ANALYTICAL EDITION
148
It should be noted that the correction for temperature should always be subtracted while the correction for Pressure should always be added when applied to the factor a t or nearest to the next lower temperature and lower pressure as is recommended for simplicity in the use of the corrections. The general principle of this method of double interpolation may be applied in any caSe of double interpolation from tabulated data.
Vol. 1, No. 3 Acknowledgment
w.
The writers wish to acknowledge their thanks to N. Taylor for suggestions in devising the method used for making the double interpolations, Literature Cited (1) Am. Soc. Testing Materials, Standards, 1927, D271-27, p. 535. Parr, University of Illinois Bulletin, Vol. 1, No. 20 (1924); J . A m . Chem. Soc., 26, 294 (1904). (3) Parr, “Analysis of Fuel, Gas, Water, and Lubricants,” 3rd ed., p. 179. (2)
Specific Heats of Mineral Oils’ Determined by a New Method L. M. Henderson, S. W. Ferris, and J. M. McIlvain THE ATLANTIC REFININQ COMPANY, PHILADELPHIA, PA.
ECENT developments in distillation equipment have increased the need for dependable data on specific heats of mineral oils a t elevated temperatures. It is in this region of elevated temperatures that the present available data disagree. Cragoe has expressed his results by means of the formula A
R
(1)
Presented under the title “Specific Heats 1 Received April 19, 1929. of Mineral Oils” before the Division of Petroleum Chemistry at the 77th Meeting of the American Chemical Society, Columbus, Ohio, April 29 to May 3, 1929. * Italic numbers in parenthesis refer t o literature cited at end of article.
where d = density, t = temperature in O C., and A and B are constants which shows a smaller increase in specific heat with rise in temperature than that allowed by the expression presented by Fortsch and Whitman (2) (t 670)(2.10 - sp. gr.600F.) Specific heat = (2) 2030 where t = temperature in O F. Because of the industrial importance of these equations, the results of an investigation employing an experimental method differing materially from that reported by previous investigators are here presented. The data derived from this work, which was initiated some four years ago, show the same temperature gradient for the specific heat of oils as that given in Equation 2. The actual values of the specific heat vary, however, with the source of the crude oils. This agrees with the findings of Cragoe. For a given temperature and specific gravity, the paraffinic oils show a greater specific heat than the naphthenic oils.
+
Apparatus
A diagram of the calorimeter used in this investigation is shown in Figure 1. It consisted of A , a brass calorimeter
0
4h,
/
2
,NtMfS
BARPEL
Figure 1-Assembly
of Calorimeter
Figure 2-Barrel
a n d Paddle for Calorimeter
3
July 15, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
149
the necessity of ascertaining cooling curves to determine the heat losses. The heat of stirring by either barrel or paddle was found to be very small and the difference was therefore neglected. For the measurements with the paddle we have Qd
+ s ~ =t m $ A T + k A T + L + + +
(3)
For the measurement with the barrel Qzt szt = W Z ~ C A TK A T L (4) By subtracting 4 from 3 and neglecting terms containing s and rearranging, the following equation is obtained where
Q = electrical energy input per second,
in calories in seconds for temperature of oil to rise A T C. calories per second developed by stirring weight of liquid charged, in grams average specific heat of the oil over the range AT apparent average specific heat of the apparatus over the range AT heat lost to environment
t
= time,
s
=
m = c
=
k
=
L =
Keyes and Beattie (4) have suggested the elimination of the heat capacity of the calorimeter bv makina a heatTEMPERATURE ' C Figure 3
proper holding about 580 cc. and surrounded by an air jacket. The heating coil, C, thermometer, D, stirring shaft, E, and the fixed-level draw-off tube, F , were all attached to the calorimeter cover, G, and removable with it. The cover was provided with a brass shield, H I J K . The shaft E was threaded a t the lower end to take either the paddle or the barrel shown in Figure 2. A small hole was bored lengthwise through the shaft to allow for the expansion of the air in the hollow barrel as its temperature was raised. The calorimeter and its accessories were placed in an electrically-heated air bath, which was provided with a multiplicity of fans to insure uniform temperature throughout. A voltmeter and ammeter were used for measuring the energy input, while the electrical energy was supplied by a 36-volt storage battery. The thermometers were of the total immersion type, about 20 em. long, with a range of 70" C., graduated to 0.2" C. and readable to 0.04" C. with the aid of a magnifier. The thermometers were tested one against another with specific reference to thermal lag. Experimental Method
.78-76
-
SPECIFIC HEAT vs TEMPERATURE RELATIONSHIPS
__ I
f
.74 72
.70
.68 .G6
.6+ .62
The method consisted essentially in measuring the electrical energy necessary to raise the temperature of a given weight of oil a definite number of degrees in a definite length of time under carefully controlled conditions. This was repeated after drawing off a large part of the oil and replacing the brass paddle with a barrel of the same material and weight, and therefore of the same heat capacity. The liquid levels were the same in both determinations. This procedure permitted the formulation of the following simultaneous equations, from which the specific heat could readily be calculated inasmuch as the terms involving the heat capacity of the calorimeter and heat loss cancel. This method obviates the use of a liquid of known specific heat for the determination of the calorimeter constant and avoids
.60
.sa .56 I
54
.52
.so .48 .+6
.4 4 .+1 75
1w
12s
is0
175
Figure 4
Zoo
225
250
275
I
150
A N A L Y T I C A L EDITION
----I SOURCE
1 2 3
Pa. distillate Pa. residuum Midcontinent distillate Medicinal white oil Midcontinent residuum Gulf Coast distillate Gulf Coast distillate Gulf Coast distillate Gulf Coast distillate Gulf Coast residuum
? 6 7 8 9 10
16.60
SAYBOLT VISCOSITY
c.
d ~ r . b o c.
0.8750 0.9021 0,8962 0,8546 0.9156 0.9288 0.9450 0,9242 0.8947 0.9465
FLASH
37.78' C. 100' F.
54.4' C. 130' F.
99" C. 210" F.
Sec.
Sac. 101
Sec.
o
297 287
136
i+o ...
304 246 243 51
ii0
219 304 221 199 282 177 171 171
194
... ...
...
... ...
POINT
...
105 110
...
...
Determinations of specific heat were made on ten oils which varied in type from a highly naphthenic Gulf Coast distillate to a paraffinic Pennsylvania residuum. The physical properties of these oils are given in Table I, together with their viscosity-gravity constants ( 3 ) . Oils I, 4, 5, and 9 have been acid-treated and filtered through clay; the others are raw distillates or crude residua. Table I1 presents typical data for one determination, while the experimental values for all the oils are summarized in Table 111. In Figure 4 the specific heats are given for each oil over a temperature range of 25" to 250" C., which necessitated extrapolation of the experimental data for several of the oils. The values calculated by means of Equations 1 and 2 are compared with the experimental data in Figure 3, and it will be observed that in most instances the best line which can be drawn through the points representing the experi-
Initial
5%
of-
or
o
230 238 230 200 284 157 160 149 124 266
252 339 243 227 318 180 181 171 144 274
274
r
230
T a b l e 11-Typical
t ETER
I
CURRENT
E.M.F.
Volts
OC.
Amp.
r
.
0.519 0.814 0.840 0.825 0.834 0.882 0,907 0.880 0.872 0.876
.
253 278 37 1 242 219 241 173 320
D a t a Sheet-Specific Heat R e s i d u u m a t 1 9 7 O C. (Box temperature, 190' C.)
TEMP.
VISCOSITY (37.78' C.) G R A v IT Y CONSTANT
50%
CALORIMNO.
TIME
of P e n n s y l v a n i a
cT$,$Es
"GI,"" Grams
Sec.
Qlt
DETERMINATION OF Q l t WITH PADDLE IN CALORIMETER
I
192 202
26.45 26.45
4.720 4.715
146.6
I1
192 202
26.15 26.15
4.655 4.655
150.0
4363
111
192 202
26.20 26.00
4.655 4.650
160.8
4376
IV
192 202
26.05 25.95
4.645 4.635
153.4
4422
DETERMINATION OF
021 WITH
464.09
4371
Q?t BARREL I N CALORIMETER
I
192 202
21.95 21.95
3.925 3.925
152.0
I1
192 202
22.00 22.00
3.965 3.960
149.0
3104
111
192 202
22.00 22.00
3.955 3.950
151.1
3140
IV
192 202
22.00 22.00
3.940 3.945
149.2
3092
+
Experimental Results
ASSAY DISTILLATION AT 10 MM. PRESSURE
...
...
the barrel and paddle determinations. The heat input necessary to raise the temperature of the oil ATo in an arbitrarily chosen length of time (150 seconds) was determined by making four or five determinations in which the values of t were approximately 150 seconds, and then by plotting the value of Qt against the corresponding heating periods 1 it was possible to ascertain Qt for the definite interval of 150 seconds. Once c had been determined a t several temperatures, the necessity of making both barrel and paddle determinations was eliminated, for the apparatus could then be calibrated according to the equation: Qt - V K A T = k A T + L - st = K In the actual performance of these specific heat measurements, a quantity of oil slightly in excess of that to be used was weighed into the calorimeter and the temperature of both the calorimeter and the air bath was brought to To" C. and held there (+0.2" C.) for 10 minutes. The stirring was then stopped and the excess liquid drawn off into a tared receiver. After this the stirring was again started and the temperature held constant a t TO"C. for a further period of 15 minutes, a t the end of which time the energy input to the calorimeter was increased in such an amount 2") to that the temperature of the oil rose from (To (To 12") in 150 seconds. The temperature of the air bath remained constant a t TooC. during the entire determination. Preliminary measurements of the specific heat of water indicated the method t o be reliable. The average specific heats of water were determined over the .temperature ranges 25" t o 35" C. and 37" to 47" C. and found to be 0.987 and 1.006, which differ, respectively, by 1.07 and 0.8 per cent from the mean values reported in the literature. (The mean values of specific heat of water from data of Rowland, Bartoli and Stracciati, Griffiths, Barnes, Dieterici, and Callendar are 0.99745 a t 30" C. and 0.99773 a t 42" C.)
+
VOl. 1, N o . 3
T a b l e 111-Summary MEAN
T
~ (1)~
c. 37 40 77 80 97 100 127 130 177 180 197 200 227 230 247 250
(2) ~
. . . ... ...
...
0: i 0 3 0.519 0,535 0: i i 9 0 . 5 5 1 0.533 0.574 0.565 0.575 0 . 5 7 0 0.608 0.614 0.622 0.630 0.643 0.636 0.658 0.659 0.653 0.671 0,680 , ,. 0.705
... ... ...
269.19
3129
of Specific H e a t s of Oils Described in T a b l e I
,(3)
(4)
...
0.437 0.450 0.491 0.499 0.524 0.535 0.570 0.567 0,596 0.608
0: 500 0.518 0.519 0.530 0.544 0.544 0.601 0.615 0.620 0.640
(5)
...
(6)
(7)
...
(8)
(9)
0.437 0.448
0 : 4 i 6 0: 460 0:460 0:485 0.483
0.473 0,492 0.498 0.547 0.543 0.556 0.577 0.593 0.614
(10)
... ... I
.
.
0.470 0.467 0 , 4 9 7 0.485 0.490 0.489 0.521 0.512 0 : i o 6 0 , 5 0 0 0 , 5 0 0 0.535 0.525 0.516 0.543 0.532 0.535 0.546 0,537 0.534 0.545 . . . 0 . 5 4 5 0.560 0.573 . . . . . . 0.596 0,570 0.585 . . . . . . 0,605 ... 0.605 0.625 ... ...
...
. I .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o:664 . . . . . . . . . . . . 0:%3 ,,, . . , 0.688 , , , . , , , , , . . , 0 . 7 2 3 ~~
mental values lies parallel to the straight line derived from Equation 2. It coincides with it only in the case of the midcontinent distillate, but this is not unexpected for this equation was derived from measurements made chiefly on inidcontinent oils. It is evident, however, that a correction for the source of the oil is necessary to secure precise results. Specific heats of some paraffinic oils, when calculated with the aid of Fortsch and Whitman's expression, are smaller than the observed values by an amount equal to 0.015 calorie per gram, and for certain naphthenic oils the calculated specific heats are 0.015 calorie per gram greater than those found experimentally. Cragoe has taken this fact into account by assigning to A in Equation 1 the value of 0.425 for paraffin-base oils, 0.415 for mixed-bsse, and 0.405 for naphthenic oils. B is given a constant value of 0.0009.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
July 15, 1929
But despite these corrections for the source of the oils, Equation 1yields low values a t high temperatures. The experimental data obtained in the present investigation indicate that the specific heats of mineral oils a t elevated temperatures can be calculated with the aid of Equation 2 sufficiently accurately to fulfil engineering requirements.
151
Literature Cited (1) Cragoe, International Critical Tables, Vol. 11, 151 (1927). (2) Fortsch and Whitman, IND.END.CHEW,18, 795 (1926); contains a review of earlier work. (3) ill and Coats, Ibid., 20, 641 (1928). (4) Keyes and Beattie, J . Ant. Chem. S O L , 46, 1753 (1924).
The Color of Wheat Flour' Arthur C. Hardy, Prentiss I.Gole, and Charles W. Ricker, Jr. DEPARTMENT OF PHYSICS, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS.
P u r e W h i t e (YI~COJ
Pure W h t e JMqC03
1
6
5
5-
E
G
.r
3
SoSt W \ n t e r W h e a t No. 1 Patent No. 2 S t r a i g h t
No. 3 b a k e v S
e
$ qr
2 0
'
I
l
l
I
;
799
l
8%
were obtained with a sample of hard spring wheat of a patent grade. Curve 1represents the unbleached flour and curve 2 the same flour after bleaching. It will be noticed that the unbleached flour has a lower reflecting power in the blue region of the spectrum, which gives it a yellowish cast. The principal effect of bleaching is to raise the curve in this region of the spectrum, which causes the flour to occupy a slightly higher position
