Third Report of the Committee on Photochemistry Reprint and Circular Series of the National Research Council (1938) / Chapter Skim
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Experimental Techniques in Photochemistry
Experimental Techniques in Photochemistry
Pages 3-14
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From page 3... ...
It is planned merely to build on the first report giving trends of the past decade in experimental photochemistry, to record advances in technique, and to refer to a few selected researches where further details and additional references may be found. LIGHT SOURCES Arcs The quartz mercur~vapor arc lamp is the almost universal standard for photochemical investigations when monochromatic light is necessary.
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From page 4... ...
Neon lamps are also available in convenient form for producing red light, but it is difficult to obtain a highly concentrated radiation from a small area of these lamps. Quartz capillary lamps of cadmium, zinc, thallium, bismuth, and lead can be made to give light at several different lines which is practically as intense as that of the capillary mercury lamp.
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From page 5... ...
A different composition will pass light of a different wave length. Close temperature control is essential and the range of wave lengths transmitted is not as narrow as might be desired, but the filter can be adjusted to any wave length and the loss of energy in the transmitted light is not great.
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From page 6... ...
Large-area thermopiles which do their own integrating are simpler for photochemical investigations. The thermocouples, thoroughly protected with glyptal lacquer, are attached with de Khotinsky cement to the back of a blackened receiver 10 by 40 mm.
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From page 7... ...
In the study of ultraviolet radiation of extremely low intensity, Geiger counters are used in which a photoelectric surface emits electrons into a gas space between charged electrodes. A system of electron tubes amplifies greatly the ionization current produced each time that a photoelectron is shot out.
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From page 8... ...
CHEMICAL ANALYSIS The requirements for monochromatic light reduce the energy intensity to such an extent that micro or semi-micro methods of analysis are often necessary. One of the most successful micromethods for gas analysis has been developed by Blacet and Leighton (2, 3, 4)
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From page 9... ...
Special techniques have been developed. It is a good plan to have the thermopile back of the heated reaction chamber completely immersed in water to prevent radiations from the heated walls striking the thermopile.
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From page 10... ...
The fine structure of the spectrum of acetone vapor offers an illustration (38, 39~. The more complex organic compounds and substances in the liquid phase are not likely to show fine structure, but a complete knowledge of the various absorption bands is helpful.
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From page 11... ...
has described a delicately balanced colorimeter, with an amplifying circuit of electron tubes, which measures with great accuracy the change in absorption produced by a photochemical reaction. The conversion of ortho-para hydrogen has been used also as a test for the independent existence of free radicals containing an odd number of electrons (51~.
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From page 12... ...
Interesting developments are to be expected in photochemical studies at high and low temperatures, and at low gas pressures. Greater accuracy in determining quantum yields is useless unless the conditions of temperature, pressure or concentration, and light intensity are clearly defined.
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From page 13... ...
(44) RICE AND RICE: The Aliphatic Free Radicals.
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