1550
J. R . PARTINOTON AND H. H. NEVILLE
The properties of these two salts have been determined in two different mixtures of water and methanol, the results in the 50:50 weight per cent mixture being given in table 2, and those for the 75 weight per cent water and 25 weight per cent methanol mixture being shown in table 3. GENERAL OBSERVATIONS
In the case of the sulfamate solutions, the trend of the conductivities seems roughly to follow that of the temperatures of measurement, despite the fact that the concentration: are constantly increased. This seems to indicate again the great influence of viscosity upon ionic mobilities. In the solvent mixture containing 75 per cent water and 25 per cent methanol, the zinc salts appear to be more soluble than those of magnesium, but the difference in molecular weights makes the molal solubilities similar. For the methanesulfonates, an increase in the water content of the solvent increases the conductivity a t the higher temperatures by from two- to three-fold, but this appears to be the result of increased solubility rather than of any enhancement of ionic mobilities. Increase of water content also serves to diminish the solubility a t low temperatures. It is interesting to notice also that in the 50:50 solvent mixture, the change in conductivity with change in concentration is relatively small a t -40°C. and, moreover, that the conductivities themselves are almost the same for the two salts a t comparable weight concentrations in the same temperature region. REFERENCES (1) B E R T H O UAD,,: Helv. Chim. Acta 12, 859 (1929). (2) K I N GG. , B . , AND HOOPER, J. F . : J. Phys. Chem. 46,938-42 (1941). (3) PAQUETTE, R . G . , LINGAFELTER, E . C . , AND TARTAR, H . V . : J. Am. Chem. SOC.66, 686-92 (1943). (4) P E R R YJ. , H . : Chemical Engineer's Handbook, 2nd edition, p. 2613. McGraw-Hill Book Company, Inc., New York (1941). (5) SCHMELZLE, A . F . , A N D WESTFALL,J . E . : J. Phys. Chem. 48, 165-8 (1944).
ORTHOBARIC DENSITIES AND SURFACE TENSION OF CARBONYL SULFIDE J. R . PARTIKGTON
AXD
H. H. NEVILLE
Chemislry Department, Queen X a i y College, Cnicersily of London, London E . 1 , England Received November d d , 1960
The density and surface tension of liquid carbonyl sulfide have been measured a t a few isolated temperatures only,-the surface tension by one observer, the density by two. A supply of pure carbonyl sulfide being a t hand, it was considered that a redetermination of these fundamental properties over as wide a range of temperature as possible would be of value. Stock and Kuss (7) reported the liquid density a t -87OC. as 1.24 g./cc. More recently Pearson, Robinson, and Trotter (6) measured the density a t three
DENSITY AKD SURFACE TENSION OF CARBONYL SULFIDE
1551
temperatures near room temperature. Their values were: 1.073 g./cc. a t O.O"C., 1.028 g./cc. a t 17.0°C., and 0.986 g./cc. a t 32.2"C. Orthobaric densities have not been determined, but the critical temperature was reported by Ilosvay (3) as 105"C., and the same value was obtained by Hempel (2). In the present work the liquid density was determined between -100" and +lOO"C., with orthobaric densities above +25"C., and the surface tension from -100' to +40°C. Carbonyl sulfide was prepared from Bender's salt (1) by the action of dilute acid. The gas was passed through a bottle a t 0°C. to retain alcohol vapor, through 30 per cent sodium hydroxide and then concentrated sulfuric acid, and through a trap at -55°C. to remove final traces of alcohol; it was then condensed in liquid air. After thorough evacuation it was distilled through a column of phosphorus pentoxide, head and tail fractions being rejected. Finally it was redistilled into storage bulbs, head and tail fractions being again rejected. THE DENSITY MEASUREMENTS
The temperature range was covered in two sections: namely, below and above 25%. Four pycnometers were used, shaped like thermometers but with thickwalled bulbs. In the lower range two of these were used alternately to determine the density of the liquid phase. The correction for the mass of carbonyl sulfide in the vapor phase was calculated from the vapor pressure. In the higher temperature range the other two pycnometers were used in conjunction to determine the densities of both phases a t each temperature. The tubes were selected from a large number of pieces after testing the uniformity of the bore. Those finally selected had a bore constant within 0.005 mm. over the effective portion, which corresponds to a change of 0.02 mm. in the length of a 5-mm. thread of mercury, and with the bulb and 5 cm. of bore occupied by liquid, this represents a maximum error in the total volume of about 1 part in 3000. The volume of the bulb up t o a reference mark on the stem was determined by filling with mercury and weighing. The difference between the mercury and carbonyl sulfide menisci was allowed for by adding two-thirds of the radius of the tube t o the height of the mercury. The pycnometers were sealed to the vacuum line, thoroughly exhausted, filled with a suitable volume of liquid carbonyl sulfide, and then sealed off. They were weighed, and at the end of the determination broken and weighed again, the weight of air included in the second case being deducted. The dimensions of the pycnometers were as follows:
Material Bore, cm Volume per centimeter of bore, c c Volunie up t o reference mark, cc Temperature, "C Length of bore from mark to top, cm Weight of COS, g
I
A
'
Soda glass
0 0317 0 7810 1 0055
I
B
Soda glass 0.208 0.0340 0.5153 20.7 19.82 0.5871
C
D
Pyrex Pyrex 0.218 0.198 0.0313 0,0301 0.4980 0.6995 20.3 21.3 20.14 15.86 0.5920 0.8872
1552
J. R . PARTINGTON AND H. H. NEVILLE
The pycnometers were completely immersed, two a t a time, in a bath which contained alcohol cooled with solid carbon dioxide or liquid air in the lowtemperature range, and liquid paraffin heated with a small flame in the hightemperature range. The containers were, respectively, an unsilvered Dewar flask and a glass cylinder. The temperature was measured with three thermometers: ( 1 ) a mercury thermometer reading from - 10" to +,llO"C. in degrees, (2)a mercury thermometer reading from 0" t o +5O"C. in tenths of a degree, and (3) a pentane thermomeeter reading from - 100' to +30°C. in tenths of a degree. These thermometers TABLE 1 Calibration of thermometers ASSUMED TRUE IEYPLPATURE
1. . . . . . . . . . . . .
1 ............
I
99.9
'C. 99.7
~
j
EPPOP
'C.
+0.2
(vapor pressure of water = 755 mm.) -0.1
0.0
-0.1
(melting ice)
2. . . . . . . . . . . .
50.0
2. . . . . . . . . . . .
0.0
3. . . . . . . . . . . .
+0.2
3. . . . . . . . . . . .
-60.0
3. . . . . . . . . . . .
.-90.0
3.. . . . . . . . . . .
-100.0
50.0 (thermometer indicating 50.1') 0.0 (melting ice) 0.0 (melting ice) -60.2 (COS vapor pressure = 456 mm.) -90.3 :COS vapor pressure = 73 mm.; CO1 vapor pressure = 382 mm.) -100.4 (COS vapor pressure = 33 mm.; COS vapor pressure = 95.5 mm.)
0.0
0.0
+0.2
-0.2 -0.3 -0.4
were checked a t the boiling and freezing points of water, and by comparison with vapor pressure thermometers containing carbonyl sulfide and carbon dioxide, the latter giving also a check on the purity of the carbonyl sulfide. These thermometer comparisons were carried out in the same baths and under otherwise identical conditions as were the actual density measurements. The results are given in table 1. The critical phenomena were first observed with rising and falling temperatures. The latter were the more distinct. The critical temperature was 102.2"C. =k0.2"with both pycnometers. The densities were then determined with falling temperature (see table 2). Here h in column 3 represents the height in centimeters of the liquid column in each pycnometer above the reference mark. The vapor pressures of carbonyl sulfide in column 4 were used to calculate the vapor den-
DENSITY AND SURFACE TENSION OF CARBONYL SULFIDE
1553
TABLE Densill
(4)
f
2 carbonyl aulflde (7)
(5)
'C.
-99.5 -88.2 -80.0 -72.3 -65.5 -58.3 -52.9 -46.2 -39.1 -34.3 -30.4 -23.3 -16.0 -9.7 -1.7 +3.6 +7.9 +16.3 +21.6 +29.8 +36.2
Cm.
A
B
0,334 0.375 1.04: 0.942 1.659 1.343 2.044 1.946 2.779 2.481 3.365 3.118 4.208 3.784 5.455 4.815 6.257 5.760 7.507 1.932
C
2.280
B
2.155 2.460 2,552 2.803 2.918 3.140 3.514 3.639 4.123 4.194 4.729 4.577 5.326 4.864 8.113 7.019 12.965 9.312 18.231 13.510
D A D A D
A
D A D A D A
D A
D A D A
C +44.1 +51.7 +59.8 +66.3
B C B C B C
B C
+75.1
B C
+85.4
B C
+93,5 +99,8 +100.9
B C B C B C
~-
'PESEURE
pu
,l1m.
p./CC.
0.32 0.47 0.66 0.85 1.09 1.49 1.' 72 2.05 2.68 3.48 4.38 5.69 6.71 7.65 9.88 11.35
(9)
PI
VAPOP
MEAN
(CALCU-
DENS1I Y
LATED) E./CC.
K./cC.
0.010 0.012 0.015 0.018 0.020 0,025 0.030
1.274 1.251 1.238 1.220 1.208 1.196 1,188 1.168 1.155 1.142 1.131 1.113 1.097 1.083 1.052 1.040 1.023 1.004 0.981
1.272 1.253 1,238 1.224 1.210 1.195 1.184 1.168 1.152 1.141 1,131 1.113 1.093 1.077 1.054 1.039 1.026 1.000 0.983
0.050
0.956
0.956
0
0.503
0.058
0.936
0.936
0
0.497
0.070
0.907
0.908
-0.001
0.489
0.082
0.878
0.881
-0.003
0.480
0.096
0.841
0.469
0.110
0.804
0.457
0.142
0.762
0.452
0.215
0.691
0.453
0.269
0.606
0.418
0.371
0.523
0.441
0.373
0.499
0.436
0.0012 0.0017 0.0023 0.0028 0.004 0.005 0.006
0.006 0.008
+W.002 -0.002 0
-0.004 -0.002 +0.001
+O ,004 0
+O ,003 +0.001 0 0
+O ,004 +0.006 -0.002 ,001 -0.003 +0.004 -0.002
+o
sity, po, in the next column up to 21.6"C.,and were taken from Stock and Kuss (7) up t o -52.9"C., and from the International Critical Tables (4)between this and 21.6"C. In column 6 the liquid densities p l , calculated from the observations,
1554
J.
R. PARTINGTON AND H. H. NEVILLE
are given. Above 21.6"C. both pv and pl are calculated from simultaneous observations on two pycnometers. The expansion of the pycnometers has been taken for soda into account, using the coefficients of cubical expansion (2.55 X glass and 9 x for Pyrex glass (5)). 1.3, 1.3
IO.
0.94I
FIQ.1. Density of
liquid carbonyl sulfide from -100°C. to +50°C. 0, present work; A, Stock and Kuss.
0 , Pearson, Robinson, and Trotter;
30.
::\
. I S5 .
-io0
-m
-40
-10
-20
o
+PO
t40
FIG.2 . Curve of orthobaric densities of carbonyl sulfide FIG.3. Surface tension of liquid carbonyl sulfide from -100°C. to +40°C. 0, present work; 0 , Pearson, Robinson, and Trotter
By applying the method of least squares to the liquid densities it was found that these could be represented up to about 50°C. by the equation pi =
1.049 - 0.0029t
- 6.76 X
10-'t2
and column 7 shows the densities calculated from this at each temperature. In column 8 the differences between observed and calculated densities are given. Column 9 gives the mean densities used in plotting the rectilinear diameter of the curve of orthobaric densities. This curve is shown in figure 2, while in figure 1 the liquid density is shown from - 100" to 50°C.
+
1555
DESSITY AND SURFACE TENSION OF CARBONYL SULFIDE THE MEASUREMENTS OF SURFACE TENSION
TKOPyrex capillary tubes were selected after testing the uniformity of the bore. Owing to the shorter effective length required, as compared with the pycnometer tubes, greater degree of uniformity was possible. Those selected were such that a thread of mercury about 0.5 cm. long had the same length within 0.001 cm. over the effective portion, which implies that the radius of about 0.02 cm. was constant t o within about O.ooOo2 cm. The circularity of the bore was tested by measuring two perpendicular diameters a t each end with a travelling microscope, and the actual bore mas then determined by filling the effective portion with mercury, measuring the length of the mercury thread, and weighing the mercury. TABLE 3 Surface tension of carbonvl sulfide I
I
'
h
P"
im.
g./cc.
PI
I
'C.
-97.5 -87.6 -76.0 -69.5 -56.5 -49.5 -40.1 -29.1 -19.3 -6.1 +2.2 f11.3 +18.7 +29.0
+40.1
, 1
1
1 ~
1 1
1 l
1 658 1 636 1 628 1 539 1 495 1 409 1 359 1 206 1 138 o 971 0 879 0 782 0 683 0 608 0 509
0.001 0.001 0.002 0.003 0.005 0.006 0.009 0.013 0.017 0,022 0.027 0,047 0.064
f./U
1.268 1.251 1.230 1.218 1.191 1,176 1.155 1.128 1.102 1.066 1.043 1.015
0,992 0.959 0 922
I
I
Y
1
dyneslcm.
27.05 26.31 25.73 24.06 22.84 21.20 20.03 17.31 15.88 13.00 11.43 9.80 8.28 6.93 5.41
The two capillaries finally selected had radii of 0.02119 cm. and 0.10350 cm. They were rigidly connected together, parallel to each other, by fusion to a small glass web near the top. They were cleaned by drawing through them hot aqua regia, followed by distilled water and steam. They were then placed in an outer tube of Pyrex, of 1.8 cm. bore and 0.25 mm. wall thickness, which was connected to the vacuum line. hfter evacuation and filling with about 2 cc. of liquid carbonyl sulfide, the tube was sealed off and measurements begun. The same baths and thermometers were used as described in the previous section, but in this case the results were obtained with rising temperature, in order to secure a falling meniscus. Table 3 shows the difference in height, h cm., between the menisci in the two tubes at yarious temperatures. The vapor densities, pL,were obtained in the same way as in the previous section, and the liquid densities, pi, were calculated from the empirical equation there given. The surface
1556
J. R. PARTINGTON AND H.
n.
NEVILLE
tension, 7 , in dynes per centimeter, was obtained from the expression: 7 =
+
gTirz(p( - Po)(% 6(% TI)
-
Ti
-
h)
which is obtained from the simple equation for capillary rise:
2 m =
&(PC
- PJh
by considering two capillaries of radii TI and ~ 2 and , allowing for the volume of the meniscus by adding one-third of the radius t o the height of the column, on the assumption that the meniscus is approximately hemispherical. The value of g has been taken as 981.18 (5). Figure 3 shows the variation of surface tension with temperature; a smooth curve has been drawn through the points. The determinations were abandoned after 4O.l0C., owing to bursting of the tube. DISCUSSION
The liquid densities found by Pearson, Robinson, and Trotter are somewhat higher than those found in the present work. This is probably due to the fact that these observers have apparently not taken into account the mass of the vapor phase. It is not possible t o adjust their values, owing to lack of information on the dimensions of their pycnometers. Because of the high vapor pressure (about 10 atm. a t room temperature) the mass of the vapor is not negligible unless the volume of the vapor space is unusually small. For example, taking pycnometer D at 16.3"C., and neglecting the mass of the vapor, the density appears to be 1.015 instead of 1.004. The curve of orthobaric densities (figure 2) confirms the observed critical point a t 102.2"C. f 0.2", a value which is a little lower than the accepted value, 105'C. The two surface tension measurements of Pearson, Robinson, and Trotter are also somewhat higher than ours, but the difference is about the same as the density difference, so that surface tension measurements may be taken to agree. The parachor calculated from the present results is 108.3 a t O'C., as compared with the theoretical value of 119.7. SUMMARY
1. The liquid density of carbonyl sulfide has been determined between and +100"C. The empirical equation p1
=
1.049
- 0.0029t - 6.76 X
- 100"
10-'t2
represents the experimental results from - 100" t o +50°C. 2. Orthobaric densities have been determined from 30°C. to the critical point, which is found t o be 102.2"C. f 0.2". 3. The surface tension of carbonyl sulfide has been determined between - 100" and +40"C.
COAGULATION O F HYDROPHOBIC BOLS. I
1557
The authors are indebted t o the Chemical Society, London, and to the Central Research Fund of London University for grants which have helped to defray the cost of the apparatus used in this investigation. REFERENCES BENDER,C: Ann. 148, 137 (1868). HEMPEL, W.:Z. angew. Chem. 14, 865 (1901). L.: Bull. soc. chim. Belg. 37, 294 (1882). ILOSVAY, Znternational Critical Tables, Vol. 111, p. 231. McGraw-Hill Book Company, Inc., New York (1928). (5) KAYE,G. W. C., AND LABY,T. H.: Tablas of Physical and Chemical Constants, 10th edition. Longmans, Green and Company, London (1918). (6) PEARSON, T. G., ROBIXJOX, P. L., AND TROTTER, J.: J. Chem. SOC. 1931,660. ( 7 ) STOCK,A., A N D KUTRS, E.: Ber. 60,159 (1917).
(1) (2) (3) (4)
COAGULATION OF HYDROPHOBIC SOLS I N STATU
NASCENDI. I DETERM1N;ATION O F COAGULATION VALUES B . TEZAK, E. MATIJEVIC,
AND
K. SCHULZ
Laboratory of Physical Chemzstry, Faculty of Science, University of Zagreb, Zagreb, Yugoslavia Received October 6 , 1950
The investigations of Weiser (20), O d h (9), Balarew (l),Hahn (j),Kolthoff ( 7 ) ,Traube (15), Fricke (1),Feitknecht (3), Teiak (12), and others have shown that the formation of heteropolar precipitates of low solubility from aqueous solution proceeds through two distinct stages : ( 1 ) the formation of primary particles and (2) their agglomeration into secondary structures. This second stage may be an oriented aggregation of small “blocks” in the sense of Smekal, where some “vectorial” forces evert a specific influence on their regular overgrowth, or a process with all characteristics of the coagulation. However, it must be pointed out that the processes of direct ionic growth of the primary particles cannot be neglected, especially in the region of the increased “ordinary” or “complex” solubility, that is, in media where the concentrations of the precipitation components are close to the solubility product, or where one of the precipitation components is in such excess that its solubility effect becomes preponderant. In other regions where the initial concentrations of the precipitating ions are more than ten times larger than the normal solubility, the formation of the amicronic or rolloidal primary particles is almost instantaneous (2), while the stability of the primary particles in the case of an excess of one of the precipitating ions is usually very pronounced (8). Of course, with such systems, e.g., silver halides in statu nascendi, it is possible t o observe all the coagulation effects of neutral electrolytes which are found
