September, 1929
INDUSTRIAL AXD ENGIh’EERIXG CHEXISTRY
.Vole-Edser (1) explains t h e behavior of bubbles under t h e surface of a solution in much t h e same way a s given above. His phraseology is as follows:
So long a s t h e bubbles remain stationary t h e osmotic pressure due t o t h e local concentration in t h e space between t h e bubbles will be balanced b y the molecular forces t h a t produce t h e concentration; b u t when t h e bubbles begin t o approach each other, a change occurs in t h e molecular forces producing t h e local concentration, with t h e result t h a t t h e osmotic pressure becomes unbalanced, and t h e unbalanced force will tend t o stop the motion of t h e bubbles. T h e writer confesses t h a t t h e full significance of Edser’s words escaped him till after he had formulated his own theory. T h e two appear essentially t h e same, however, b u t with this difference: Edser’s explanation was applied t o a specific situation only, whereas t h e writer’s ppint of view is general i n making the theory apply t o all cases of t h e approach 0’ liquid surfaces t o each other.
It can iiow be seen that the general theory as ontlined above harmonizes the seemingly coiiflicting experimental facts listed earlier in the paper. It shows that films of pure liquids do not form because there is no surface layer of different composition t o resist a force tending to produce homogeneity. It also shorn that it, is immaterial whether the surface layer is more or less concentrated than the mass of the liquid. I n either case there is a layer on which work must be done to produce uniformity of concentration and it will therefore resist any force tending t o bring this about. This also explains why the effect is the same whether the surface tension is raised or lowered by the dissolved matter. There remains, finally, the effect of antifoams. There is little published experimental work on this point, though something has been done in the author’s laboratory. It offers a field of research in which, it is hoped, the new theory will be a useful guide. There is much experimental evidence in favor of the theory. Edser has already described the situation with respect t o bubbles under the surface, and numerous experiments of this sort have been made in the author’s laboratory. These will be described in detail in a subsequent paper. The most striking experiment, however, that shows the effect of dissolved matter is one recently devised by the writer, the technic of which has been perfected by J. N. Miller in the Ohio laboratory. It consists simply in causing two bubbles t o issue from orifices placed near each other under the surface of
817
a liquid so that the bubbles will be forced to touch. I n a solution they will flatten against each other or roll over each other but will not coalesce. I n a pure liquid, however, they merge a t once and rise to the surface as a single bubble. This simple experiment, it is seen, suggests a new method for studying liquid films, because it eliminates entirely the effect of the stability of the film as it would exist in a mass of foam exposed to the air. Stability of Films
Beyond a fev general observations, no discussion of the stability of films will be attempted here. It is the author’s view that film formation and film stability are separate questions. So far as the theory advanced above is concerned, it is sufficient to say that a film is formed whenever two liquid surfaces, in approaching each other, pause long enough for a n observation to be made. This might be as little as a thousandth of a second. It is a t least clear that there can be no dividing line between stable and instable films, because it can be shown experimentally that some bubbles last for only a fraction of a second and others for days or weeks, with all stages between. I n an industrial situation practical conditions alone are decisive. I n ore flotation, for example, the bubbles should last long enough to carry over the valuable minerals, and in a steam boiler they should not last long enough to reach the steam lines. The stabilizing and destabilizing of foams is thus seen to be a problem of major importance, in the solution of which the general theory of film formation as proposed above may be of service. Literature Cited ( 1 ) Edser, 4th Report on Colloid Chemistry, British Assocn. for Advancement of Science, 1922, p. 318. (2) Foulk, IVD. ERG CHBM., 16, 1121 (1924). (3) Foulk, M e c h E n g , 48, 1364 (1926), J . .Am. W’aler W o v k s Assocn., 17, 160 (1927). (4) Freundhch, “Colloid and Capillary Chemistry,” p. 793, Methuen and C o , L t d , London, 1926. ( 5 ) Gibbs, Scientific Papers (6) Ostwald and Steiner, Kolloid-Z., 36, 342 (1926).
Laboratory Experiments with a Foaming Boiler Water‘ A. S. Behrman ISTERN.4TlOKAL
FILTER CO.,
Laboratory tests indicated great improvement as regards foaming when organic coloring matter mas removed from a boiler water, either by coagulation and filtration or by oxidation. On the strength of these experiments provision has been made for the treatment of the water with aluminum sulfate and sulfuric acid for the removal of the suspended and organic matter.
cHIC.&CO,
ILL.
carbonate recommended for the inhibition of caustic embrittlement. Typical analyses of the raw water and of the boiler blowdown- are shown below: R a w WATER
P. 9 . m.
Alkalinity: Phenolphthalein l l e t h y l orange Total dissolved solids Suspended matter Sulfates (as SanSOt) Color, intense dark brown
T
HE sample of water used in these experiments was taken from a boiler which foamed so badly that the highest concentration of dissolved solids which could be carried under normal operating conditions \vas about 150 grains per gallon (2550 p. p. m.). The boiler3 are of the Sterling type, provided with excellent circulation and adequate steam space. The boiler feed mater was taken from a highly colored surface supply, filtered very roughly, and then softened in a zeolite softener. The zeolite-softened water mas then treated with sulfuric acid in order t o maintain the ratio of sulfate t o 1 Received April 2, 1929.
BOILERB L O W D O W N P . p. m. Hardness (as CaCOJ) 9
Total solids Color, i 0
li0 420 2600 200
1870
208.3
Examination of these analyses reveals only two items which a t first glance might be associated with a tendency towards foaming-namely, alkalinity and color-producing organic matter. When the sample of water taken from the boiler was received in the laboratory, it was observed that merely shaking the bottle produced a very copious and very lasting foam.
INDUSTRIAL A X D EiVGIiVEERISG CHEMISTRY
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This observation led to the following series of experiments, which had for its object the determination of the influence of the alkalinity and the color-producing organic matter on the foaming tendency of the liquid as observed by a simple shaking test. Although it was understood that there was not necessarily a proportional relation between the tendency of a given water to foam when shaken in a bottle and when used in a high-pressure boiler, it was believed that the experiments might isolate the substances or conditions contributing to that film stabilization which Foulk has shown to be so intimately related to foaming. I n the first two experiments described the effect of the alkalinity was studied. I n one case about 90 per cent of the total alkalinity (to methyl orange) of the sample was neutralized with 0.5 N sulfuric acid. I n another case suficient acid was employed to make the liquid definitely acid. I n the remaining experiments the effect of suspended matter was investigated. Here the attempt was made to remove as much as possible of the suspended matter, including the colloidal organic matter which was thought might be primarily responsible for the foaming tendency. It was appreciated that this removal by ordinary methods of coagulation and filtration would probably be incomplete, owing to possible decomposition and increased peptization of the organic matter originally present in the water by reason of the high concentration of alkali and elevated boiler temperatures. Aluminum sulfate and ferric chloride were used as coagulants. The former gave poor results, as was expected, due in part a t least to the abnormal alkalinity of the liquid. Ferric chloride gave much better results. I n view of the incomplete removal by coagulation of organic matter, as evidenced by the residual color, the effect of several oxidizing agents mas tried, of which aqua regia alone gave promising results. I n order to avoid confusing the effect of oxidation and of acidification, one sample that had been given the treatment with aqua regia was subsequently neutralized with sufficient sodium hydroxide to bring the pH up to approximately the original value in the boiler water. The several treatments employed are shown in the following table, and are numbered for the purpose of identification in the succeeding tabulation: TREATMENT
N'O.
1 2 3 4 5 6 7 8
Control-no treatment; p H 11 6 Xeutralization of 90 per cent of alkalinity; p H 5 2 Excess of acid; p H approximately 2 6 Aluminum sulfate, 10 grains per gallon (170 p p m ) ; P H 11 6 Ferric chloride, 10 grains per gallon (170 p p m ) , p H 11 6 Ferric chloride, 20 grains per gallon (340 p p m ) , p H 11 2 Aqua regia Neutralization of (7) with NaOH t o p H 11.6
T'ol. 21, s o . 9
The treated samples, all of approximately like volume, were placed in 8-ounce (226.8-cc.) glass-stoppered bottles, shaken simultaneously in a shaking machine for 5 minutes, and then allowed to stand in a vertical position until the foam broke. Two end points were noted, with the results noted in the tabulation below-the time required for the first breaking of the foam to the point where the surface of the liquid could be seen a t any point, and the time required for the disappearance of all bubbles. h'o 1 2 3 4 6 7 8
TIME FOR FIRST BREAKING TIMEFOR D I S A P P E ~ R A SOCFE OF FOAM BUBBLES Hours Mtn. Sec. Hours Mzn. Sec. 23 40 Not detd. 22 40 Not detd. 0 39 .. 1 1 45 Not detd' ' n 4 X n 40 _. .. 3 15 0 25 .. 0 0 4 30 0 1 10 0 4 30 0 1 10
.. ..
The next step logically was to observe the behavior of the treated samples on boiling. This was done in round-bottom flasks fitted with reflux condensers. The results agreed in general ivith those obtained in the shaking tests, although it was obviously not possible to obtain a quantitative comparison in this case. The experiments described indicate the important influence of colloidal organic matter on the tendency of the sample to foam under the conditions employed. Interesting also is the reduced tendency toward foaming under acid conditions, although the effect is not so marked as that produced by the removal of organic and suspended matter. The tests in themselves gave no absolute assurance that if the suspended and organic matter were removed from the boiler feed water the foaming tendency of the water would be greatly reduced. The qualitative indications, however, pointed so strongly in this direction that provision has been made for a material reduction in the amount of organic and suspended matter in the boiler feed mater. A filter plant has just been completed in which approximately 250,000 gallons of boiler feed water will be treated daily with aluminum sulfate and sulfuric acid to effect the desired reduction in suspended matter. The color is reduced to 5 or less by the treatment. At this writing quantitative results of the treatment, as measured in increased permissible boiler concentrations, are not available. Qualitative observations, however, indicate a very decided improvement in this respect, and it seems reasonable t o expect even more markedly beneficial results when optimum operating conditions have been established.
Distribution of Sulfur in Oil Shale-111' E. P. Harding UNIVERSITY OF hfINHESOTA, MINNEAPOLIS, M I X X .
HE methods used, with one exception, were those described
in the first paper in the series ( 2 ) . It was found that a whiter precipitate of barium sulfate could be obtained if, after adding bromine water and acidifying the filtrate from leaching Eschka's ignition, the filtrate was concentrated nearly to dryness, made just alkaline and boiled, and the precipitate filtered off before precipitating the barium sulfate. SULFUR
SAOPAULO Per cent
the Sao Paulo District, Brazil, and the other from the Musselband Seam of Avonhead, Scotland. The preceding results were obtained. The resinic sulfur is within the limits of experimental error and may therefore be considered as not present in either * shale. The total sulfur in these shales and in those of the preceding papers is distributed as follows:
~IUSSELBAXD
Total
0,5765
0 8819
Sulfide and sulfate Sulfate Sulfide
0.3667 0.0926 0.2641
0.6800 0.1007 0.5793
Sao Paulo Musselband Seam Elk0 Nev. Greeh River, U t a h
Organic Resinic Humic
0.2198 0,0007 0.2191
0.2019 0,0069 0.1950
Mount Logan, Colo.
Two shales were investigated and the results compared with those obtained in the first two papers (1,2 ) . One shale was from 1 Received
July 23, 1929.
PERCENTOF TOTAL Sulfate Organic Per cent Per cent 45.Sl 16.06 38.13 65 69 11.42 22.89 72.62 8.21 19.17 37 24 13 26 49.50 46.43 6.30 47.27
TOTAL SULFUR Sulfide Per cent Per cent
Per cent
0.5765 0.8819 4,946 1.101 1.373
Literature Cited (1) Harding a n d Dumke, IND.ENG.CHEM.,20, 164 (1928). (2) Harding and Thordarson, I b i d . , 18, 731 (1926).
