INDUSTRIAL AND ENGINEERING CHEMISTRY
740
Measurement of Contact Angles Methods which have proved most practical for the measurement of contact angles formed by liquids against solids are as follows: sessile drop (4, I d ) , bubble ( I S ) , pressure of displacement ( 7 ) , tilting plate (I), capillary ascension, and vertical rod (6). The first three methods are believed t o be most suitable for the majority of systems. The sessile drop and bubble methods are similar in principle; they are direct methods with which drops or bubbles in contact with a surface can be continuously observed; drops and bubbles can be easily photographed and the angles readily measured. Pressure of displacement is the only known method that can be used when the solid is in a finely divided condition. The method is indirect. It is time consuming, and requires considerable experience, a high degree of skill, and much patience. It is recommended only for those cases where the solid is such that one of the other methods mentioned cannot be used. The tilting plate and vertical rod methods are of practical importance in that they offer the only means suitable for use with solid materials in the form of small rods, wires, and fibers. They offer promise for research in textiles. The capillary tube method, while of fundamental importance, appears to be of limited value for practical purposes.
Reproducibility of Contact Angles
Vol. 33, No. 6
obtain reproducible surfaces by a vaporization in vacuo method. Different metals, sulfides, and other substances have been used in the formation of solid films, the surfaces of which could be studied by contact angle methods. The results have been gratifying, and contact angle values of a given liquid upon different samples of the same solid have shown agreement within 1’. The contact angle method used was the sessile drop msthod. The drop of liquid formed on the solid surface was connected by a liquid column with a mercury reservoir. Movement of liquid was controlled by a small-diameter screw piston fitted into the mercury reservoir, Figure 4 ( 5 ) . The success of the method lies in the fact that movement of the liquid used to form the drop can be kept under exact control so that either advancing or receding angles can be maintained for indefinite periods and can be measured a t will. Within the past year thousands of measurements have been made with this method, and the results have been so promising that a number of different researches are now under way. I n one of these an attempt is being made to evaluate the efficacy of different wetting agents and to determine the specific effect of substitution of different radicals and groups into the molecule of the wetting agent.
Literature Cited (1) Adam, “Physics and Chemistry of Surfaces”, p. 147 (1930); “Wetting and Detergency” (1937). (2) Andreas, Hauser, and Tucker, J. Phys. Chem., 42, 1001 (1938). 13) Bartell and Bartell. J . A m . Chem. Soc.. 56. 2205 119341. ’ (4j Bartell and Bristol; J . P h y s . Chem., 44, 86 (1940). (5) Bartell and Cardwell, I b i d . , t o be published. (6) Bartell, Miller, and Culbertson, I b i d . , 40, 863 (1936). ENG.CHEM.,19, 1277 (1927). (7) Bartell and Osterhof, IND. (8) Harkins, J . Am. Chem. SOC.,39, 354, 541 (1917). (9) Hauser, Edgerton, Halt, and Cox, J . Phys. Chem., 4 0 , 973, (1936). (10) Langmuir, Chem. K! Met. Eng., 15, 468 (1916); J. A m . Chem. Soc., 39, 1848 (1917). (11) McBain, J . A m . Chem. Soc., 62,419 (1940). (12) Mack, J . Phys. Chem., 40, 869 (1936). (13) Wark, “Principles of Flotation”, Melbourne, Australasian Inst. of Mining and Metallurgy, 1938. ~~
A careful study of contact angle values found in the literature discloses the fact that different investigators seldom obtain values which are in agreement. About the only exceptions are the values obtained with soft organophilic solids, such as paraffin. I n fact, seldom has any one investigator been able to obtain closely reproducible values for different surfaces of a given material. Recent investigations have made it almost certain that the cause for this lack of agreement has been, not so much defects in methods of measurement, as the fact that insufficient care had been exercised in the preparation of surfaces to ensure that they would have identical properties. I n recent work in this laboratory we have attempted to
PRESENTED before the American Section of the Society of Chemical Industry, New York. N. Y .
Surface-Active Agents-Additions
and Corrections
A few errors have been pointed out in the table of surface-active agents manufactured in America and commercially available, which appeared on pages 16 to 22 of the January, 1941, number The following additions are also made by F: J. Van Antwerpen who compiled the table : Industry
Use
Name Calgon
Sodium hexametaphosphate
ADDITIONS Dispersing, deflocculating mater generating, textile
Cresol
CaH50H-CH3
Wetting
Cyclohexanol Methylcyclohexanol Pyridine Quadrafos
Hydrogenated phenol Hydrogenated m,p-cresol GH5N Sodium tetraphosphate
Textile, general degreasing Wetting, detergent Same Same Textile Detergent Dispersing, detergent aid, Textile, water generating deflocculating
Alkanol S
Sodium tetrahydronaphthalene sulfonate Purified suifolignin Processed waste sulfite liquor
Dispersing
Textile, soap
Dispersing in water Dispersing, flushing
Latex, pigment, textile Same
Textile
Manufacturer Calgon Inc., 300 Ross St., Pittsburgh, Penna. Barrett Co., 40 Rector St., New York, N. Y . Same Same Same Rumford Chemical Works, Rumford, R. I.
ERRATA
Dilex Hornkem
E. I. du Pont de Nemours & Co., Inc. Horn Research Labs., Inc. Same
