SPECIFIC HEATS OF SODIUM CHLORIDE SOLUTIONS
755
3. The marked ion antagonism which occurs when an arsenic trisulfide sol is coagulated by mixtures of potassium chloride and barium chloride was verificd. 4. An electrophoretic study was made of the systems, and the mobilities of the particles at the coagulating concentrations of the electrolyte mixtures were determined. 5 . It was found that as the concentration of potassium chloride, in a coagulating mixture with barium chloride or with chromium chloride, was increased, the critical mobilities likewise increased, 6. The results were discussed and explanations for the various behaviors were proposed. REFEREXCES (1) FREUNDLICH A X D SCHOLZ: Kolloid-Beihefte 16, 267 (1922). (2) H A Z E LJ: Phys. Chem 46, 736 (1911)
(3) KRCYTA X D VAK DER M'ILLIGEX:Proc Roy. h a d . Amsterdam 29, 484 (1926). J. Chem. Soc 67, 67 (1895). (4) L I X D E R A NPICTOX: D ( 5 ) WASXOW: Kolloid-Beiheftc 60, 367 (1939). (6) WEISER: J. Phys. Cheni. 30, 1531 (1926) (7) WEISER:Inorganzc CoUozd Chemzstry, Yol. 111. John Wiley and Sons, Inc., K e w York (1938). (8) WEISERAND MILLIGAX:J. Am. Chem. Soc. 62,1921 (1940).
THE SPECIFIC HEATS OF SOME AQUEOUS SOLUTIOSS OF SODIUM ASD POTASSIUM CHLORIDES AT SEVERAL TEMPERATURES. I11
RESULTS FOR DILUTE SODIUM CHLORIDE SOLUTIONS AT 25°C. C. B. HESS Department of Chemzstry, The C'nacerszty of Rochester, Rochester, XezL. Yorli'
Recezved A p r i l 18, 2940
I n the adiabatic twin calorimeter described earlier (4), the calorimeter covers were in direct contact with the jacket water and thus presumably were a t jacket temperature. Since the temperature in the two calorimeters is seldom, if ever, the same, a temperature head might exist between the covers and the solutions in the calorimeters which might lead to different condensation effects in the two calorimeters. If the respective covers could be kept at the temperatures of the solutions in the calorimeters, such condensation effects would probably be eliminated. I n this Present address: E. I. du Pont de Nemours and Company, Inc., R. & H. Chemicals Department, Xiagara Falls, New York.
756
C.
E. HESS
paper will be found a brief report of an attempt which has been made to attain this end; the experimental results are limited to dilute sodium chloride solutions and a single dilute solution of lithium chloride. Although there is some question as to the desirability of such a construction, it seems well to publish the results now, especially since it has been necessary to discontinue this series of researches. APPARATUS AND MATERIALS
To attain the end just mentioned, an entirely new apparatus was constructed, having the upper portions of the calorimeters and their covers
FIG.1. Calorimeter assembly (A) and detail of one calorimeter (B)
thermally isolated from the jacket water. This was accomplished by constructing a submarine cap A (figure 1, A and B) of thin, ground, highly polished Monel metal, having two spun-copper collars (K), soldered into the bottom. These collars carried the internally threaded calorimeter rings made to fit the threaded rings which were cemented to the Dewar flasks. The calorimeter covers were of Monel metal insulated from the submarine cap by t in. rubber gaskets (X) ;these parts were held in place by means of studs and wing nuts, which are not shown. A heavier sheet of Monel metal served as the submarine cap cover, being held down on a rubber gasket (V) by means of studs and wing nuts. The cover had three
SPECIFIC HEATS OF SODIUM CHLORIDE SOLUTIONS
757
chimneys attached to it: the outer two carried the calorimeter stirrers, while the large central one (D) housed the heater and thermel connections to their outer leads. The whole cap was suspended from the heavy jacket cover. In preliminary runs the Dewar flasks were of heavy Pyrex glass and had shoulders as indicated in figure 1, A ; these were found to produce large lags, so were replaced by thin-walled soft-glass Dewar flasks of 500-cc. capacity of the shape indicated in figure 1, B. The flasks were snugly fitted to the soft-rubber gasket rings L, to restrict evaporation to the space immediately above the liquids. The difference thermel C had twelve junctions and gave a sensitivity of about 0.000074° per millimeter. The adiabatic thermels H and B were of five junctions and gave a sensitivity of approximately 0.00018° per millimeter. The calorimeter heaters and stirrers are not shown in figure 1. Many details will not be touched upon here, as they are on record elsewhere (3). The water and sodium chloride used in this research are believed to be of essentially the same purity as those used earlier. The lithium chloride was twice recrystallized from distilled water and dried overnight in an oven a t 115OC. In all cases the solutions were analyzed by precipitating with silver nitrate and weighing the silver chloride residues; duplicate determinations, which agreed on the average to 0.62 part per thousand, were averaged to give the concentrations listed. PROCEDURE
Few, if any, significant changes were made in the procedure. An effort was made always to charge the tare calorimeter with 430.460 g. (corrected to vacuum basis) of distilled water. I n case the weight departed from this figure by 2 mg. or more, a suitable correction was applied to the observed AG values; in no case did the correction exceed 0.2 mm. Weights of water and solution were brought to the vacuum basis, taking into account the barometric pressure, humidity, and temperature in the room. The fore period was of 10 min. duration, while the heating period, immediately following, was 8 to 10 min. in length, with but one exception. The aft period used in all of the calculations, the results of which are presented in this paper, extended without e;tception from the 36thto the 50th minute. The method of least averages (1) was employed to calculate the equations for the lines of the fore and aft drifts; by inserting in these equations the time (approximately 14.50) when half of the heating period had elapsed, numbers were obtained which when subtracted gave the important AG values. All of the results were also calculated on the basis of a 38- to 48-min. aft period; when so treated, the final values of the specific heat are on the average 0.001 per cent higher than those presented in this paper, and no single determination differed by more than 0.003 per cent. I n the
758
C. B. HESS
water standardizations the longer aft period calculations gave a 20 per cent smaller deviation from the least squares equation, which is one of the principal reasons for presenting the results on the 36- to 50-min. aft period basis. Fourteen water standardizations were made from time to time during the course of the whole research. A least squares equation (W = 435.520 0.0346 AG) was obtained and used in calculating the solution equivalent. The average difference between the experimental and calculated weights in these standardizations was approximately 0.004 per cent, equivalent to nearly 18 mg. of water and 0.5 mm. in AG. The temperature interval was from 24.5" to 25.5"C. Check runs were made, in nearly every case, a t 25.5"to 26.5"C.,but the results of these runs
+
TABLE 1 Summury of the datu f o r sodium chloride solutions
.-,
,-.
BERIEB ?:?E," NUMBER TERMI-
1
j
1 MOLALITY
1
dz
1
AVERAQE VALUE O F T H E !~PECIFIC HEAT' MEAN
1
LINE
1
15' calorres
5
1
3
0.1511
0.3887
0.99846 0.99827 0.99814 0.99793 0.99763 0.99764 0,99734 0.99671 0.99611 0.99549 0.99460 0.99360 0.99109 0.98745
-0.1 0.1 0.1
I
0.3 0.1 0.6 0.1
I
~
1
1
1
-6.81 -20.24
+1.6
-0.3
-0.3 10.0 $0.3 $0.4
I
1 ~
-17.93 -17.11 -16.29 -15.55
are not given here, since in almost every case the AG values were such as would be expected for this interval of temperature. EXPERIMENTAL RESULTS
In table 1 will be found a summary of the data for sodium chloride solutions. Columns 1 and 2 give the order in which the runs were made, Le., four separate runs were made on different portions of a solution of molality 0.01009, then three separate runs were made on different portions of a solution of molality 0.04039, and so on. I n columns 5 and 8 will be found the average values of the specific heat and the corresponding values of a. The 15" calorie is used throughout this paper; the ratio of the 25" calorie to the 15" calorie is taken to be 0.99852.
SPECIFIC HEATS O F SODIUM CHLORIDE SOLUTIOIiS
759
Two runs were made on a lithium chloride solution of molality 0.1480: the average value of the specific heat was 0.99061 ; the average deviation from the mean was 0.1 p.p.t.t.; the average value of Q was - 11.42. DISCUSSIOX O F RESULTS
In figure 2 will be found the values of @ given in column 8 of table 1, plotted versus m* for the ten series above m* = 0.1005. The straight full line, the equation for which is @ = - 19.70 10.00 mi, fits the data plotted quite well, as may be seen from column 7 of table 1, the positive and negative values being equal within 0.1 of a unit for nine of the series (the value for the other exceeded four times the average of the nine); the aver-
+
6 FIG.2. Apparent molal heat capacity (0)of sodium chloride in aqueous solutions a t 25°C.
age departure for these series is less than 0.004 per cent, while the average of the corresponding values in column 6 is about 0.002 per cent; the average departure for all fourteen series is 0.008 per cent. The radii of the circles correspond to 0.001 per cent and the dotted bands on either side of the straight full line to k0.005 per cent. I n this section all percentages refer to the specific-heat values. Relatively little value is attached to the @ values for the first four series, since for these series the averages of the values in both columns 6 and 7 are approximately four times the respective averages for the other series. Furthermore, it is generally agreed by workers in this field that direct specific-heat measurements are of relatively little value in fixing the position of the Q versus mfcurve below mf= 0.1.
760
C. B. HESS
The equation given above is slightly above that given by White (6), who has subjected the data of Hess and Gramkee to a least squares treatment. Curve A at the bottom of figure 2 gives the differencesbetween the two straight lines on a percentage basis. If the equation given above is extrapolated, it is found that curve A passes through a maximum a t m* = 0.7, the percentage difference being 0.025, while a t m+ = 1.0 the percentage difference has fallen slightly below zero. Thus in this range of concentration the average departure of the present equation from that given earlier is less than 0.02 per cent, and in the range of concentration studied the average departure is less than 0.01 per cent. Since the probable error for the earlier work has been placed at 0.02 per cent (table 4 of reference 5) the present results are in entire accord with those presented earlier, the precision of measurement being perhaps three to four times better. White (6) has also calculated a reference curve combining what appeared to be some of the best data in the dilution field and in the field of direct measurements. Curve B gives the difference between this reference curve and the equation for the present data. By combining information given in the last paragraph with curve V of figure 5 of White’s paper, it is possible to get a fairly accurate idea of the percentage differences between the extrapolated equation and the reference curve; suffice it to say here that at mi = 1.0 the percentage difference has again fallen slightly below zero. The average value of CP for the lithium chloride runs is 2.2 calories per degree more positive than the value calculated from the equation given by Gucker and Schminke (Z), which corresponds to a percentage difference of 0.03. White (5), using an apparatus of the type employed by Hess and Gramkee but incorporating some of the features developed in the present research, made four check runs on lithium chloride at a considerably lower molality (0.0492); for these runs the average deviation from the mean is 0.003 per cent and the average value of CP is higher than the value given by Gucker and Schminke’s equation by about half this figure, which is about one-fifth of the over-all precision claimed by him. There is the further point that a t m = 0.1480 the present results for sodium chloride are about 0.04 per cent higher than the reference curve. Finally, it may be said that if the present equation is assumed to hold to mi = 1.0, the average departure from the reference curve would be about 0.04 per cent. All of these facts point to the conclusion that the present results are probably high. Though a definite effort has been made to determine the reason for such a departure, no satisfactory solution to the problem has been found, It is recognized that to fix the position of the curve with more certainty would require more determinations over a wider range of concentration. In the range of concentration studied, the present results are on the average within 0.01 per cent of those presented earlier and within 0.02 per cent of the reference curve.
HOPCALITE CATALYSTS
76 1
SUMMARY
A brief description is given of an adiabatic twin calorimeter having the calorimeter covers in thermal contact with the liquids in the calorimeters. The results of thirty-nine runs on relatively dilute sodiufn chloride solutions at 25°C. are given. Compared with the first work from this laboratory, some improvement in precision of measurement seems to have been attained, but the results are somewhat higher than those obtained earlier. The experimental part of this work was carried out under the supervision of Dr. Arthur A. Sunier; the final calculations and the preparation of this brief report are due to him. Grateful acknowledgment of these facts is here made. REFERENCES
(1) DANIELS:Mathematical PrepaTationfor Physical Chemistry, pp. 235-7. McGrawHill Book Company, Inc., New York (1928). (2) GVCKER AND SCRMINKE: J. Am. Chem. SOC.64, 1358 (1932). (3) HESS: Thesis, University of Rochester Library, 1935. (4) HESSAND GRAMKEE: J. Phys. Chem. 44,483 (1940). (5) WHITE: J. Am. Chem. SOC.68, 1615 (1936). (6) WHITE: J. Phys. Chem. 44,494 (1940).
T H E PHYSICAL CHEMISTRY OF HOPCALITE CATALYSTS' E. C. PITZER2 AND J. C. W. FRAZER
Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland Received M a y 10, 1940 I. INTRODUCTION
The catalytic oxidation of carbon monoxide has been the subject of numerous publications from this Laboratory. Two types of catalysts have been extensively investigated,-the higher oxides of the metals of the first transition group (2, 5, 11, 13, 21) and the chromites of certain bivalent metals (9). The higher oxides of manganese, cobalt, and nickel, when scrupulously pure, are catalysts for this reaction a t temperatures as low as -2O"C., n-hereas the chromites are appreciably active only above 100°C. The purpose of the present investigation was to determine whether a high degree of purity and a fine state of subdivision are the only requisites I .In ahstract of the disseitation which was presented by E . C. Pitzer to the Faculty of The Johns Hopkins 1-niversity in partial fulfilment of the requirements for the degree of Doctor of Philosophy, May, 1939. * Present address: Standard Oil Company of Indiana, Whiting, Indiana.
