points from the batch calorimeter and 4 from the flow calorimeter experiments. The average deriation of the experimental values from the curve drawn is less than 2 per cent. The maximum deviation is 4.5 per cent. Table I11 gives the values of the specific heat of water and naphthalene determined in the batch calorimeter compared with the best values of the specific heat of these substances. Table 11-Flow
Calorimeter Data and Results HEAT Av. RECIP-
TO TEMP. C U R R U K RISE REST
a
16A 16B 17 18 1SB 20 27 28
E. M. F.
DrPHENYL
2.39 2.39 2.20 2.29 2.30 :.45 -.45 2.40
36.8 36.8 33.7 35.0 35.2 37.8 38.0 37.0
21.0 21.0 17.7 19.2 19.4 22.2 22.2 21.2
Table 111-Specific
C. 191.5 192.5 185.0 147.7 248.8 307.0 346.0 347.0
C. 185 185 197 145 230 2 86 336 335
65.4 66.0 59.8 56.1 59.0 60.1 69.4 69.2
CIFIC
DEVIATION FROM
Gramtal./
C. 0.534 0.534 0.512 0.470 0.618 0.645 0.665 0.672 Av.
The assumption that the flow calorimeter lost no appreciable amount of heat during a run is justified by the fact that in some runs the inlet temperature would vary a few degrees while the difference between the inlet and outlet temperatures would remain constant. The fact that the heater coil was in the center of the calorimeter, and the flow was viscous, resulting in the insulation of the heated diphenyl by the cooler film a t the container walls, justifies this assumption further. As discussed above, the assumptions made are justifiable within an accuracy of 2 per cent. The batch calorimeter not only gave consistent results on the specific heat of diphenyl, but also gave values for the specific heat of water and naphthalene which check the best reported values with the desired precision.
% $0.38 0.00 -1.91 0.00 S0.65 -1.07 -0.48 4-0.60 0.63
Heat of Water and Naphthalene WATER 1 3 42 30
Run Temperature, C. Specific heat: Determined Bureau of Standards0 Deviation, per cent
SPR-
RATE TEMP.TEMP. HEAT CURVX
Gram- S a . / 100 cal./ sec. grams
C. .-Imp. Volh
25.7 26.2 20.; 22.9 18.5 20.4 23.1 21 5
DIBATH PHENYL
ROCAL
39
4 40
o
46
6 46
1.01 1.00 0.98 0.99 1.00 0.997 0.997 0.997 0.997 0.997 $1.00 $ 0 . 3 0 - 1 . 7 0 -0.70 $0.30 NAPHTHALENE 12 17 18 128.0 129.5 127.0
Rim Temperature. ' C . Specific heat: Determined I. C. T. Deviation. per cent J f e r h E n g . , 51, 126 (1929).
0.432 0.422 $2.37
0.434 0.424 4-2.36
0.431 0,422 $2.13 eo
Discussion of Results
The specific heat of diphenyl over a small temperature interval, 10" to 20" C., is practically linear, and therefore the assumption that the average value of the specific heat over the interval is equal to the specific heat a t the average temperature does not introduce an appreciable error.
a6
ua
20
40
eo no
200 K) 40 eo TEMPERATURE, .C.
no 300 20
40
eo no
Specific heats of diphenyl determined by the flow method are consistent within themselves, as shown in Figure 5. The fact that the values determined by this independent method agree with those determined by the batch calorimeter method over the range of 147.7" to 196.5' C. confirms the accuracy of the flow-method data. It is unfortunate that it was not possible to determine data a t higher temperatures to indicate the point a t which the specific heat again resumes its upward trend. Conclusion
As a result of this investigation a curve has been obtained which gives the specific heat of diphenyl within 2 per cent a t temperatures from 77.6' to 347.0" C. H
5'
C-COUAIL55ON C C M S S-SWRK PLUG
Acknowledgment
W-UEATTINC COIL
Figure 4-Detail
of Flow Calorimeter
In-tlie batch calorimeter calculations the assumption used that the heat capacity of the apparatus did not vary is justified by the fact that in this temperature range the specific heat of g l a ~ sdoes not change rapidly. This is particularly true since a change of 10 per cent would be necessary to alter the specific heat of the diphenyl by 2 per cent. The correction for heat loss in the batch calorimeter experiments n-as less than 20 per cent, and has been accurately accounted for, The batch calorimeter has produced data on the specific heat of water and naphthalene which compare favorably with data of other investigators within the limit of experimental error ( 2 per cent).
Acknowledgment is made to the Swann Chemical Company, Federal Phosphorus Division, rrhich gaye financial support to this investigation. Thanks are also due 11. A. T'olante and F. W. Stones rrho carried out the experimental m-ork. New Method of Road Leveling--% new process for raising sunken parts of concrete highways has been invented and patented by John Poulter, a mechanic of the Iowa Highway Commission. By this process a mixture of mud and cement, pumped beneath the concrete through holes drilled in its surface, spreads out between the concrete and the ground, forcing the concrete up. Later it hardens in place. The chief advantage of this method is that it is cheap and it cures the settlement a t the source of trouble by filling the voids underneath the pavement.
