An Electrical Survey of Islands and Continents in Invisible Films on the Surface of WaterSource: The Scientific Monthly, Vol. 37, No. 5 (Nov., 1933), pp. 478-479Published by: American Association for the Advancement of ScienceStable URL: http://www.jstor.org/stable/15635 .

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478 THE SCIENTIFIC MONTHLY

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THE ONE-STORY FRAME HOSPITAL AT THE OLD FORT

To WHICH ALEXIS WAS REMOVED, ANTD WHERE HE

LAY DURING HIS LONG CONVALESCENCE.

the furtherance of knowledge in regard to the power, properties and capacity of the human Stomach.

Dr. Bernard Sachs, president of the academy, opened the meeting with a brief address, in which he related the salient points in Beaumont's unusual career. William Beaumont as an army officer was the subject of an address by Major General Robert U. Patterson.

An exhibition of books and other memorabilia relating to the life, work and travels of Beaumont will be on view at the New York Academy of Medicine until November 3.

AN ELECTRICAL SURVEY OF ISLANDS AND CONTINENTS IN INVISIBLE FILMS ON THE SURFACE OF WATER

SURFACES, or more properly interfaces, are almost all important in a study of the action of the muscles, nerves, blood and all the other parts or materials of the human body. In a research begun several years ago as supported by the Julius Stieglitz Fund of the Chemical Foundation, William D. Harkins and E. K. Fischer have begun a study of the fundamental characteristics of mem- branes, especially of the electrical rela- tions. As a part of this work the earlier methods have been modified in such a way as to enable them to give funda- mental information concerning the forces which hold molecules together, the orien- tation of molecules in thin films, and the structure of the different regions of a film.

The surfaces of all natural and arti- ficial bodies of water are covered, more or less, by exceedingly thin invisible or sub-ultra-microscopic films of oily sub- stances. These invisible films are very much thinner than those often seen, which are visible layers of oil, highly colored by interference of the light waves which traverse them, and are about 1/25,000 of an inch in thickness. It has been known for many years that elec-

trical methods may be utilized in the study of such films, but the results ob- tained were not only disappointing but conflicting. About five years ago Pro- fessor Harkins suggested that the dis- cord in the results might disappear if both electrical measurements and mea- surements of the lateral pressure of the film were made simultaneously.

It is a remarkable fact that an oil film only one molecule thick, that is, with a thickness of only about one tenth of a millionth of an inch, is capable of trans- mitting a lateral pressure which is large enough to move a floating sheet of metal, and to do this over a consid- erable number of inches. Such a film may exhibit many of the character- istics of a solid, and is then called a monomolecular or unimolecular solid film, or it may act in the two di- mensions of the surface as a liquid or as a gaseous film. The Hardy-Harkins- Langmuir theory of surfaces indicates that with films produced from oils, such as oleic or stearic acid, the molecules are oriented, as are the soldiers in a troop on parade. This orientation is most manifest when the molecules are tightly pressed together to form a condensed

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THE PROGRESS OF SCIENCE 479

film, since in this case very few mole- cules get a chance to "lie down on the surface." In gaseous films this orienta- tion is partly but not wholly preserved.

In the oil film the water-like heads of the molecules turn downward toward the surface of the water, while the oil-like tails of the molecules project upward. The electrical tests indicate that the heads of the molecules are negatively charged with respect to the more posi- tive tails.

One of the three cells of the storage battery used in an automobile gives a potential of about two volts. It is some- what remarkable that the presence of a film of oil one molecule (0.0000001 inch) thick may change the potential differ- ence at the surface by as much as about one half a volt.

The greatest practical use of the ap- paratus used in the electrical testing of a surface is to make a topographic sur- vey of a water surface. The surface potential is found to rise rapidly as the electrode, held a few millimeters above the surface, approaches the edge of an invisible island or a continent of closely packed molecules of the oil; the poten- tial remains high while the electrode is over the island, and falls again as the

APPARATUS FOR FINDING ISLANDS OF INVISIBLE FILM ON WATER

ocean of gaseous film is approached. Thus, what is invisible to the eye and to the microscope is revealed by the move- ment of the needle of the electrometer which is used to detect the change of potential. This motion is in turn shown by the movement of a beam of light.

Certain large molecules, about 60 times larger than the rather large molecules usually used to produce films, have ex- hibited the relation that they form films of only one fourth the thickness of those produced by the smaller molecules. Therefore, these large molecules, which give a film only one fiftieth of a mil- lionth of an inch in thickness, must lie flat on the surface.

RECENT DEVELOPMENTS IN THE STUDY OF CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS

WHEN alpha rays from radon or other radioactive elements pass through the molecules of substances, they ionize them by removing electrons temporarily. Chemical action frequently results and has been found to be dependent on and proportional to the number of ions formed, though the proportionality fac- tor is not the same as in Faraday's laws of electrolysis.

Similarly, if gas ions are produced in gases by electrical discharge, chem.ical action similar to that in radon is pro- duced, in the bosom of the gas, however,

not at the electrode. In different sub- stances under parallel conditions of dis- charge the amount of reaction bears the same relations as in the same reactions under alpha radiation. This leads to the assumption that the number of molecules reacting per ion is the same in both cases, though one is not able to measure nor calculate the ionization in electrical dis- charge.

Such studies have now been extended to perhaps a hundred different reactions under alpha radiation and to many more in electrical discharge. Recent investi-

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