INALYTICAL EDITIOS
SEPTEMBER 15, 1940
An outline for the complete determination of sludge and sludge components is presented and recommended. S o simple relationship between gravimetric and yolumetric sludge appears to exist.
Acknowledgment The recommendations made in this article are the author's and it is not to be implied that the methods are used or recommended by The Texas Company. The author wishes to express his appreciation to The Texas Company for permission to publish the results shown in this article. Literature Cited (1) Am. Soc. Testing Materials. Glossarv. 1931. i2) A. S. T. M. Committee D-9, sud-committee IV, Section (June 17, 1931).
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(3) Beilstein, "Handbuch der organischen Chemie", Berlin, Julius Springer. (4) Damian, J., Chimie & industrie, Special No., 323-5 (1932); Rev. pholifkre, 61-2 (1933). (5) Damian, J., and Dixmier, G., Ibid., 23, 834 (1930). (6) Dixmier, G., I b i d . , Special No., 283 (1938); Ibid., Special No.. 2 7 2 4 (1929). (7) Evans, E. A., J . Inst. Petroleum Tech., 9, 384 (1923). (8) Hall, F. IT., Levin, H., and hIcMillan, W.A., ISD.ENQ.CHEM., Anal. Ed., 11, 183 (1939). (9) Holde and Eikmann, Mitt.~ ~ ~ l . l a t e r i a l p r ~ ~ ~ ~ Berlin-Lichter1Lgsamt felde West, 25, 148 (1907). (10) International Critical Tables, New York, McGraw-Hill Book Co., 1926. (11) Knutson, B., Tek. Tid., 53, (36), Kemi, (9) 49 (1923). (12) Levin, H., and Towne, C. C., IND.ESG. CHEY.,Anal Ed., 11, 181 (1939). (13) Ormandy, IT.R., and Craven, E. C., J . Inst. Petroleum Tech., 10, 101 (1924). (14) Towne, C. C., Ibid., 17, 134 (1931). (15) Woog, P., and Givaudon, J., B u l l . SOC. chim.,(4) 47, 1419-20 (1930).
Laboratory Uses for Surface-Active Agents CHESTER M .ALTER AND DEANE S. THOMAS, J R . l Boston University, Boston, Mass.
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U R I K G the past few years a large number of surfaceactive agents have become available ( 2 ) . These substances derive their claim for unusually wide interest from their ability to lower substantially the surface tension of water and aqueous solutions when present in relatively small concentrations. There are doubtless many applications of these materials in the analytical laboratory; one such use has recently appeared in the literature (1). It is the purpose of this paper to call attention to other uses which the authors have made of surface-active agents.
Quantitative Separations by Centrifuging I n the course of some experiments invoking the determination of magnesium by precipitation with 8-hydroxyquinoline, it was difficult to separate the precipitate b y means of the centrifuge. Even with relatively high speeds, small crystals of the precipitate were held at the surface of the liquid in the centrifuge tube, making it impossible to remove the supernatant liquid without removal of some of the solid. It occurred to the authors that this annoying surface phenomenon might be overcome by reducing the surface tension of the liquid. It was necessary to do this without adding any appreciable amount of foreign material that would interfere with the subsequent determination of the magnesium salt, which was to be done colorimetrically. Some of the new surface-active agents were tried and found successful for this purpose. The direct addition of one drop of Tergitol 7 (manufactured b y the Carbide and Carbon Chemicals Corporation) to the centrifuge tube containing 10 ml. of the suspended magnesium salt was sufficient to cause the solid to be completely settled by slight centrifugation. It is apparent that the procedure outlined above is applicable to many analytical methods. It should be especially helpful in microanalytical work where quantitative separation by centrifugation is very often used. One of the authors has found it often applicable in routine separations in semimicromethods of qualitative analysis. 1
Present address, Eastman Kodak Company, Rochester,
N.Y
Creeping Precipitates Certain finely divided precipitates handled in quantitative analysis have a tendency to creep u p the walls of the container causing annoyance and possible error in many analytical procedures. Calcium oxalate is especially offensive in this respect. If the surface tension of the solution is lowered by the addition of a surface-active agent such as one of the Tergitols, this difficulty is remarkably decreased. If the agent is added previous to the time of precipitation, crystal growth is inhibited by the adsorption of the large polar molecule. A precipitate of calcium oxalate thus formed will pass through the ordinary quantitative filter paper. If the agent is added after precipitation and digestion, the particles of precipitate mill remain large and easily filterable, the c r e e p ing tendency is almost completely overcome, and transfer of the precipitate is easily accomplished. The concentration of Tergitol necessary is not great enough t o cause appreciable error in the ordinary determination of calcium if gravimetric methods are to be used. If the volumetric method is used for the determination of the calcium oxalate, no error should be expected. Stabilizing Suspensions I n nephelometric and turbidimetric analysis one of the experimental difficulties encountered is the settling of the suspensions. Often it is desirable to stabilize such suspensions in order to make consistent determinations. Some of the surface-active agents are particularly well adapted for this purpose, since they are active in such low concentrationsfor instance, the life of a silver chloride opalescence as used in nephelometric measurements is increased twenty fold by the addition of a small amount of Tergitol. There are doubtless many other applications of such materials in the laboratory, but these three mill suffice to indicate that surface-active agents are useful reagents to keep on the laboratory shelf. Literature Cited (1) Roberts, C. H. M., IND. ENQ.CHEN.,Anal. Ed., 10, 518 (1938). (2) Van Antwerpen, F. J., IND. ENQ.CHEN.,31,66 (1939).
