INDUSTRIAL A N D EXGINEERING CHEMISTRY
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Additional indications of foam quality are given by smallscale field tests, such as the following:
1-A small area of burning gasoline (1x 1.5 meters) may be extinguished with a hose stream and the foam permitted to remain on the surface. After standing over night the foam blanket should not be completely destroyed. 2-Foam projected on a vertical wood surface from a hose stream should cling for several minutes before sliding off, provided the layer is not too thick. 3-1f, after extinguishing a gasoline fire, the foam is carefully pushed back to expose about 400 sq. cm. of the gasoline surface, and the gasoline is reignited, the foam should be sufficiently fluid to flow back and again extinguish the fire.
TESTINQ OF PORTABLE EXTINGUISHERS The tests that have been described are intended to apply to solutions used in fixed systems rather than portable apparatus. I n the case of foam-type hand extinguishers, the only satisfactory test is to discharge the apparatus in the way it is intended to be used, observing the quality and quantity of foam and its effect upon test fires.
IMPORTANCE OF TESTS The principal cause of deterioration of solutions in fixed systems is the loss of carbon dioxide according to the equation: 2NaHCOa = NazCOs 4- COn
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Vol. 16, No. 6
The decomposition is accelerated by high temperatures and exposure of the surface of the basic solution to currents of air. I n portable apparatus the space above the solution surfaces is protected from air currents, and a sufficient concentration of carbon dioxide is maintained practically to establish equilibrium. The loss of gas from fixed systems results in the production of smaller volumes of foam, of less satisfactory quality. It is therefore important to make frequent tests of solutions in fixed systems, determining the volume and quality of the foam and the sodium bicarbonate content of the basic solution. The value of any foam formuIa should be judged by tests of the foam, and also by the ability of the foaming agent to resist decomposition from bacterial action. I n the past too much stress has been placed upon initial expansion, and too little attention given to foam quality and permanence of the solutions. A proper balance of all these factors is necessary to insure satisfactory results from foam fire-protection equipment. ACKNOWLEDGMEKT The writer wishes to acknowledge with thanks the valuable cooperation of Percy A. Houseman in developing the methods herein described, and in the preparation of this article.
Specific Heats of Lubricating Oi Is"' By E. H. Leslie and J. C. Geniesse UNIVERSITY OF MICHIGAN,ANNARBOR,MICH.
HE specific heats of The specific heats were The specific heats of s i x typical lubricating oils have been measured lubricating oils, and determined by measuring over a range of temperatures from 37.78 to 143.33 C. (100 to 290 the rise in temperature reof the heavy fuel oils F.) A n increase of 35 to 40 per cent in specific heats was found. sulting from the passage and residuums, is a subject I t is obvious that a change as large as this must be taken info account of a measured electrical on which the technical literin engineering work. The variation of specific heats with temperacurrent through a resistance ature does not offer an ture is not the same for all oils, and it is suggested that further study coil immersed in the oil in abundance of information. might disclose some connection between the temperature rate of change a calorimeter. I n the design of automotive of specific heats and the properties of an oil as a lubricant. lubricating systems, of apAPPARATUS (FIG.1) paratus in which oil is used The calorimeter consists of a 500-cc. wide-mouth, vacuum as a heating fluid, and of many apparatus such as heat bottle packed in powdered Sil-0-Cel contained in a Parr calorimexchangers used in the oil refinery, knowledge of specific heats eter pail. The heating element is a 61-cm. coil of B. & S. of heavy oils over a range of temperature is necessary. The No. 24 chrome1 wire soldered t o heavy copper leads. The results presented in this paper are not those of an elaborate in- current for heating is drawn from Edison storage cells. The vestigation of the entire subject. Rather, they are of limited stirrer is a small brass propeller run at a constant speed of 1100 p. m. The thermometer is one calibrated by the Bureau of scope and were obtained because of the necessity for their im- r. Standards and graduated to tenths of a Centigrade degree. mediate use in engineering work. The nature and properties The thermometer and leads are supported by a cork that also of the lubricating oils studied are summarized in Table I. The serves to close the vacuum bottle. oils are products made by well-known American manufacturers, PROCEDURE TABLEI-PROPERTIES OF LUBRICATING OILS
T
O
GRAVITY-- --VISCOSITY-TYPEO F PETROLEUM Corrected t o Saybolt Universal F R O M WHICH THE Lu6Oo/6O0 F. 37.78' C. 98.89' C. BRKCATING OILS WERB Oil As Read 15.5"/15.5° C. (100' F.) F.) MANUFACTURED . (210O . A 0.9027 a t Mixture of paraffin235.5 46.3 base and mixed-base 25O C. (77" F.) 0.9077 oetroleums 0.9320 a t 60.2 Mixed-base petroleum 2 2 O C. (71.6'F.) 0.9359 612.5 0,8900 a t 96.5 22' C. (71.6OF.1 0.8939 1190.0 0.9006 a t 199.0 45.3 22O C. (71.6OF.1 0.9045 Mixture of mixed-base 0.9160 a t 688.0 67.0 Oklahoma, Kansas, 123' C. (73.4'F.) 0.9207 a n d Texas petroleum 0.9161 a t 135.0 25O C. (77' F.1 0.9221 2385.0 1 Presented before the Division of Petroleum Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923. 2 Part of the results presented in this paper are published through the courtesy of the Brush Engineering Association of Detroit. --SPECIFIC
11
O
O
In order to determine a specific heat, about 220 grams of oil were placed in the vacuum bottle. A current was then passed through the heating element and the temperature raised somewhat above the lower temperature of the 5' C. interval over which a particular set of observations was to be made. The current was then shut off and the calorimeter system allowed to cool. Readings of time and temperature were taken in order to determine the rate of heat loss. When the temperature had dropped slightly below the lower temperature of the observation interval, the heating current was again passed through the immersed resistance coil. Readings of time, voltage, amperage, and temperature were taken while the temperature rose 5" C., and then the oil was heated to a temperature 1.5"C . or more above the upper temperature
I N D U S T R I A L A N D ENGINEERING CHEiMISTRY
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of the observation interval. The current was then turned off and the calorimeter system again allowed to cool. Readings of time and temperature were also taken during this period. By this means the heat energy supplied to the oil was accurately measured, and the heat loss of the calorimeter system to its environment determined. The specific heat of the oil was then readily calculated. TABLE 11-DATA
O F DETERMINATION 126 Weight of Oil C Used, 224 Grams First Cooling Period Room temperature, 23.3O C. Oil heated to 65.2' C., and allowed to cool to 63.0° C. Time required to cool from 64.0' t o 63.0° C.,376 seconds Heating Period Time Voltage Temperature Seconds Amperage Drop c.
0
0.460 14.85 63.0 0.449 14.82 64.0 0.449 14.80 65.0 0.449 14.80 66.0 0.448 14.78 67.0 577 0.448 14.76 68.0 Average 0.449 14.80 Second Cooling Peviod Room temperature, 23.3O C. Oil heated t o 69.3' C. and allowed to cool to 67O C. Time required t o cool from 68' to 67' C.,313.5 seconds
Table I1 gives the data taken in one determination. The detailed record for d l one hundred and fifty-one determinations is entirely too voluminous for presentation.
CALCULATION Tht: specific heat was calculated as follows: Total energy supplied in small calories = volts X amperes X seconds X factor for converting joules to calories, or 14.80 X 0.449 X 577 X 0.239 = 916.5calories. Energy lost by convection, conduction, and radiation was equivalent to that required to cool the oil. r-n ai t
378 _ _
- 313.5 _
- .1.873'
~
~
C.
2 The heat supplied to the'oil would have raised the temperature of the oil 5.000' 1.673' = 6.673' C. Energy absorbed by calorimeter system is 33.5 X 6.673 = 223.5 calories. Energy absorbed by the oil is 916.5 - 223.5 = 693 calories. Snecific heat of the oil eauals calories absorbed by the oil divided by-iht: product of the temperature rise and the weight of oil, or 693 6.673 X 224 = 0*465
+
DISCUSSION OF RESULTS It will be noted from the foregoing calculation that the rate of heat loss from the calorimeter system to its environment, over the 5" C. observation interval, has been assumed to be the mean of the rates over the upper and lower 1O C. intervals for which time-temperature observations were taken. The procedure based on this assumption proved to be as satisfactory and somewhat quicker than the alternative method of observing the time required to cool over the entire 5" C. observation interval, and more reliable than taking a single set of time-temperature observations over a 1O C. temperature interval from the third to the second degree of the 5" C. observation interval. It should be noted that no correction is necessary for heat added as a result of the conversion of the mechanical energy of stirring into heat, for the effect of this heat i s included in the correction made for heat loss. The stirring must be done at a constant rate, however. TABLE I I I ~ P E C I F I CHEATSO F Oil A
B
C
D E
F
37.78O C.
(looo F.) 0.384 0.385 0.437 0.421 0.411 0.394
65.56' C. (150" F.) 0.449 0.429 0.467 0.451 0.440 0.427
-
LUBRICATING
93.33' C. (200' F.) 0.502 0.485 0.509 0.502 0.498 0.476
- I
._... ... . .
OILS
121.1l0 C. 143.33OC. (250' F.) (290"F.) 0.524 0.555 0.545 0,510 0.558 0.580 0,621 0.546 0.527 0.560 0.535 0.570
--y Of three or four,
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determinations. I n those instances in which there was any doubt as to the value determined, as many as five to seven determinations were made. The results are believed in no case to be more in error than *1.5 per cent and the majority of the values are not more than *1.0 per cent in error. I n general, it is not possible to read the electrical instruments with an accuracy that assures an error less than * 1.0 per cent. In each case the specific heat of the oil increases to the extent of 35 to 40 per cent with rise in temperature over the range from 37.78' to 143.33' C. (100' to 290' F.). Thus the change of specific heat is of such magnitude as to necessitate that it be taken into account in design. The miters are convinced that the irregularities observed are not the result of experimental error. Were the changing rate of increase of specific heat with temperature the 1 I result of vaporization, FIG.1 it would have been most noticeable in the case of the more volatile oils, and would have increased the rate of increase of specific heat with temperature. Both these effects are the opposite of those observed. The changes in the rate of increase of specific heat cannot be attributed to difficulties in the transfer of heat through ineffective stirring, for were this the causative factor the effects would have been exaggerated in the case of the more viscous oils and a t the lowest temperature where all the oils are most viscous. Because of the complexity of the molecules of which these oils are composed and because of the opportunity for molecular association, one would anticipate that their heat capacity would vary markedly with temperature. Unfortunately, the scientific background for the interpretation of phenomena observed in studying the changing thermal capacity of liquids is scanty indeed. No important quantitative generalizations have been developed concerning the heat capacity of mobile liquids. Connected as it probably is with the molecular nature and state, the distinct difference in the temperature rate of change of specific heats of the several oils suggests that a study of the specific heats of lubricating oils might possibly be useful in evaluating oils. At the present time our knowledge of relationships between specific heat, viscosity, adhesiveness, and other physical or chemical properties of lubricating oils is so limited that no conclusions can be drawn. However, since so definite a need exists for methods for ascertaining the value of lubricants, a systematic study of the specific heats of a large number of carefully chosen typical lubricating oils would be justified and might well repay the time and effort required for its completion, The trustees of Columbia University have authorized the exnenditure of $2.375.000 for two new buildinas. one for the Deas soon as funds are available.
