I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
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Summary
Clays, kaolin, and pulverized talc have been found inefficient in absorbing iron from aqueous solutions of sulfates. Various forms of charcoal show wide variations in effectiveness as adsorbers of iron from sulfate solutions. Animal charcoals are much more effective than vegetable chars. With alum solutions, alumina is also adsorbed in amounts sufficient to prove impracticable the using of chars. A permutite of the glauconite type is reasonably effective in removing iron from sulfate solutions. From the nature of the reactions involved, the removal is never complete. Working with diluted solutions, the remaining concentration of iron may be brought to a very low figure. Too low concentrations, however, may effect removal of iron from the per-
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mutite with consequent contamination of the solution by iron. Literature Cited (1) Fodor and Rosenberg, Kolloid-Z., 46, 91 (1928). (2) German Patent 232,563 (1908), Chem. Fabr.-Griesheim-Elektron, Frankfurt; C. A . . 5, 2709 (1911). (3) Griffin, "Technical Methods of Analysis," McGraw-Hill, 1927. (4) Hultman and Linblad, Swedish Patent 53,134 (1922); C. A . , 17, 3407 (1923). (5) Kolb, Chem.-Zfg., 35, 1393 (1911). (6) Magistad, Arizona .4gr. Expt. Sta., Tech. Bull. 18, 445 (1928); C. A . , 22, 3595 (1928). (7) Norske Aktieselskab for Electrokemisk Ind. Norsk Industri-Hypotekbank. British Patent 123,720 (1918); C. A . 13, 1624 (1919). (8) Vittorf, Trans. Inst. Econ. Mineral. Pelrog. (Moscow), 1934, No. 8, 1-16; C. A , , 20, 1497 (1926). (9) Zabicki, Prsernysl Chem., 12, 77 (1928); C. A , , 22, 2641 (1928).
Thermodynamic Properties of Dichlorodifluoromethane, a New Refrigerant' IV-Specific Heat of Liquid and Vapor and Latent Heat of Vaporization Ralph M. Buffington and Joseph Fleischer FRIGIDAIRE CORPORATION, DAYTON,OHIO
T
HIS paper covers the
experimental determination of some thermal properties of dichlorodifluoromethane and completes the report of the experimental data necessary for the construction of tables of thermodynamic properties of this substance. Specific Heat of Vapor
The specific heat of dichlorodifluoromethane vapor at atmospheric pressure was measured in a flow calorimeter at 0', 25.S0, and 49.9"C., the experimental data fitting the equation, C, (molal) = 17.0 0.0279t (tOC.) The heat capacity of the liquid was measured as 30.3 calories per mole per C. at 17" C., using the method of mixtures, and as 25.4 at -43' C., using an electrical heating method. The latent heat of vaporization was determined by an electrical heating method as 4880 calories per mole at the boiling point, -29.8' C.; 4100 at 23" C.; and 3960 at 28" C. The ratio C,/C, for the vapor at 25' C. and atmospheric pressure was determined by the Kundt method as 1.139.
+
O
The specific heat of the vapor a t atmospheric pressure was measured a t three temDeratures in a flow calorimeier. The apparatus, which is illustrated in Figure 1, consisted of a 500-cc. Dewar flask fitted with a tight rubber stopper carrying a vapor inlet and a vapor outlet tube. The outlet tube was thermally insulated from the remainder of the apparatus by means of a silvered vacuum jacket. A 115-ohm nichrome heating coil was inserted in the lower end of the outlet tube; directly above it were placed several disks of copper gauze for the purpose of insuring temperature equilibrium in the vapor. As a further precaution against heat loss, the lower end of the outlet tube was inserted in a glass cup, which caused the cold gas to flow around the outside of the heater tube. Copper-constantan thermocouple junctions were placed in the inlet and outlet tubes, each junction being soldered to a disk of copper gauze. Both junctions and also the heating coil were enclosed in radiation shields of aluminum foil. The calorimeter was totally immersed in a thermostat, the temperature of which was controlled to *0.05" C. by a thermoregulator at the two higher temperatures; closer temperature control was obtained a t 0" C. by thorough stirring of an ice-and-water mixture. The vapor was passed through 12 meters of flattened copper coils immersed in the thermostat 1
Received July 13, 1931.
before entering the calorimeter. A steady flow of vapor was maintained by boiling liquid contained in a 1-liter Dewar flask with a constant heating current; different rates of vapor flow were obtained by varying the current. Measurements of the rate were obtained by noting the weight of the container at measured time intervals. A capillary flowmeter, attached to the outlet tube of the calorimeter, served to give a visual indication of the constancy of flow. The calorimeter heating current was obtained from lead storage cells; various heating rates were obtained by varying the number of cells used. The input of electrical energy was determined by measuring the voltage across the heater with a voltmeter and the current through the heater by the potential drop, measured with a potentiometer, across a standard 1ohm resistance in series with the heater. The temperature rise produced in the vapor was measured by means of the differential couple, the e. m. f. developed being measured with a Leeds and Northrup type K potentiometer. The thermocouple wire had been carefully calibrated, so that the temperature coefficient of its e. m. f. was known over a wide temperature range. The thermocouple junction in the inlet tube also served as the hot junction of a second couple, the other junction of which was kept a t 0" C., which was used to measure the temperature of the inlet vapor. The experimental data given in Table I were obtained by averaging the measurements taken over periods of at least l/2 hour, after conditions had become steady. It was found that, a t rates of vapor flow below 400 grams per hour, the measured specific heat became larger the slower the rate of flow, while
November, 1931
INDUSTRIAL AND ENGINEERTNG CHEMISTRY
above this minimum rate, the measured specific heat was independent of the rate of flow. No correction was applied for heat leak, since the results show that it was within experimental error for the temperature rises measured. The experimental results are satisfied by the following empirical equation for the molal h e a t c a p a c i t y , which is believed t o be accurate to within 1 per cent over the temperature range covered by the experiments, 0" C. to 50" C.:
Cp = 17.0 f
0.02791 ( t o C.)
Specific Heat of Liquid
The specific heat of liquid dichlorodifluoromethane at r o o m t e m p e r a t u r e was measured by the method of mixtures. The liquid was sealed into a brass cylinder of a b o u t 50 cc. capacity; only a v e r y s m a l l v a p o r space was present, so that vaporization and condensation corrections were negligible. A 500-cc. D e w a r flask Figure 1-Flow Calorimeter c o n t a i n i n g 150 grams of water served as the calorimeter. Its water-equivalent, including the Beckmann thermometer and stirrer, was measured as 379 grams by an electrical heating method. The water equivalent of the brass container was calculated as 6.207 grams from its weight and the specific heat of brass; that of the 67.0 grams of liquid was determined experimentally as 16.8 grams. Data and Results for DichlorodifluoroTable I-Flow-Calorimeter m e t h a n e Vapor a t Atmospheric Pressure HEATINPUT VAPORFLOW TEMP. RISE CP Cal./hour Grams/hour c. Ca2./mol./o C. 00 c. 1 513.8 701.3 5.22 16.97 17.00 2 802.0 871.0 6.55 17.03 3 808.7 1007.0 5.70 828.0 4.44 17.04 4 518.2 17.06 5 808.7 828.0 6.92 Av. 17.02 25.8' C. 1 447.2 802.2 3.80 17.74 17.89 2 516.6 554.0 6.30 3 516.5 642.8 5.47 17.76 4 805.6 1074.6 5.16 17.57 5 803.7 837.0 6.63 17.51 6 515.6 670.0 5.22 17.82 7 515.6 845.0 4.21 17.62 Av. 17.69 49.90 c. 1 515.0 837.0 4.01 18.55 2 804.6 1002.8 5.27 18.41 3 515.4 649.8 5.18 18.51 4 291.9 650.0 2.96 18.34 5 513.4 840.0 4.01 18.43 6 803.2 834.8 6.35 18.32 Av. 18.42
The experimental procedure consisted in measuring the calorimeter temperature every minute until it was changing regularly; then the container, which had been brought to a definite temperature in a thermostat, was quickly dropped in and temperatures again read every minute for 15 or 20 minutes. Extrapolation to the time of adding the container gave the temperature rise of the calorimeter. The data obtained are given in Table 11. The specific heat at the average mean temperature, 17" C., is 0.251 calorie per gram per " C.,
or 30.3 calories per mole per about 4 per cent.
1291 O
C., with a probable accuracy of
Table 11-Calorimetric Data a n d Results (Method of Mixtures) for Liquid Dichlorodifluoromethane TEMPERATURE CHANGES Calorimeter Sample MEANTEMP. SP.HEAT * c. a c. O c. Cal./sram 1.43 0.251 23.42 17.4 24.77 17.0 1.55 0.261 1.49 24.50 16.0 0.251 24.90 17.0 1.53 0.255 0.246 23.45 18.0 1.405 22.70 18.0 1.38 0.251 0.246 18.36 14.8 1.10 14.2 0.249 17.20 1.04 0.248 27.50 18.0 1.66
The specific heat of the liquid at -40" C. was measured by an electrical heating method. A 250-cc. Dewar flask, provided with a heating coil and stirrer and immersed in a cooling bath of solid carbon dioxide and acetone, served as the calorimeter. Temperatures were measured by means of a copper-constantan thermocouple, used in conjunction with a Leeds and Northrup type K potentiometer. The rate of temperature rise of the liquid with a known input of electrical energy was determined by measuring the temperature of the liquid every 2 minutes during a 20-minute heating period, as well as before and after this period. The water equivalent of the calorimeter was determined by experiments with methanol. The average of several determinations made with samples of about 300 grams of liquid dichlorodifluoromethane gave a specific heat of 0.21 calorie per gram per " C., or 25.4 calories per mole per " C. a t -43" C. with a probable accuracy of 4 per cent. Latent Heat of Vaporization
The latent heat of vaporization a t the boiling point was determined by an electrical heating method. The liquid w a s c o n t a i n e d in a 1-liter Dewar flask provided with a h e a t i n g coil and baffles to prevent loss of l i q u i d as spray. T h e experimental procedure consisted in measuring the loss in weight for a definite input of electrical energy. The rate of vaporization a n d t h e weight of liquid evaporated were v a r i e d in the i n d i v i d u a l runs. The following are the e x p e r i m e n t a1 values o b t a i n e d , each value being corrected for the v a p o r i z a t i o n of the weight of vapor replacing the volume of liquid evaporated: 40.0, 40.3, Figure 2-Latent-Heat Calorimeter 41.1, 40.3, a n d 40.2 calories per gram. The average of these values for the latent heat a t -29.8" C., 40.4 calories per gram or 4880 calories per mole, is judged to be accurate to within 2 per cent. Two determinations of the latent heat were made a t room temperature in the isothermal calorimeter illustrated in Figure 2. This consisted of a welded steel container provided with a needle valve and a nichrome heating coil, the whole being inserted in a block cork jacket. With a constant input of electrical energy, the rate of evolution of vapor was con-
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trolled by means of the needle valve so as to maintain a zero temperature difference between the container and the jacket as indicated by a difference thermocouple. The values determined are 33.9 calories per gram (4100 calories per mole) at 23" C., and 32.8 calories per gram (3960 calories per mole) at 28" C., with an estimated accuracy of 2 or 3 per cent. Ratio of Specific Heats of the Vapor
The specific-heat ratio C,/C. = y, of dichlorodifluoromethane vapor was measured a t 25" C., and atmospheric pressure by the Kundt method. The velocity of sound in the vapor relative to that in air was measured in a Pyrex tube, 4.3 cm. in diameter and 135 cm. long, a t a frequency of approximately 2700 cycles per second. The sound waves were produced by stroking a clamped brass rod with a cloth moistened with methanol and were transmitted t o the air or vapor by means of a thin brass disk mounted on the end of the rod, just inside the end of the tube. Resonance was obtained by moving a similar disk in the other end of the tube; the positions of the nodes were indicated by cork dust. Displacement of the heavy vapor by air was prevented by tying thin sheet rubber over the ends of the horizontal tube and by maintaining a slow stream of vapor through the tube with upward exit. The measured velocity ratio relative to air was 1:2.298. Several other measurements of somewhat less accuracy gave values for the ratio within less than 0.5 per cent of this figure.
I n particular, reduction of the tube diameter from 4.3 to 2.0 cm. did not affect the result within the limit of error of individual determinations; therefore no tube correction was applied. The velocity of sound in air a t 25" C. was calculated from the equation in the International Critical Tables ( 3 ) , with a slight correction for 3 mm. partial pressure of water vapor as 34,640 cm. per second. The velocity in the dichlorodifluoromethane was therefore 15,073 cm. per second. The value of y was then determined as 1.139 * 0.005 by substituting the proper values in the following form of the Laplace equation (2):
W M V ($)T
= velocity of sound = 15,073 cm. per sec. = molecular weight = 120.9 = volume per mole = 25,000 cc. =
-38.42 dynes per sq. cm. per cc. per mole
The values for V and
(g)T
a t 25' C. and 0.96 atm. were
obtained from the equation of state ( 1 ) .
Literature Cited (1) Buffington and Gilkey, IND. ENG. CHEM.,23, 254 (1931). (2) Cornish and Eastman, J . Am. Chem. SOC.,50, 639 (1928). (3) International Critical Tables, VI, 462 (1926).
Thermodynamic Properties of Dichlorodifluoromethane, a New Refrigerant V-Correlation, Checks, and Derived Quantities' Ralph M. Buffington and W. K. Gilkey FRICIDAIRE CORPORATION, DAYTON,OHIO
This is the concluding member of a series of papers contains, i m p l i c i t l y or exHIS p a p e r completes which provide the basis for engineering tables of the plicitly, consistent values of the report of a program 0f resear ch thermodynamic properties of dichlorodifl,uoromethane. a l l t h e t berm 0 d y n a m i c Application of thermodynamics to an equation of state quantities which are of inwhich was undertaken for the for the vapor, to a vapor pressure equation, to a graph terest. The network is then purpose of providing the basis of the density of the liquid, and to an equation for the checked a t various points by for thermodynamic t a b l e s specific heat of the vapor at 1 atmosphere, results in a means of additional secondneeded in t h e d e s i g n and operation of dichlorodifluoronetwork, which contains consistent values of all the ary data, and perhaps by required properties, for the region between the isomeans of empirical rules, thus methane refrigerating equipmerit. The e x p e r i m e n t a l metrics which correspond t o saturation at -40' and m a i n t a i n i n g a continuous 50" C. The network is checked by means of secondary check on its accuracy. data, and e q u a t i o n s a n d data. Derived results are given, in the form of equagraphs r e p r e s e n t i n g them, Thermodynamic Network tions or graphs, for the following: the latent heat of have been given in e a r l i e r vaporization L; C, and C, of the vapor; C, of the The network has been built papers of the series, and the liquid; and the entropy s and heat content H of the up from the following: an tables have been published elsewhere (4). It remains liquid, saturated vapor, and superheated vapor. equation of state for the superheated vapor ( 3 ) , a vaporfor this paper to present the correlation of the data, the thermodynamic checks, and the pressure equation (5),a graph of the density of the liquid ( I ) , and an equation for the specific heat of the vapor at atmoscalculation of derived quantities. Because of the thermodynamic relations existing between pheric pressure ( 2 ) . The notation used is as follows: the various properties, there is room for only a few independent equations expressing experimental results. The procedure adopted has therefore been to determine experiC, = specific heat a t constant pressure in cal. per gram mole c. m e n t a b a few fundamental quantities Over a range of presheat at constant volume in tal. per gram mole c, = sure and temperature and express the results empirically, c. V = volume of vapor in liters per gram mole and then to combine them with exact thermodynamic formulas, thus constructing a thermodynamic network which P = pressure in atmospheres
T
T = absolute Centigrade temperature ( " C.
1 Received
August 13, 1931.
v
+ 273.1)
= volume of liquid in liters per gram mole
