JUNE. 1940
I\DVSTRI.IL .4ND ENGINEERING CHEMISTRI
Literature Cited (1) h m a g a t , Comqt. rend., 114, 1093 (18921. (2) A n d r e w , P., P h i l . T r a n s . . 159, 575 (1869). ( 3 ) I b i d . , 178, 53 (1887). (4) Bahlke and K a y , ISD. ESG.CHEU.,24, 291 (1932). ( 5 ) Boomer, Johnson. and Piercey, Can. J . Research, B16, 319. 396 (1938). (6) C a g n i a r d d e l a T o u r , A m . ,21, 127, 178 (1822); 22, 410 (1823'. (7) Cailietet, Cornpt. rend.. 90, 210 (18801. ' (8) C a u b e t , 2. p h y s i k . Chem.. 40, 257 (1902). (9) Cummings, ISD.ESG. CHExr., 23, 900 (1931). (10) Cummings, Stones. and Volante. Ibid.,25, 726 (1933). (11) DeBeck. Petroleum E n g r . . 10, No. 6 . 141 (1939:. (12) D u h e m , J . P h y s . Chem.. 1 , 273 (1897). (13) Faraday, AI., P h i l . T r a n s . . 1845, 153. (14) Foran, h m . Petroleum Inst.. Bzill. 210, 61 (1932). (15) Foran. Trans. Am. Inst. -1Iining .Vet. Engrs., 132, 22 (1939:. (16) Foran and Dixon, Oil Tf'eekly. 93, No. 2, 17 (1939). (17) Frolich, T a u c h , Hogan. and Peer, ISD. ESG. CHEM.,23, 54s (1931). (18) Gilliland a n d Scheeline, I b i d . . 32, 48 (1940). (19) Kamerlingh-Onnes and Keesom, Comrnttn. P h y , . L a b . C-niv. L e i d e n , No. 104b (19081. (20) K a t z . "A. P. I . Drilling and Production Practice", p , 435 (1939). (21) K a t e , T r a n s . S m . I n s t . M i ~ i n gN e t . Erzgrs., 127, 159 (19381. (22) K a t s and Brown, ISD.ESG. C H m r . , 25, 137 (1933). (23) Kats and Hachniuth. Ibid.,29, 1072 (1937). (24) K a t e , \-ink, and D a r i d , Am. Inst. Mining M e t . Engrs.. Tech. Pub. 1114 (1939). (25) K a y . IND.ESG. CHEX, 30, 459 (1938). (26) Ihid.. 32, 353, 358 (1940). (27) K o h n s t s m m and Reeders. d r c h . u & r / u n d . x i . , ,Ser 111.1. 2, 63 (1912). (281 Kuenen, J. P., I M . ,Ser. 11. 5 . 306 (1901 ,
82?
( 2 % Kuenen. C'ommun. P h y s . Lab. C-nit. Leidr,', S o . 4 (1882). (30) I b i d . , No. 13 (1E04). (311 Iiuenen, P h i l . X a g . . 40, 173 (1895). (321 I b i d . , 44, 174 (18971. (331 Kuenen, Proc. Roy. SOC.Edinburgh, 21, 433 (1899). (34 1 Kuenen, "Yerdampfung und Verfliissigung von Gemischen", 1906. (351 Kuenen and Clark. Commlm. Phys. L a b . Crrio. Leiden, No. 150b (1917). ( 3 6 Lacey, -1m. Petroleum Inat., Bi(11.210, 65 (1932)). (378 Lindsly, U. S. Bur. Mines, Tech. P a p e r 554 (1933); K e p t . Inaestigations 3212 (1933). ( 3 8 Xysen-ander, Sage, and Lacey, I s u . C S G . C'HELI., 32, 118 (1940). (39' P a t t e n and Ivey. Oil T e e k l y . 92, Nu. 1. 20 (193s). (40) Roess. J . I / d . Petrolcftm Tech.. 22, 665 (1936). (41" Roozeboom. "Die heterogenen Gleichgemichte 11", Brunsw-ick, German>-,Friedrich Tieweg u n d Sohn, 1904. ( 4 2 1 Sage. Schaafsma, and Lacey, ISD.Eso. CHEM., 26, 214 (1934); . h i . Petroleum Inst., Bull. 212, 119 (19331. (4.31 Scheeline and Gilliland, ISD.ESG.CHEM.,31, I050 (1939). (441 Schroer, Z. p h y s i k . Chem.. 142, 365 (1929). (45) Souders, Selheimer, and Brown, Ibid.. 24, 517 (1932). (46, Taylor, Wald, Sage. and Lacey, Oil Gas J . , 38, S o . 1 3 , 46 (1939). ( 4 7 ) Travers and Usher, Proc. Ro,y. Soc. (London), 78A, 247 (1906). (48, Tershaffelt. Commun. P h y s . Lab. Cniv. Leiderr, X o . 47 (1899). (491 Villard. J . phys.. 5, 453 (1896). (501 \Vaals, van der, a r c h . nderland. sci., Ser. 11, 15, 126 (19101. (51 1 Waals, van der. "Kontinuitiit der gasformigen und fliissigen Zustandes". 1881. ( 5 2 ! Young. Sei. Proc. R o y . Dublin Soc., 12, 374 (191Oi. (531 Young, "Stoichiometry", N e x l-ork. Longmans, Green and co.. 1908. c.541 Zernike. .?rch. & e r / a n d . sci.. Ser. 111.4. 4 , 7 4 (1918..
Fine Particle Suspensions in
Organic Liquids
c. R. BLoofilQGIST AND R. S. SHUT" Battelle Memorial Institute, Columbus, Ohio
The sedimentation volumes of glass spheres, 5 to 15 microns in diameter, were determined in water and in a series of organic liquids. The sedimentation volumes in the organic liquids are identical with that in water or approach this volume as a minimum, as the system is dried more and more intensively. Flocculation of the particles causes the increase from the minimum value. The presence of water dissolved in the liquid and adsorbed on the particles produces this flocculation. The interfacial tension of the organic liquid against water is indicative of the tendency towards flocculation and the difficulty with which the minimum value may be attained. In some cases the sedimentation volume is proportional to the water content of the organic liquid. and in others the liquid must be nearly saturated before flocculation will take place.
T
HE phenomena of setiiment'ation and agglomeration are of vital importance in many manufacturing processes, particularly to the paint and printing ink industries. Agglomeration of pigment particles affects settling and flonproperties of the paint. as well as such factors as gloss, permeability, and durability of the film. For example, the control of flocculation of dispersion is of utmost importance in the formulation of coating compositions. A high degree of dispersion of pigment particles gives improved flon- and gloss which are desirable in certain enamels. Flocculation of pigment particles which induces false bodying or reduced flow in paints is desirable i n flat wall and met,al protective
compositions to permit uniform and complete coverage of the surfaces with one coat. A high degree of dispersion results in a hard cake formation of the pigments on settling, which is difficult to redisperse. On the other hand, flocculated pigments settle to a soft cake which is easily redispersed. It is evident, therefore, that a compromise between the two extremes of flocculation and dispersion must be made in pract,ice to formulate usable compositions. A suspension such as a paint is a complex syst'em consisting of a number of solid and liquid phases, and it is almost impossible to determine the effect of a single substance in the mixture. On the other hand, the behavior of glass spheres
VOL. 32, NO. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
828
aedimenting in pure organic liquids is subject to relatively few variables. Glass spheres present a smooth surface and may be expected to he free of minute cracks and imperfections, and glass is a relatively inert material which should not react a p preciably with the liquids in contact with it. Since i t is possible to determine the diameters of the particles with fair precision, the actual surface area of the particles may he computed with a much higher degree of accuracy than can be obtained with irregularly shaped particles. There are several other advantages inherent in the use of glass spheres: They are readily wetted by most liquids; they may be readily cleaned and re-uaed; the particles have no tendency to disintegrate; and they are more amenable to mathematical and theoretical analysis.
type of results obtained. The polarity and dielectric constants of the liquids appear to have an inffuence on the tendency to produce large final volumes. Many exceptions are found, however, and i t is evident that these are not the only factors involved. The existence of relatively thick lyospheres has been postulated hut not verified. Dilatancy, thixotropy, and sedimentation volumes are undoubtedly related, but not aa cause and effect. None of the explanations enable us to predict the behavior of even a single substance in a series of liquids, for no general rule has been put forward for which some exception cannot he found.
Determination of Sedimentation Volumes
spheres were-separated in& fractions o r nearly uniform'size by average Size given. In 2he ex riments to he descrihed, the 15.2-micron fraction was used nngss otherwise stated. A photomicrograph of the particles in the 7.2-micron size fraction is shown in Figure 1. The sedimentation volumes were determined in the followina cylinder was shaken by hand until the particles were thoroughly dispersed. They were allowed to stand overnight, and the volume of the settled particles was measured the next day. In practically every case the sedimentation was complete overnight, but the cylinders were allowed to stand another 24 hours and the final volumes read again. The second value was taken FlGORE
1.
7.2-MlcRoN SIZE FEACTION GUM SPHERES
OF
The volume occupied by the particles of a suspension after settling is called the "sedimentation volume". With nonreactive particles in pure liquids there is no reason for expecting the final volume after complete settling to vary from liquid to liquid. The results obtained in the liquids tested indicate that it does not vary and that the minimum sedimentation volume nearly corresponds to the closest packing phssihle. When the final volume in any liquid is greater than this minimum, as it frequently is, it is due to the presence of an impurity usually water, dissolved in the liquid and adsorbed on the particles. Since the sedimentation volume is a measure of the degree of flocculation of the particles, the effects produced by the presence of water may point to applications of this phenomenon in the preparation and investigation of pigment-vehicle systems. From a study of the sedimcntation volumes of talc and graphite in a large number of organic liquids, Ostwald and Haller (11)concluded that there is an inverse relation hetwcen the sedimentation volume and the dielectric constant of the Liquid. They ascribed the variation of the sedimentation volume to the binding of a layer of liquid around the particles (lyosorption). Von Buzigh (3) studied quartz suspensions and established a relation between adhesion of the particles to one another (adherence capacity) and sedimentation volumes. Ryan, Harkins, and Gans (8, 18) found that intensive drying decreased the sedimentation volume of inorganic pigments in organic liquids, hut there was no iudication that the volumes were approaching a definite minimum. They believed that the polarity of the liquid was au important factor. Freundlich and co-workers (6, 6 ) showed a correlation between close packing or small sedimentation volume and dilatancy and also between loose packing and thixotropy of pastea. Williamson and Heckert (16) and Akamatsu (1) also carried out investigations along these lines. Although the previous investigators worked with a wide variety of systems, they are in fairly close agreement as to the
wa8 read to the nearest tenth of a milliliter in all oases. In a few of the li uids in which the final volume of the sediment was extremely%rge, the error in reading the volume was greater, for the up r surface of the sediment was often rather irregular. The vaKes of the sedimentation volumes in the tahles are given in milliliters por gram of glass 80 that all the data may he on a cam arable basis. T%e sedimentation volumes of the 15.2-micron spheres in water and in a number of liquids comD1ctelv miscible with water are given in Table I. TABLE I.
SEDIMENTATION VOIXMES OF 15.2-Mlcao~SPHERES IN WATERAND WATER-MISCIBLE LIQUIDS
Sedimentation Yol. Liquid Sedimentation Vol. Ml./mam Ml./"iam Water 0.73 Ethyl alcohol 0.75 Acetone 0.73 Ethyiene lyool 0.75 =-Propyl alcohol 0.73 Lactia 0.75 Methyl alcohol 0.74 Iaopropyl alcohol 0.78
Lisuid
sei!
Amyl alaohol
Table I1 shows the sedimentation volumes in a series of organic liquids in which water is only slightly soluble. Column 2 gives the final volumes in the liquids saturated with water, column 3 in the same liquids from freshly opened bottles. Since these liquids in some cases were not perfectly anhydrous, the sedimentation volumes given in column 3 are not to be taken as the minimum value obtainable in these liquids.
JUNE. 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
829
proper drying agent was introduced into flask A , and drying VOLUMESOF MICRON SPHERES was continued overnight. The liquid was forced into disTABLE 111. SEDIMENTATION IK NITROBENZENE CONTAINING WATER tilling flask B , sufficient liquid was distilled over to fill the Water
Mole yo 0.0 0.27
Sedimentation 1’01. Ml./gram 0.78 0.90
0.40 0.54
2.08
1.43 1.52 1.91
1.26 1.22 1.66
0.78
Sedimentation Vol. Ml./oram 1.97
Water
M o l e yo 1.10 1.17
2.48 2.77
3.08
TABLEIv. SEDIMEKTATION VOLUMES O F 15.2-MICRON SPHERES I N LIQUIDS CONTAIKING WATER (hlL. PER (2R.SM) Per Cent Saturated:-
7
Liquid Aniline Butyl alcohol Amyl alcohol Benzyl alcohol Ethyl acetate Benzene
0 0.75 0.75
0.75 0.79 0.85 1.18
20
40
0.72
0.75 0.75 0.75 1.00 1.58
0.73 0.73 0.75 0.75 1.67 1.73
60 0.73 0.77 0.77 0.88 2.03 1.85
100 1.48 1.67 2.55 2.17
80 0.98 0.98 1.65 1.28 2.28 2.27
2.33
2.73
T.4BLE 1’. EFFECTOF PARTICLE SIZE ON SEDINENTATIOS VOLCME “edimentation Vol., Ml./GramSize of Nitrobenzene Spheres, Methyl Benzene satd. Dry nitrosatd. with Microns Water alcohol with water benzene water 15 10 7 5
0.73
0.75 0.75 0.78
0.74 0.75 0.76 0.78
2.62 2.90 3.54
...
0.78 0.78 0.82
...
3.25 3.00 3.02
...
The effect of water in an organic liquid on the sedimentation volumes was studied by finding the change in final volume produced by the addition of known amounts of water. Since the solubility of water in nitrobenzene was determined by Davis (4), it was chosen for intensive investigation. With the aid of the solubility data the amount of water in a nearly saturated solution can be calculated by observing the critical solution temperature. The nitrobenzene was dried over calcium chloride for several days and then distilled, and the first quarter of the distillate was discarded. The saturated nitrobenzene was prepared, and the water content of this solution was calculated from the critical solution temperature. Mixtures of the dry and saturated liquids were made up to give solutions of known water content. The sedimentation volumes of 10.6-micron glass spheres were determined in these solutions; the data are given in Table 111. Solutions of water in amyl and butyl alcohols, aniline, benzyl alcohol, ethyl acetate, and benzene were investigated in a similar manner. The liquids were dried over a suitable drying agent and distilled just before use. Since solubility data are not available for all of these systems, the concentration of water in each solution is expressed in per cent of saturation rather than in actual water content. The data are given in Table IV. Table V shows the effect of a range of different particle size glass spheres on the sedimentation volume in single liquids. Although it is possible to dry a liquid to zero water content, it was impossible to keep it dry while the graduate cylinder was being charged in the manner described under experimental procedure. This is probably why the higher value was obtained in “dry” benzene (Table IV). Ryan, Harkins, and Gans (12) devised a “dry box” in which they determined sedimentation volumes in the absence of all traces of moisture. Since their procedure was rather elaborate, simpler apparatus which served the same purpose was devised (Figure 2). The carefully dried liquid could be distilled onto the dry glass spheres in the graduate cylinder and the stopper replaced without exposing the liquid to the moist atmosphere. The apparatus was assembled as shown in Figure 2 with the weighed sample of glass in the graduate, and the entire apparatus dried by passing through it a current of air dried over phosphorus pentoxide. This was continued until the small tube of calcium chloride connected to the outlet failed to gain in weight. The liquid which had been standing over the
graduate cylinder, and the stopper was replaced. The graduate cylinder was then removed from the apparatus, shaken to disperse the particles, and allowed to settle. The sedimentation volumes of several sizes of the glass spheres obtained in this manner for benzene and carbon tetrachloride are shown in Table VI. The values obtained in this apparatus (Figure 2) show that smaller sedimentation volumes may be obtained than in similar experiments made without special drying precautions. Since it is definitely known, however, that glass surfaces hold adsorbed gases and moisture tenaciously, it was believed that drying the particles at 110’ C. was insufficient t o remove adsorbed moisture and that this was causing the volumes t o be greater than the minimum. To test this hypothesis, the apparatus shown in Figure 3 was constructed. The sample of spheres could be heated in a vacuum to drive off the adsorbed moisture, and the dry liquid could be distilled onto the spheres without opening the apparatus to the atmosphere. The glass was heated for several days a t 400” to 425” C. a t a pressure of about 1 mm. of mercury. The values for determinations made with two sizes of the spheres in benzene are shown in Table VII. The final volumes obtained are only a little higher than the minimum values, and this minimum is approached as the period of evacuation is increased. Although it is not evident from the data in the tables, the appearance and behavior of the settled particles differed in the various liquids. If the final volumes were small, the particles, after shaking, formed a uniform white suspension which gradually settled and left a clear supernatant liquid. The rate of settling depended on the size of the particles and the density and viscosity of the liquid, but in every case each particle appeared to act independently of the others. The sedimented particles formed a rather hard compact mass which could be redispersed only after vigorous shaking. TABLE VI. SEDIMENTATION VOLUMESIN DRYAPPARATUS (ML. PER GRAM) Size of spheres, microns 15.2 10.6 7.2 5.2 In benzene 1.03 1.02 1..08 ... In CCld ... 0.92 0.99 1.03 In air In water
...
0.76 0.73
I
.
...
0.84
0.78
, . .
.
TABLEVII. SEDIMENTATION VOLUMESIN BENZENE IN VACUUM
--
APPARATUS
--15.2-Micron Hrs. heated and evacuated
SpheresSedimentation vol., ml./g.
50
0.79
..
a
...
0 .‘73a
7.2-Micron Spheres--
Hra. heated and evacuated
Sedimentation vol., ml./g.
48 60 100
0.94 0.90 0.84 0.780
...
Aa obtained in water. ~
~~~~
If the final volumes were large, the particles flocculated immediately and it was not possible t o obtain a uniform suspension. The floccules were sometimes large enough t o be seen, and settled rapidly at first and then more slowly. After the settling had progressed until the floccules were in contact, the sediment appeared to be further compressed into a smaller volume by its own weight. This compressional settling continued for as much as 24 hours, and gentle tapping or vibration caused the volume of the sedimented particles to diminish even more. The particles settling in the flocculating liquids were translucent and gelatinous in appearance and resembled freshly precipitated aluminum hydroxide. Even after com-
INDUSTRIAL A S D ENGINEERING CHEMISTRY
830
VOL. 32, NO. 6
plete settling, inverting the tube once or twice was sufficient to resuspend the floccules. Long continued and vigorous shaking tended to break up the floccules, but as soon as the shaking was stopped the particles settled as before.
In some liquids the increase in the sedimentation volume is proportional to the amount of water present and in others a concentration of water approaching the saturation point must be attained before flocculation occurs. The relative ease with which the minimum value for the sedimentation volume in a pure liquid may be obtained also depends on the nature of the liquid, but in every case tried, it approaches the minimum the more intensively the liquid is dried. The actual amount of water present, either per gram of glass or per gram of liquid, does not have any direct relation to the increase in the sediMERCURY SEAL mentation volume, for it depends only on the per cent of saturation. Hence liquids which dissolve only a small amount of water are more profoundly affected by traces of water. Although it is true that the sedimentation volumes are large only if water is present in the system, the converse does not always hold, for a small final volume does not imply that the susTU DRYING pending liquid is free of water or other impurities. TRAIN For example, the sedimentation volumes in aniline and alcohols are small even when the liquid contains considerable water. However, none of /-MERCURY these facts invalidate the conclusions expressed in the previous paragraph, but it must be em. phasized that they do not work both ways. SEDIMENTATION VOLVMESIN FIGURE 2. APPARATUSFOR DETERMINING The presence of water in an organic liquid in MOISTURE-FREE ATMOSPHERE which it is only partially miscible causes the sedimentation volume to increase from the minimum value, but the effect produced varies from liquid to Microscopic examination of the floccules indicated that the liquid. The ease with which the minimum value may spheres were being held together in clusters and filaments. be reached is also different in different liquids. This suggests Individual particles were not free to move and were held t o that the variations in behavior are due to some physical each other very rigidly. Since these clusters of particles or chemical properties of the system water-organic liqwere irregularly shaped, large voids were left between the uid. Since adsorption of the water will take place a t the floccules after settling, and only by changing the shapes of the floccules could the degree of settling be altered. If the spheres were all exactly the same size and assumed the theoretical close-packed arrangement, they would occupy 74 per cent of the available space and the sedimentation volume would be 0.60 ml. per gram. This is less than the observed final volume of 0.73 to 0.78 ml. per gram, but agrees with Westman and Hugill (15)who showed that most powders of uniform size and shape pack to a void space of about 36 to 40 per cent. The minimum value obtained for the sedimentation volume was the volume of the sedimented particles in water. No volumes were ever obtained in any liquid which were less than this, and it is assumed to be the volume corresponding to the closest packing attainable by free settling. This minimum value signified that the particles were not flocculated and, in settling, were acting independently of one \MERCURY CUTOFF another.
1
'I,
Discussion of Results On the basis of the experimental facts presented, it is apparent that the sedimentation volumes of glass spheres in organic liquids are small and identical with that in water; and in these systems any increase from this minimum value is due to the presence of water either in the liquid or adsorbed on the particles. The facts which support this conclusion are: (a) Sedimentation volumes of the spheres are at the minimum in water and water-miscible organic liquids. (b) I n liquids in which water is only slightly soluble, the final volumes are small if the liquids are pure and dry, or can be made to approach the minimum value as the dryness of the system is increased. (c) Large sedimentation volumes are obtained in all liquids saturated with water, and a t lower concentrations of water the effects depend on the nature of the liquid.
ELECTRIC FURNACE
FIGURE 3.
V.iCEUM APP.4RATUS FOR DETERMINING SEDIMENThTION VOLUMES
INDUSTRIAL AND ENGINEERING CHEMISTRY
JUNE, 1940
interface, glass-organic liquid, this adsorbed layer or film will play an important part in determining the behavior of the sedimenting particles. The amount of the adsorbed water will depend on the concentration of water present. If it is adsorbed in sufficient quantities to be present as liquid water, the interfacial tension of this film against the bulk of the organic liquid should be directly related to the tendency of the particles toward flocculation.
TABLE VIII. PROPERTIES OF LIQUIDS Dielectric InterCon. mentafacial Dipole etanl tion To]. Tension (91 Moment (14) ( 1 0 ) Sedi-
Liauid
.‘dl,/y.
Water Ethvl alcohol Acetone n-Propyl alcohol n-Butyl alcohol Benzyl alcohol Amyl alcohol Ethyl acetate Aniline Nitrobenzene Benzene CCli a
Dynes/cn.
...
E . s. u . X 10‘8
187
0.73 0 75 0.73
...
1 7 2.9
0.79
4:75
1.7 1.7 1 8 1 6 3.9
0.73 0 75 0.75
0 0 0 0
85a 75 75 79 0 92a
5.0
6.65(7,
5,77
25.66
35.00 45.0
6 0 257
:i
21 4 21 8 17 S 13.0 16.8
0.0
36. 2.7h 2.24
0 0
6.4 7.2
Sol?. of Water at 20° C. (IS) G./lOO y. soln. ,.. m m m
20 27 8.37 (4A) 9.6 3 01 4 83 0 22 0 0573 0 00844
831
The effect of the presence of water has not been thoroughly appreciated by previous investigators. Harkins and his coworkers did not study the effect of water dissolved in the liquids, although they found that intensive drying of the pigments would decrease the sedimentation volumes. Their results are affected to some extent by the fact that the powders they used present more possibilities for reactions with water and the suspending media. The quartz particles used by von BuzBgh should behave similarly to glass. However, his results indicate that his systems were not absolutely dry. Since water is a common impurity which is usually neglected in this type of work, we have devoted our entire attention to its effect on dispersions of glass spheres in organic liquids We have not studied the effect on other solid particles than glass or the effect of inorganic salts, wetting agents, and either miscible or immiscible liquids, other than water, on dispersions of this type. This paper records the experimental observation of the effect of water on the sedimentation of glass spheres in organic liquids. The theoretical aspects and the nature of the adsorbed layer of water on the particles, and the quantitative relationship between interfacial tensions and sedimentation volumes and flocculation will be treated in greater detail in mother paper.
Ultimate dryness not obtained.
Acknowledgment Sedimentation volumes of glass spheres in dry liquids and the tensions of the organic liquid-water interface are given in Table VIII, together with dipole moments, dielectric constants, and the solubility of water in the liquids. The data show that the sedimentation volumes in all of these liquids are nearly the same although there is a wide variation in other properties. Contrary to the findings of other investigators, this indicates that the dipole moments and dielectric constants have a n influence on the sedimentation volumes only in so far as they affect interfacial tensions and solubility. On the basis of the interfacial tension of the organic liquids against water the liquids may be divided into four classes: 1. Pure organic liquids with high interfacial tensions (greater than 30 dynes per cm.) produce large sedimentation volumes unless extreme precautions are taken to remove all traces of adsorbed water from the particles by evacuation and heating. The liquids must also be intensively dried. The amount of flocculation and the sedimentation volume increase with the concentration of water, and the effects are large. Liquids in this class, such as benzene, are relatively inert chemically, and water is practically insoluble in them. 2. I n liquids with slightly lower interfacial tensions, the sedimentation volumes increase with the water content of the solutions, but it is not difficult to obtain the minimum value by drying the liquid alone. Examples are nitrobenzene and ethyl acetate whose interfacial tensions against water are 25.66 and 6.65, respectively. The solubility of water in these liquids is small but considerably more than in benzene. 3. Liquids with low interfacial tensions (less than 6 dynes per cm.) produce small sedimentation volumes unless the liquids are nearly saturated with water. Examples are amyl and benzyl alcohols and aniline. The interfacial tensions of these liquids against water are 5.00, 4.75, and 5.77 dynes per cm., respectively. These compounds have active groups which tend to increase the solubility of water in them. 4. Liquids with zero interfacial tensions are miscible with water and have no tendency to cause flocculation of the suspended particles or increase the sedimentation volume above the minimum value. Under these conditions it is not possible to form a water film about the particles.
Acknowledgment is made to the Research Education Division of Battelle Memorial Institute for the support of this work.
Literature Cited (1) -4kamatsu,H., Bull. Chem. SOC.Japan, 13, 456-62 (1938). (2) Bloomquist, C. R., and Clark, A., IND. EKG.CHEM.,Anal. Ed., 12, 61-2 (1940). (3) BurLgh, A. von, Kolloid-Beiheftftr,32, 114-42 (1930). (4) Davis, H. S., J . Am. Chem. Soc., 38, 1166-78 (1916). (4A) Doolittle, A. K., IKD. ESG.CHEM.,27, 1169-79 (1935). (5) Freundlich, H., and Jones, 4.D., J . Phys. Chem., 40, 1217-36
Freundlich, H., and Roder, H. L., Trans. Faraday SOC.,34, 308-16 (1938). Halberstadt, S., and Prausnitz. P. H., Z . angew. Chem., 43, 970-7 (1930). Harkins, TV. D., and Gans, D. M., J . Phys. Chem., 36, 86-97 (1932). International Critical Tables, Vol. I V , p. 436. New T o r k , McGraw-Hill Book Co., 1928. Ibid., Vol. V I , pp. 83-96 (1929). Ostwald, Wo., and Haller, W., Kolloid-Beihefie. 29, 354-95 (1929). Ryan, L. W., Harkins, W. D., and Gans, D. M . IND.ESQ. CHEM.,24, 1288-98 (1932). Seidell, A., “Solubilities”, 2nd ed., New York, D. V a n Nostrand Co.. 1928. Sidgwick, N. V., Trans. Faraday Soc., 30, 904 (1934). Westman, A. E. R., and Hugill, H. R., J . Am. Ceramic SOC., 13. 767 11930). Willkznson, R. V., and Heckert, W. W., IKD. ENG.CHEM.,23, 667-70 (1931).
Correction-Froth Flotation Concentration In the article by C. C. De Witt in the May, 1940, issue of IXDUSTRIAL AND EKGINEERING CHEMISTRY, an error was made in designating the Denver Equipment Company’s Denver Sub-A (Fahrenwald) and the American Cyanamid Corporation’s (Fagergren) flotation cells. The captions for these pictures should have been reversed (pages 653 and 655). The author’s address is erroneously given as Michigan College of Mining and Metallurgy instead of Michigan College of Mining and Technology.
