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ortho, para ratio in the halogenation of aromatic compounds.
and drying the plate after each addition of the protein, probably because of consolidation by GEORGE HERBERT JONES M. S. KHARASCH surface tension. CHEMICAL LABORATORY E. MARCOLIS The molecular dimension (normal to the surUNIVERSITY OF CHICAGO P. C. WHITE CHICAGO, ILLINOIS F. R. MAYO face) of adsorbed molecules in a film which is only RECEIVED J U N E 18, 1937 70% complete may be determined by filling the interstices between molecules with hexadecane after covering with 4 barium stearate layers t o OPTICAL MEASUREMENT OF THE THICKNESS OF render the surface non-wettable by oil. A FILM ADSORBED FROM A SOLUTION Cooperating with Dr. Harry Sobotka we have Sir. conditioned a surface by deposition of a monoA single layer of molecules deposited from a layer of cholesterol (18 This surface takes water surface on a built-up film produces [I. digitonin from aqueous solution giving .an adLangmuir, V. J. Schaefer and D. Wrinch, Science, sorbed film of 36 A. Another layer of cholesterol 85,76430 (1937); K . B. Blodgett and I. Langmuir, can be deposited and a second adsorbed film of Phys. Rev.,51,964 (1937)] a perceptible change in digitonin, etc. These multilayers give accurate the color given by interference of light from the measurement of molecular dimensions. With Dr. E. F. Porter, we have adsorbed diphtop and bottom of the film. We can condition the surface of the built-up theria toxin on a plate conditioned by alumifilm to enable it t o adsorb organic or inorganic num chloride obtaining a monofilm of 36 A. On substances from solution, and determine the di- dipping the plate into diphtheria antitoxin, there mensions of adsorbed molecules by the change in was an increase in thickness of 75 A. Successive alternating layers of toxin-antitoxin can be built up color. Dipping the film into a solution containing a indefinitely. Not m l y the thickness but many other propersecond substance reactive to the first, a second adsorbed film can be formed. Sometimes suc- ties of adsorbed films can be measured such as contact angles with various liquids, solubilities, cessive alternating layers can be built. One method of conditioning a plate is to de- adsorbing power for substances in solution, reposit upon it an A-layer of stearic acid from a fractive index, etc. We believe the methods outlined are useful for water surface and to bring it into an aluminum chloride solution ( molar). After washing, detecting and identifying minute amounts of it is ready to adsorb many organic substances substances of biological interest and for studying the structure, reactivities and other properties of which contain polar groups. For example a drop of a 1% solution of egg al- these substances. ELECTRIC COMPANY IRVINGLANGMUIR bumin is applied to the wet plate which is then GENERAL N. Y . VINCENT J. SCHAEFER washed and dried. The apparent increase in SCHENECTADY, RECEIVED JUNE 2, 1937 thickne:s is equivalent to 2 barium stearate layers (50 A.), With Stanley’s tobacco virus protein PHENOXYPYRIDINE we obtain a maximum thickness of 12 stearate Sir : layers equivalent t o 300 A. Thanks t o Professor Chichibabin, my attention A surface conditioned by a monolayer of egg albumin deposited from a water surface takes up has been called t o some inaccuracies in a recent JOURNAL, an adsorbed film of tobacco protein having a article by Renshaw and Conn [THIS maximum thickness of only 5 stearate layers. 59, 297 (1987)], where the statement is made: This may be the thickness of molecules lying flat “A number of 2-pyridyl ethers were prepared by on the surface. Adsorbed films of other proteins heating 2-bromopyridine with the alkali salts of on aluminized surfaces give films of from 2 to 8 alcohols and phenols . , .,” and farther on: “This stearate layers. As these are not always pro- is a more satisfactory method than that reported portional to the cube root of the molecular weight, by Chichibabin [ J . Russ. Phys.-Chem. SOL.,50, some protein molecules seem to be non-spherical. 30‘ (1918)] for the preparation of 2-phenoxypyriI t facilitates the formation of a complete layer dine, the only alpha-substituted pyridine reto apply the protein in successive stages, washing ported in the literature.”
A.).
