HYDROUS LANTHANUM HYDROXIDE AS EMULSIFYING AGENT
259
SUMMARY
The O"C., 25"C., and 45°C. isotherms for the system silver sulfatealuminum sulfate-water have been determined. The stable solid phases at these temperatures are AgZSOd and Alz(SO&.18H20. There is no evidence of the formation of silver alum as a solid phase at the temperatures used in this study. REFERENCES (1) CAVENAND MITCHELL: 3. Chem. Soo. l!Z7,2550 (1925). (2) CHUECEAND NORTHCOTE: Chem. News 9, 155 (1864).
(3) KEEN: Chem. News S1,209 (1875).
HYDROUS LANTHANUM HYDROXIDE AS AN EMULSIFYING AGENT THERALD MOELLER' Laboratory of General Chemistry, University of Wisconsin, Madison, Wisconsin Received July 84, 1958 INTRODUCTION
Very little information exists relative to agitating hydrous oxide and hydroxide sols with immiscible liquids, although it has been recognized that certain oxides and hydroxides can stabilize emulsions. Reinders (6) shook several sols, among them ferric oxide, with a number of organic liquids and found the suspended matter to concentrate a t the interface in nearly all cases. Briggs (1) found that a hydrous ferric oxide sol when shaken with either benzene or kerosene gave rise to oil-in-water emulsions providing a small amount of a weakly flocculating electrolyte were present. Klein (2) was unable to precipitate such sols as ferric and aluminum oxides with various organic compounds. In a preliminary experiment in which portions of a hydrous lanthanum hydroxide sol were shaken with equal volumes of different immiacible organic liquids, it was found that white foam-like emulsions floated to the top with benzene, toluene, and xylene. With ether, isoamyl alcohol, carbon tetrachloride, and chloroform, however, emulsions were not produced. 1 Present address: Noyes Chemical Laboratory, University of Illinois, Urbana, Illinois.
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THERALD MOELLER EXPERIMENTAL
For the experiments which follow a sol was prepared which contained 1.492 g. of lanthanum oxide and 0.031 g. of chloride per liter, the purity ratio being 15.7 (3, 4). Carbon dioxide-free water was used throughout, and the organic compounds were of analytical reagent quality.
A . Egkct of sol concentration To each of a series of glass-stoppered bottles containing the amounts of the sol indicated in table 1 was added 15 ml. of toluene. Each bottle was shaken vigorously for 2 min. and observed at once. TABLE 1 Effect of sol concentration using toluene
0 1 2 3
4 5 6
7 8 9 10 11 12 13 14 15
ml.
ml.
0 1 2 3 4 5 6
15 14 13 12 11 10 9 8
7 8 9 10 11 12 13 14 15
Immediate separation to two layers ,
Concentration of La(OH)s at interface
7 6 5 4 3 2 1 0
White foamy emulsion on top
In the bottle containing no sol, no emulsion resulted. Bottles 1, 2, 3, and 4 showed a definite white layer of lanthanum hydroxide a t the watertoluene interface. Beginning with bottle 5, an emulsion formed in each instance, the size of the droplets decreasing with increasing sol concentration. It would thus appear that insufficient lanthanum hydroxide to promote emulsion stability was present until bottle 5 was reached. In the formation of the emulsions, considerable lanthanum hydroxide was removed from the water layer. Similar results were obtained with benzene. The emulsions produced with either liquid were extremely stable and showed no tendency to break.
HYDROUS LANTHANUM HYDROXIDE AB EMULSIFYING AGENT
261
B. Effect of colloiclal gold Into a series of test tubes were measured the amounts of hydrous lanthanum hydroxide sol and gold sol (containing 0.05 g. of gold per liter, undialyzed) indicated in table 2. Five milliliters of toluene was added to each, followed by shaking for 30 sec. Stable emulsions fcrmed until 1.8 ml. of the gold sol had been added, this quantity of gold sol being that required to produce immediate flocculation when added to the lanthanum hydroxide sol. From this point on, although emulsions did not form, there was a concentration of reddish floc a t the water-toluene interface in all cases. TABLE 2 Efect of colloidal gold using toluene La(0H)z SOL
TUBl
~
- __
GOLDEOL
OBBEBVATIONB (AT ONCE)
ml.
1 2 3 4 5 6
j
0
4.8 4.6 4.4 4.2 4.0
, '
0.4 0.6 0.8 1.0
3.4 3.2
1
1.4 1.6
\
Stable emulsion
7 8
9 10 11 12 13 14 15 16
, 2.6 2.4 2.2 2.0
1
2.0 2.2 2.4 2.6 3.0
No emulsion
i
The gold was carried into the emulsion, apparently because of adsorption on the lanthanum hydroxide, for the gold sol alone was incapable of stabilizing an emulsion. As the amount of gold increased, the emulsions became increasingly reddish in color and appeared jewel-like by reflected light. Emulsions containing moderate amounts of gold were stable for indefinite periods.
C. Effect of jlocculuting electrolyfes In order to determine the effects of the presence of various ions, 5-ml. portions of the hydrous lanthanum hydroxide sol were flocculated with excesses of a number of electrolytes. When the flocs had definitely settled, 5 ml. of toluene was added to each, followed by vigorous shaking. An
262
THERALD MOELLER
emulsion, accompanied by the removal of the coagulum from the aqueous layer, resulted in the presence of potassium ferrocyanide, potassium ferricyanide, potassium arsenate, primary, secondary, and tertiary potassium phosphates, potassium dichromate, potassium chromate, potassium sulfate, potassium fluoride, potassium chloride, potassium bromide, potassium iodide, potassium thiocyanate, sodium sulfate, sodium thiosulfate, sodium tetraborate, magnesium sulfate, and lithium chloride. With sodium carbonate and sodium sulfite, however, emulsions were not formed, nor was there any concentration of the hydroxide a t the watertoluene interface.
D. Action of precipitated hydrous lanthanum hydroxide A sample of hydrous lanthanum hydroxide was precipitated from a hot solution of lanthanum chloride with ammonium hydroxide and washed until chloride-free. Portions of an aqueous suspension of this were placed in glass-stoppered bottles and shaken with various liquids. With ether, isoamyl alcohol, carbon tetrachloride, and chloroform there was an immediate separation into two liquid layers, and the hydroxide settled out in the water layer. With benzene, toluene, xylene, mesitylene, kerosene, gasolene, and turpentine, however, very stable emulsions were produced, and the lanthanum hydroxide was completely removed from the aqueous layer. DISCUSSION
These emulsions were of the oil-in-water type. For toluene-containing emulsions this was easily proved by treatment with small amounts of an iodine solution. The emulsions were colored pink, and closer examination revealed them to be made up of tiny pink droplets. That hydrous lanthanum hydroxide was the emulsifying agent follows not only from the fact that aqueous solutions of lanthanum salts failed to produce emulsions when shaken with the various liquids but also from the fact that the addition of small amounts of hydrochloric acid (which would dissolve the lanthanum hydroxide) immediately 'broke the emulsions, causing the separation of two liquid layers. Hydrous lanthanum hydroxide must, therefore, concentrate a t the interface between the oil and the water, and since the oil is always the dispersed phase, the hydroxide must be wetted better by water than by the organic liquid ( 5 ) . Apparently the physical character of the emulsifying agent had little to do with its action. The ability of colloidally dispersed hydrous lanthanum hydroxide to stabilize these emulsions distinguishes it from the colloidal ferric oxide reported by Briggs (1). It is also interesting to note that when mutually flocculated by colloidal gold lanthanum hydroxide loses its emulsifying power. Inasmuch as the gold is adsorbed on the floc,
HYDROUS LANTHANUM HYDROXIDE AS EMULSIFYING AQENT
263
it is probable that the lanthanum hydroxide thereby loses some of its surface activity, although such an explanation does not account for the formation of an emulsion when a sol is flocculated by various electrolytes. It is to be noted that of the liquids investigated only the hydrocarbons were emulsified. SUMMARY
1. Hydrous lanthanum hydroxide, whether
colloidally dispersed, flocculated from a sol by certain electrolytes, or precipitated from lanthanum salt solutions, stabilizes oil-in-water emulsions. The dispersed phase may be benzene, toluene, xylene, mesitylene, kerosene, gasolene, or turpentine. 2. Emulsions are not produced with ether, isoamyl alcohol, carbon tetrachloride, or chloroform. REFERENCES (1) BRIGGB: Ind. Eng. Chem. 13, 1008 (1921). (2) KLEIN:Kolloid-Z. 29,247 (1921). AND KRAUSKOPF: J. Am. Chem. SOC.60,726 (1938). (3) MOELLER (4) MOELLER AND KRAUSKOPF: J. Phys. Chem. 43,363 (1939). (5) PICKERINCI: J. Chem. SOC.91, 2001 (1907). (6) REINDERS: Kolloid-Z. 13,235 (1913).
