Superheating and Foaming Phenomena in Dehydrating Emulsified

SUPERHEATING AND FOAMING PHENOMENA IN DEHYDRATING EMULSIFIED OILS’ GUSTAV EGLOFF AND SOPHIA BERKMAN Research Laboratories, Universal Oil Products Co., Chicago, Illinois

Received July g, 1934

Crude petroleum oil, whether obtained from a level of a few hundred feet in the earth’s crust or from a level of more than nine thousand feet, usually contains water. When oil and water pass through pipes to the earth’s surface, or when pressure is released, an emulsion forms. As a matter of fact, over 200,000,000 barrels (42 gallons each) of emulsified crude oil are dehydrated yearly by means of heat, heat and pressure, chemicals, electrical energy, or combinations thereof. Crude oil emulsions are usually of the water-in-oil type, while a few show the oil dispersed in water. Some manifest a double type emulsion of water-in-oil and oil-in-water, while others are of the water-in-oil type with oil also dispersed in the water drop. The water content of emulsified crude oils may vary from 0 per cent to over 90 per cent as produced. Emulsified crude oils are, in general, of a highly complex character; this study is directed toward their superheating and foaming characteristics. The dehydration of emulsified oil by heat is based primarily upon lowering the viscosity and surface tension and changing the colloidal properties of the emulsifier. It is difficult to generalize on the specific effect of heat in the sense of changing the properties of the emulsifier, because the effect produced depends more upon the individual case to be treated, i.e., the nature of the components involved and the physical conditions of the syatem. A suitable increase in temperature is combined with a change in the state of aggregation, and the steam and oil vapor formed cause breaks in the surrounding protective films. Heat does not effect the separation of water and oil directly, but rather accelerates it. The accelerated precipitation of water does not occur solely on account of the increase in the difference in the specific gravity of the components due to heating. A more rapid precipitation of water on heating may be attributed rather to a decrease in the viscosity of the oil. The temperature to which an emulsion must be heated for complete dehydration depends to a certain extent upon the nature of the crude oil emulsion and may vary widely. When Presented a t the Eighty-fifth Meeting of the American Chemical Society, held in Washington, D. C . , March 30, 1933. 265

266

GUSTAV EGLOFF AND SOPHIA BERKMAN

the temperature is increased, the density of the hydrocarbon oils decreases more rapidly than the density of water. In heating an oil from 15.5565.5"C., the decrease in density amounts to about 7 per cent, whereas in heating water from 15.55-65.5"C., the decrease in density amounts to 1.1 per cent. For this reason it is possible to obtain a more rapid separation of oil and water a t higher temperatures than a t lower temperatures. At a given temperature and with oils of equal specific gravity, the one having the lower viscosity will separate more readily from water. This effect is pronounced when the amount of oil is large as compared with the amount of water. Increasing the temperature of an emulsified oil from 15.5565.5"C. reduces its viscosity a t times as much as 55 per cent. The rate of separation varies with the amount of material charged to the still, the size of the still, the amount and degree of dispersion of the water present in the oil, and the stage of the process. Two phenomena, well known to the industrial chemist, accompany heat dehydration: first, a priming or puking of the oil to be dehydrated, a kind of explosion caused by a superheating effect; second, foaming of the emulsion. Observations reveal that there is a certain relationship between these two phenomena. Some form of heat treatment is generally used for the removal of water from oil emulsions, therefore it is of interest to discuss both these phenomena. If an emulsified oil is heated too rapidly, it usually causes the still t o puke. Sometimes puking of the oil is effected by irregularities occurring in heating. Occasionally, when the same amount of the same oil is charged to three stills of the same size, one pukes more readily than the others. Marcet (14) was the first to note that the temperature a t which water and certain other liquids begin to boil varies with the nature and the state of the surface of the container in which the boiling takes place. These differences were attributed to a molecular change produced by the surface of the container, or by the presence of certain substances. It has been suggested that the part these substances play is to produce a more or a less perfect contact, or a more or a less close adhesion between the molecules of the liquid and the walls of the container. Whether the conversion of the liquid into vapor is made more difficult or, on the contrary, facilitated, is determined by the action of these substances. Evaporation and ebullition are both molecular phenomena. Both, depending upon the action of heat, differ in the degree of vapor tension produced, as well as in the rapidity with which the change of the liquid into a vapor takes place. While in ebullition the change of the phase is sudden and visible, occurring simultaneously throughout the liquid, the change of the phase in evaporation is slow and always progressive, restricted to conversion into molecular vapor situated a t the surface, or very close to it. Any factor increasing the cohesion of the molecules to each other, or their

SUPERHEATING I N DEHYDRATING EMULSIFIED OILS

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adhesion to the walls of the container in which they are enclosed, would have a tendency to slow down the evaporation of this liquid or delay its ebullition. Donny (4),Dufour (5), and Faraday (6) found that water freed from air does not boil until it reaches a temperature of 132°C. and then it explodes. Water raised to a temperature of 132°C. under ordinary atmospheric pressure remains as water, but the introduction of the smallest amount of air or steam induces it to vaporize immediately and, a t the same time, its temperature decreases. Donny assumed that the superheating phenomenon was due to a rupture either in the cohesion of the heated liquid, or in its adhesion to the container. Under ordinary conditions, liquids begin to boil approximately at a temperature required by their vapors so as to establish equilibrium with atmospheric pressure. By the effect of ebullition, liquids lose the greater part of the air held in solution, the boiling of the liquid being influenced principally by cohesion and adhesion. The liquid, free from air and heated beyond its boiling point, finally releases vapor explosively when a lowering of the temperature brings back a momentary quietness to the liquid. Cohesion is the force preventing, or a t least delaying considerably, ebullition of liquids free froni air. The phenomenon of priming or puking once started continues to reproduce the effect with an increasing violence. If the principle that the liquid has to be freed from air in order to produce the above phenomenon holds true then, by passing a gas through a liquid, the disturbing phenomenon may be avoided. Donny’s experiments revealed that this holds true only for certain cases. De la Rive (3) and Dufour (5) studied the change of phases under the influence of temperature. They pointed out that the presence of a foreign substance in a liquid may hasten the evaporation, assuming that the change in phase does not necessarily occur when by heating the liquid a tension equal to the outside pressure is produced, but it may occur partially, owing to certain molecular conditions of the contact to which the liquid is subjected. The molecular influences of contacts tend to promote vaporization a t a minimum temperature. Owing to this fact, noticeable differences in boiling point are observed when water, alcohol, or sulfuric acid is heated in a glass or in a porcelain container (experiments by Donny (4),Marcet (14), and Magnus (12)), or when they are heated away from contact with solid particles. I n some cases it appears that the contact of solid particles is B determining cause of the change of phase for fluids. If a globule of liquid comes in contact with a solid particle entrained by currents induced by heat, or with the walls of the container, a sudden production of a vapor bubble takes place. If water is mixed with sand (3) with a liquid layer of a few millimeters thickness, the water evaporates more rapidly in air than the same quantity of water alone. Thus the temperature of a water-sand

268


mixture evaporating in air is lower than that of water exposed alone under the same conditions. Water containing sea salt also evaporates less rapidly, producing a smaller degree of cooling by its evaporation than water under the same conditions. Kenrick (10) and his coworkers studied the superheating phenomenon of liquids. A study was made of the extent to which liquids may be superheated and the physical conditions under which superheating is possible, i.e., where temperatures are equal to or higher than those where the elastic force of the liquid produces equilibrium to the external pressure. The question regarding the location of the ebullating and superheating influences also appeared of interest to these investigators. They assumed that ebullition takes place locally, either at a few fixed points on the walls of the TABLE 1 Association coeficient of liquids as determined b y G i l b e r t LIQUID

Ethyl ether ..................... Ethyl alcohol.. ...................... Methyl alcohol. .....................

.......... Acetone .............................

Sulfur dioxide. ...................... Benzene . . . . . . . Chlorobenzene. ...................... Bromobenzene ....................... Aniline. . . . . . . . . . . . . .... m-Xylene ............................

HIQHEST TEMPERATURI

PRESSUR1

BOILINO POINT

degrees C.

mm.

degrees C.

143 201 180 173 174 168 270

11,500 22,700 20,100 11,000 14,400 11,700 41,200 6,300 11,200 8,300 G ,100

50

203 250 261 262 235

35 78

63 61 56 46 100 - 10

79

ASSOCIATION COEFFIClnNT

1.0 2.7 3.4 1.0 1.3 1.0 2.3-3.8 1.0 1.0

132 156 183 137

vessel, or from particles suspended in the liquid from which actually streams of bubbles rise. If this be true, then the superheating effect should depend on the ability of the liquid to wet the material which serves as a nucleus. Kenrick found a gradation in the effectiveness of the nuclei present. Some of them caused ebullition when the liquid was slightly superheated; others were effective only when it was heated to a higher temperature. Experimentally, it was not clear whether there was a real temperature limit or merely a rapid shortening of the time interval with increase in temperature. He also found that the smaller the vessel in which the liquid is heated, the higher the temperature to which it could be heated without boiling, Wismer (19) calculated the diameter of a spherical particle act-

.

SUPERHEATING IN DEHYDRATING EMUI&IFIED OILS

269

ing as a nucleus enclosed by bubbles and found that it was equal to 5 X lo-' cm. Calculation of the pressure in the bubbles gave a value of about 12.5 atmospheres, corresponding to a temperature of about 130°C. (extrapolated). Gilbert (7) calculated the amount of vapor in a bubble whose pressure, caused by surface tension, balances the outside vapor pressure. Quantities about one hundred times greater than those corresponding to the ordinarily accepted molecular dimensions were determined. This led Gilbert to the conclusion that liquids which can be heated to temperatures corresponding to abnormally high vapor pressures are those which are abnormal in possessing high association coefficients as shown in table 1. Wismer (18) determined the pressure-volume relations for ether a t 121", 128", and 134°C. and a t corresponding pressures above 30 atmospheres to as low as 1 atmosphere. He made similar measurements with ethyl chloride a t 99", l l O o , and 117°C. The P-V curve in both cases appeared to be almost a straight line, and showed no sign of more rapid curving as the limit of superheating was reached, although in both cases the temperatures reached at atmospheric pressure were above the maximum calculated from van der Waals equation. The most characteristic points in the superheating effect are the extent to which superheating of a given liquid is carried out and the time during which a liquid is kept under these conditions. It was observed that these characteristics vary from one experiment to another. Kenrick, Gilbert, and Wismer (9) attempted to work out these questions concerning superheating phenomenon. Previous work (1, 20) indicated that the superheating of liquids is closely allied to the "stretching" phenomena of liquids (15), as well as to the supersaturation of gases (19). Supersaturation is favored by long heating of a solution at high temperature. Liquids saturated with gases a t concentrations corresponding to a pressure over 100 atmospheres showed that when the pressure was reduced to 1 atmosphere, no bubbles were formed in the liquid. I n the case of superheating of liquids, Kenrick, Wismer, and Wyatt observed that with a rise in temperature there is a very rapid shortening of the time interval between the lowering of the pressure and the formation of bubbles, in spite of the fact that the adsorption coefficient of the gas decreased but little with rise in temperature. There is definite evidence in favor of the old theories on the superheating phenomenon, namely, that liquids must be free from gases and air in order to undergo superheating effects. Krebs (11) removed air from water by mixing it with alcohol (about three times the volume of water) and boiling down the mixture to a small volume (the boiling point rose steadily to 107°C.). When a very large flask was used and the mixture evaporated to a small volume, the boiling point could be increased still more. I n the boiling of this water-alcohol mixture, Krebs observed for the first time the coexistence of superheating and foaming.

270


There is a certain analogy between the superheating phenomenon in liquids and in emulsion systems. But in the latter, the superheating effect finds its explanation rather in the behavior of the interfacial phase. As early as 1836, Magnus (13) showed that water with oil poured over it presents a considerably delayed ebullition. If oil is poured upon water, the explosive boiling is much more violent. Rideal (16) proved that evaporation of water from a surface is considerably diminished in the presence of fatty acids, such as stearic and oleic, as compared with evaporation from a free surface (8). An increase in the concentration, or in the pressure, upon the surface may also delay evaporation. It is to be expected that surface layers in a condensed or a vapor state primarily influence evaporation. When an oil-water emulsion is heated, the continuous phase, which is covered with a thin layer of oil, must be heated to a higher temperature, to start boiling, than that required to start the boiling of pure water. A sudden decrease from a higher boiling temperature to a lower may be attributed to a change in the Brownian movement during the heating, causing a cessation in the continuity in the interface oil skin and a decrease in temperature. Taylor (17) in his article “The Structure and Decomposition of Liquid Skins” states that monomolecular layers actually have thick spots which interfere with their stability. It is possible that the problem of whether skins in the interface play a part in the explanation of the superheating phenomenon in emulsion systems may be solved experimentally, using dyestuffs. Frumkin, in a work on spreading dye substances on a water surface, proved that a competition of two substances over the same water surface can be demonstrated. When a drop of oleic acid is placed on a water-crystal violet (dye) surface, then the oleic acid molecules displace the dyestuff molecules and the dyed layer sinks to the bottom in streams. On a water surface previously covered with an oleic acid film, the crystal violet particles of dye remain colorless upon the surface. Tetraiodofluorescein may be used similarly. Perhaps, by means of such a dyestuff, it will be possible to prove whether superheated water in an oil-water emulsion is actually covered with a thin layer of oil, causing a decrease in evaporation, depressing ebullition and, consequenkly, producing the superheating effect during dehydration of crude oil emulsions. Foaming is a phenomenon intimately connected with heat dehydration of emulsified oils. Emulsions, in their original form, often cannot be subjected t o distillation without high danger of foaming over. The foaming is, of course, undesirable, not only because distillation must be repeated, but also because of the ever-present danger of fire. A belief is entertained that incipient foam formation with a rapid breaking down of the foam may play a large part in the mechanism of dehydration itself. Pressure and high temperature are two factors which favor the dehydration process, reducing

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271

a t the same time the foaming tendency of the emulsion system. Pressure weakens the foam film structure; a t higher temperatures the ability of oil to make and to maintain individual foam laminae is decreased. I n petroleum emulsions the emulsifying agent is usually asphalt, “soaps,” or mineral matter, and the decreased foaming with increase in temperature is due less to change in composition a t the temperature a t which foaming ceases than to a decreased protective action. A number of experiments were carried out in connection with foam formation in heat dehydration of emulsified crude oils. The first question arising in connection with the problem concerns itself with the conditions under which foam originates in crude oil emulsions. 1. It was found that for the same temperature more water may be separated from an emulsion where a vapor space is present, than where no vapor space exists. When one-quarter, one-half, or three-quarters of the still capacity was charged with a crude oil emulsion having 36 per cent of water and heated to 121.1”C. under a pressure of 2.74 kg. per square centimeter, 10 to 12 per cent of water was separated. When a full charge was maintained a t the same temperature, 121.loC., although using a pressure of 3.31 kg. per square centimeter only 6 per cent of water separated out. The lack of vapor space prevents substantial foam formation which, in all probability, accounts for the difference in the dehydration effect. 2. A series of tests was made with sixteen samples of California emulsified oils to determine their foaming properties. The emulsified oils to be investigated were charged in beakers, immersed in a glycerol heating bath, and the foaming properties and height of the foam noted. The California emulsified oils which were experimented with had a water content ranging from 6 per cent to 69 per cent. The temperature of the glycerol bath in these comparative tests was maintained constant at 177°C. It was found that under the temperature conditions prevailing the foam column in the emulsified crude oil varied from 13 in. to over 5 in. in height. It is interesting to note that a mixture of California oils No. N6 and N2 taken in equal portions showed a foam column height which was higher than when the oils were subjected singly to the same heating. California oil No. N6 with 6 per cent water: foam height, 3.8 em. California oil No. N2 with 30 per cent water: foam height, 10.5 em. A mixture of the two oils in equal proportions: foam height, 11.8 em. This brings out, as far as these tests are concerned, that the properties of emulsified crude oils as to foaming are not additive when mixed. One would expect that the foam column of California oil No. N2 would be reduced, owhg to the addition of an oil having a low water content. However, this is not the case. As a matter of fact, the diluted oil No. N6 did not decrease the foam column, but actually increased it.

272


3. Distilling of crude oils of different origin revealed that foam formation in emulsified oils depends greatly upon the nature of the crude oil. The crude oils compared were derived from Casmalia, Santa Maria, Lompoc, and Efson oil wells. Casmalia oil is very persistent in foaming; Santa Maria oil foams slightly; Lompoc oil foams strongly; Efson oil foams, showing explosive characteristics. Some emulsified oils distill quickly and then begin to foam after distillation has proceeded for a while, whereas other oils foam violently from the beginning of heat application. Lompoc emulsified oil from Efson well No. N10 produced more foam a t 149°C. than any Santa Maria crude oil tested, but Casmalia crude oil was the most persistent foam producer of all those experimented with. It was found further that the Lompoc oil acted in an explosive manner when heated. To overcome the violent bumping of this oil, gasoline was added to it and the foaming test conducted. The oil evaporated in a much less violent manner, but spattered and spat during the heating, and the foam was not persistent. This indicates that the gasoline added to the Lompoc emulsified oil has a marked influence upon its foaming and evaporating properties. Some emulsified oils, upon application of heat, form relatively small foam bubbles, while others produce large bubbles., 4. The effect of temperature on the foaming properties of the emulsified oil was studied as a function of the depth of the liquid placed in the tubes. The oil investigated was Santa Maria crude oil containing 29 per cent of water. The procedure was to charge glass test tubes 2.24 cm. in diameter and 20.3 em. long filled with 1, 2, and 3 cc. of Santa Maria emulsified oil which were immersed to 17.8 cm. of their length in a heated glycerol bath. After the glycerol bath reached the desired temperature, the tube containing the emulsified oil was placed therein. At the beginning of the test, the emulsified oil distilled quietly, with little foaming. As vapors passed from the top of the tube, a time was reached when the foam which started in a fine dispersion became coarse and persistent. The foam rising in the tube became at times somewhat irregular, seeming to give a breathing action, but finally attained a maximum and then gradually subsided. The maximum height which the foam column reached was recorded and all comparisons made in a similar manner. It was found that the foam column of the Santa Maria emulsified oil increased as a function of the depth of the oil in the tube, and also increased as a function of the temperature employed, to a maximum which was attained a t a glycerol bath temperature of 140°C., the foam column decreasing as the temperature of the bath reached 176°C. Table 2 gives the order of the foam formation, as a function of the temperature variation, and depth of liquid employed during this set of experiments.

273

SUPERHEATING IN DEHYDRATING EMULSIFIED OILS

j

5. Finally, from a series of tests in which California emulsified crude oils were dehydrated, it was ascertained (a fact already indicated by Krebs (ll),that foaming in heat dehydration was combined with the superheating effect discussed previously, as well as with self-cooling. Usually, during the heating of California emulsified oils, the temperature rose quite rapidly to a little above the boiling point of water, where it remained relatively TABLE 2 Order of foam formation VOLUYB OF EYULSIF'IBD OIL U S E D TlMPERATURlOFBATE

I

100:

a CC.

I

3 ec.

degree8 C.

125 140 180 160 176

16 32 34 26 23

19 52 49 42 33

32

80 70 50 44

TABLE 3 Foam i n heat dehydration combined with superheating efect and self-cooling PHASES I N HEATING PROCESS

TEMPERATUREINDBGREEBC.

CHARACTERISTICS OF FOAMING

Oil sample No. 1

I Phase I1 Phase I11 Phase

I Phase I1 Phase I11 Phase

Up to 111.1 Drop in temperature to 102.2 constant for a time Rise in temperature from 102.7 t o 104.4

Little foaming Foam column rising

Up t o 107.2 From 107.2 to 102.2 From 101.6 to 111.1 At 150.0

Slight foaming Foaming increases Foaming rapidly recedes Foaming almost zero

Foam column starting t o collapse

constant for a time until a portion of the water was distilled from the oil, the temperature rising until a maximum was reached where the oil was dehydrated with a few fine drops of water still dispersed in the tar residue. With several of the emulsified crude oils, a marked departure from the behavior just described was noted. Santa Maria crude oil from Rice Ranch well No. N2 showed a distinct superheating effect with rise in temperature followed by more or less foam-

274


ing, a drop in the temperature of the oil taking place despite the fact that the oil was still being heated. I n other words, water was apparently held in the oil above its boiling point, and by this superheating suddenly formed steam, with cooling taking place in the liquid. The mechanism would, therefore, be either that the oil system during this period absorbed heat from the oil faster than from an external source to an extent of producing a cooling effect (manifested by an actual drop in the temperature of the oil), or, under critical temperature conditions, the protective films were ruptured, or else chemical changes occurred in the emulsifying agent (a dissociation of the hydrates of the hydrocarbons present in the emulsified crude oil system), which took heat from the system, thereby cooling it. I n table 3 are illustrated (on two samples) the three phases in heat conditions of a Rice Ranch Santa Maria crude oil emulsion accompanied by foaming. SUMMARY

Two phenomena accompany heat dehydration of emulsified oils : priming or puking, and foaming, resulting from superheating water. Superheating of various liquids may be compared with superheating of emulsified oils. The conversion of a liquid into its vapor state is influenced by the ,character of the surface of the container in which the boiling occurs, or by the presence of solid particles in the liquid. Cohesion of molecules of the liquid or their adhesion to the walls of the container or suspended solids slows down evaporation and delays ebullition. Liquids freed from air are apparently a critical condition for the delay in ebullition. The extent of superheating is determined by the temperature necessary for sustaining equilibrium of the liquid against external pressure. Ebullition is restricted to certain localities in the liquid. A gradation in the effectiveness of the material serving as a nucleus for the superheating phenomenon is observed. The extent to which superheating of a liquid is carried out, and the time during which it is held under a superheated condition are the characteristics and the variables in the process. An analogy between superheating and foaming effects in liquids and emulsions may be postulated, considering the significance of the interfacial phase in the case of emulsions. A thin layer of oil spread upon superheated water in an oil-water emulsion is responsible for the decrease in the evaporation of the system, depressing ebullition. The mechanism of dehydration includes, in addition to the prevention of the superheating influences, the break-down of foam formed during the process. Pressure and high temperature favoring dehydration likewise reduce the tendency of the emulsion system to foam. At the same temperature, more water may be separated from an emulsion where a vapor space is present than where no vapor space exists. The lack of vapor

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space substantially prevents foam formation, thus accounting for changes in the dehydration effect. The properties of emulsified crude oils with respect to foaming are not additive. The intensity and persistence in foaming of emulsified oils which are to be dehydrated is decided by the nature of the oil. Foaming and evaporation of water from the emulsified oil are markedly influenced by certain substances, for example, gasoline. The foaming of emulsified oil increases as a function of the depth of the oil in the container, reaching its maximum a t a definite temperature. Superheating and foaming observed in the dehydration of emulsified oils produce evidence for the existence of a self-cooling effect. The latter may be interpreted as a result of superheating when the heat from the oil is adsorbed faster than from an external source. It may also be due to a rupture of protective films or else to chemical changes occurring in the system, requiring heat to be taken from the system itself and thereby cooling it. REFERENCES

(1) BERTHELOT: Ann. chim. 30, 232 (1880). M. E.: Compt. rend. 62, N19 (1861). (2) CHEVREUL, (3) DE LARIVE:Ann. chim. 23,209-17 (1823). (4) DONNY:Ann. chim. 16, 167-90 (1846). Pogg. Ann. 67, 562-83 (1846). (5) DUFOUR:Compt. rend. acad. Sci. 11, 63, 846-9, 986-9 (1861);Lieb. Ann. 121, 365-9 (1862); Paris Cosmos 23,5-7 (1863). (6) FARADAY, M.: Royal Institution, June 7, 1850. (7) GILBERT,C. S.: Trans. Roy. SOC.Can. 16,353 (1921). (8) HEDESTRAND: J. Phys. Chem. 28, 1244 (1924). GILBERT,AND WISMER:J. Phys. Chem. 28, 1297 (1924). (9) KENRICK, (10) KENRICK,F.B.: Trans. Roy. Soc. Can., 1921, 1922,1924. (11) KREBS,G.: Pogg. Ann. 136, 144 (1869); Ann. Chem. 26, 413 (1889). M.G.: Ann. chim. phys. [3]6,353 (1842). (12) MAQNUS, (13) MAGNUS, M.G.: Pogg. Ann. 38,481 (1836). (14) MARCET,F.: Compt. rend. 14, 1586-9 (1842): Lieb. Ann. 44, 158-61 (1842); Pogg. Ann. 66,170-4 (1842);refer also to Archives of Physical and Natural Sciences, April, 1853. (15) MEYER,J.: Nernst Festschrift, p. 278 (1902). (16) RIDEAL,E.K.:J. Phys. Chem. 29, 1585 (1925). W.: Ann. phys. [lo]1, 134-70 (1924). (17) TAYLOR, (18) WISMER,R. L.:Trans. Roy. Soc. Can. 49, Section I11 (1921). (19) WISMER,R. L.: Trans. Roy. SOC.Can. 16, 271 (1922). Phil. Trans. 183,355 (1892). (20) WORTHINQTON:

Superheating and Foaming Phenomena in Dehydrating Emulsified

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