1-VDUSTRIAL AND ENGINEERING CHEMISTRY
366
where p is the vapor pressure in absolute atmospheres; T is the temperature in degrees Kelvin (" C. 273.1).
+
Vol. 23, No. 4
and the equation of state (1) is 20.0. The Hildebrand constant is 27.1.
Discussion
Acknowledgment
Figure 1 shows the deviations of the observed data from the equation. The data of each observer are well represented by the equation. These deviations are random with respect to observer, sample, and order of observations on each sample. The dotted lines A A show the deviations from the equation assuming a 1 per cent error in pressure measurement. Lines BB show those due to an error in 0.1' C. in temDerature. The boiling point as calculated from the equation is f29.8" C. The 'Onstant as from the Of log p ,/ d a t the boiling point, the density of the liquid,
(+)
The writers gratefully acknowledge the assistance and suggestions of R. under whose direction this work was done, and of F. Bichowsky. They also wish to thank F. B. D o w i n g and A. F, Benning, of the Laboratory of E. 1,du pant de Nemours and Company, for criticisms offered during the course of this investigation. Literature Cited (1) Buffington and Gilkey, IND.ENO. CHEM.,23, 254 (1931) (2) Hildebrand, J . Am. Chem. Sot., 37, 970 (1915). (3) hlidgley and Henne, IND.END. CHEM.,22, 542 (19501
I I I-Cri tical Constants and Orthobaric Densities' F. R. Bichowsky and W. K. Gilkey FRIGIDAIRE CORPORATIOX,DAYTON, OHIU
I
N ORDER to calculate the heats of v a p o r i z a tion and other thermodynamic properties of dichlorodifluoromethane from the vapor p r e s s u r e s , the o r t h o b a r i c d e n s i t i e s are needed. Density of Saturated Vapor
The orthobaric densities of dichlorodifluoromethane have been measured up to the critical temperature, and the critical constants determined. The saturated vapor densities below 50" C. were calculated from the vapor-pressure equation and the equation of state. Above 50" C. they were obtained by determination of dew points. Liquid densities from -40' to 50' C. were determined by a dilatometric method, and above 50" C. by Faraday's method, using glass floats. The critical temperature, pressure, and density are, respectively, 111.5' C., 39.56 atmospheres, 0.555 gram per cubic centimeter.
The density of the saturated vapor may be calculated from the equation of state ( I ) ,
p where A = 23.7 (1
=
RT
(V+ B)
A - v*
-
Preliminary determination of the density of the liquid
Table 11-Densities
p
= pressure in atmospheres V = volume in liters per gram mol T = absolute Centigrade temperature
by introducing the corresponding pressures and temperatures from the vapor-pressure equation (2): 1816.5
-T - 10.859 loglo T + 0.007175 T
and solving for the volume. The computed values are given in Table I. Table I-Volume and Density of Saturated Vapor, as Calculated from Equation of State and Vapor-Pressure Equation TEMP. DENSITY VOLUME TEMP. DENSITY VOLUME Cc./gram Cc./gram C. Grams/cc. Grams/cc. C. 10 0.02379 42.04 244.1 0.004097 -40 20 0,03149 31.75 161.3 0,006199 -30 30 0.04111 24.33 110.7 0.009037 -20 40 0.05313 18 82 78.13 0.01280 -10 0 0.01765 56.67 50 0.06856 14 59
These values have a probable error of k l . 0 per cent. At temperatures above 50' C. this equation of state fails and we depend on two determinations of the dew point. The values are d = 0.202 a t 94.4" C. and 0.168 a t 86.7" C. These dew-point determinations were made in small glass tubes and are probably accurate to * l per cent. Direct observations of the critical point showed that the IReceived
Density of Liquid
gave the density a t 0" C. as 1.40 and the coefficient of expansion, 0.00233. These values have been superseded by very careful determinations, by a dilatometric method, of the density by F. B. Downing and A. F. Benning, of the Jackson Laboratory of the E. I. Du Pont de Nemours and Company. Their values are given in Table 11. TEMP. O c .
loglo p = 31.6315
critical phenomena were unusually sharp and that the critical t e m p e r a t u r e mas 111.5 * 0.5' C.
January 31, 1931.
-37.8 -28.4 -23.9 -17.8 - 9.60
of Liquid
DENSITY Grams/cc.
TEMP. c.
1.5095 1.4822 1.4689 1.4511 1.4254 1.3946
13.8 25.6 35.1 35.2 46.9 56.5
DENSITY Grams/cc.
1.3521 1,3081 1.2725 1.2722 1.2260 1.1834
The densities a t higher temperatures were determined by Faraday's method-that is, by the use of small floats in a sealed tube. The values obtained were 0.9785 at 91.1" C., 0.910 a t 98.9" C., 0.814 at 106.7" C. The estimated error was +0.5 per cent. Computed Densities-Rectilinear Constants
Diameter-Critical
These various determinations, together with the points determining the rectilinear diameter, are shown graphically in Figure 1. Table I11 gives interpolated densities at even temperature intervals. Table 111-Density of Liquid DENSITY Liquid Vapor Gram/cc. Grams/cr. 0.004097 1.517 0.006199 1.486 0.009037 1.456 0.01280 1.425 0.01765 1.393 0.02379 1.362 0.03149 1.329 0.04111 1.293 0.05313 1.155
and Saturated Vapor
TEMP.
TEMP.
* c.
* c.
- 40 - 30 -20 - 10
0 10 20 30 40
50 60 70 80 90 100 110 111.5
DENSITY Liquid Vapor Grams/cc. Gram/cc.
1.213 1.165 1.115 1.056 0.988 0.898 0.725 0.555
0.06856 0.0875 0.111 0.142 0.182 0.242 0.380 0.555
April, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY (di
367
+ d v ) / 2 d c = 1 + 0.963 (1 - T / T J
The coefficient 0.963 is that of a normal liquid (3). The critical volume is 1.80 cc. per gram. The critical density, d,., is 0.555 gram per cc. A short extrapolation of the vapor-pressure curve gives for the critical pressure, p,, 39.56 atmospheres. The critical temperature is 111.5" C. The ratio of the absolute boiling point to the critical temperature is 0.632. The conventional constants a and b of the van der Waals equation are:
m
l J = -
8 X 273.1
- 0.00445 -
Acknowledgment
DENSITY-GRAMS PER c c F i g u r e 1-Orthobarlc Volumes and R e c t i l i n e a r Diameter
+
The rectilinear diameter-namely, (di d0)/8-is almost exactly a straight line given by the equation (di f &)/2
=
0.555
+ 0.00139 (Le - t)
or in terms of reduced densities and temperatures,
The authors wish to thank F. B. Downing and A. F. Benning, of the Jackson Laboratory of E. I. Du Pont de Nemours and Company, for permission to publish the accurate series of liquid density determinations given in this paper. Literature Cited (1) Buffington and Gqlkey, IND. ENG. CHEM.,23, 254 (1931). (2) Gilkey, Gerard, and Bixler. I b i d . , 23, 364 (1931). (3) Laar, van, "Zustandsgleichung von Gasen und Flussigkeiten," p . ,341, Leipzig, 1924.
Hydration of Animal Skin by Volume-Change Method IV-Effect of Various Factors upon the Hydration of Calfskin' Edwiri R. Theis and F. T. Benton* DEPARTMENT OF CHEMICAL EXGINBERING, LEHIGHUNIVERSITY, BETHLEHEM, Pa.
The hydration of calfskin has been measured w a n metric method was a compresREVIOUS papers (3, 4, 5 ) have described the titatively. The effects of post-mortem action, upon sion of the water within the hydration changes that the potential hydration capacity of calfskin, have skin and that this compression been shown. It is pointed out that if the hydration was of the order of 1000 attake place during the soaking and liming of heavy hides. capacity of hides and skins is to be conserved, the skins mospheres per gram of gelatin A method of measuring hyshould be cured as soon as possible after death. in 150 ml. of water at 0" C. dration by the volume change The effects of salt solutions of various concentrations I n the previous work, the method was described. This upon the hydration of fresh calfskin are shown and hydration as measured with method consisted in placing the relation of these salts to curing is pointed out. the dilatometer was merely 20 grams of animal skin (cut A new method of measuring quantitatively the qualitative and it is the purinto 1-cm. edge cubes) in the amount of hydration is given, which is based upon the pose of this work to demondilatometer bottle (120 ml. change in specific gravity of the tissue as measured by strate the extent of hydration capacity). The ground-glass the displacement method. BY this method, as well as in a more quantitative manconnection was then well luby the dilatometric method, it is shown that hydration ner. I n the previous work bricated and inserted in the is different from swelling. only the millimeter contracbottle, care being taken to rid tion of the system was noted. the system of all air bubbles. The apparatus was then placed I n the present work the capillary tubes were accurately caliin a thermostat maintaining a temperature *0.5" C. of the brated before use and the millimeter contraction was changed desired temperature. over into milliliter contraction. By this means the actual I n the previous papers various factors affecting the hy- number of milliliters of liquid compressed by the material dration were discussed and it was shown that hydration and was known. swelling were not parallel effects. It was further pointed Effect of Post-Mortem Action out that, though swelling could be accounted for by the Donnan membrane theory, hydration, a t least to some degree, It was shown by McLaughlin (1) that post-mortem action must be considered as due to residual valence forces. It was radically affected the ability of fresh animal skin to swell, further shown that the hydration as measured by the dilato- This swelling, often termed "hydration," was measured by the weight-gain method. The effect of post-mortem action Received September 27, 1930. Presented before the Division of upon the hydration of fresh calfskin is shown in Figure 1. Leather and Gelatin Chemistry at the 80th Meeting of the American ChemiIt is readily seen, first, that there is a drastic change in the cal Society, Cincinnati, Ohio, September 8 t o 12, 1930. Barretr and Co. Leather Research Fellow, Lehigh University. potential ability of the skin to hydrate from 3 per cent in
P
