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The radioactive elements emit rays which are able to affect the photographic plate and it is possible to determine by contact exposure the approximate concentration-distribution of the element in flat sections of plant or animal material, sometimes locating boundaries within a few microns. These exposures are called radioautographs (or more simply autographs). As the different elements vary over a wide range in regard to the nature and intensity of their radiation, the conditions for proper exposure of the plate vary correspondingly. Hamilton states (7) that bombardment by 2 ? IO6 beta particles of at least 0.15 M.E.V. average energy per sq. cm. plate surface is necessary for production of a satisfactory image. X-ray film gives the most rapid results but if it is necessary to magnify the autograph considerably, the graininess of the film is objectionable and slower; fine-grained film should be used instead if possible. Radioautographs of animal structures have been prepared using phosphorus* (12),2 iodine* (8) and others. Hamilton, Soley, and Eichorn (8) in a study of the iodine* content of goiter tissue, made paraffin sections of the tissue, removed the paraffin, and dipped the sections in a dilute solution of collodion which was allowed to dry. The sections were then placed in contact with the film separated only by a layer of collodion approximately one micron thick. Arnon, Stout, and Sipos (1) and also Colwell (6)3 have investigated translocation in plants, partly by means of autographs using radiophosphorus. The activity of radiophosphorus is so great that it is possible to obtain good autographs through several layers of paper after exposures as short as one hour. Autographs employing sulphur* have not been found in the literature. Sulphur* radiation has only about one-fourteenth the energy of phosphorus* radiation and special precautions are necessary to avoid absorption of the former before it reaches the plate. Particularly, it is necessary to place the film in close contact with the sections, with a minimum of intervening material which might absorb a portion of the emanating rays. This paper completes the observations described in the preceding paper (16) by submitting autographs to show the distribution of the sulphur* in the spring wheat.

Some data on photosynthesis and respiration rates for alfalfa fumigated with SO/sub 2/ are examined for compliance with Stoklasa's invisible injury theory. It is suggested that invisible injury attends to a very limited extent the reducing conditions characterizing SO/sub 2/ fumigations. Other data suggest that the oxidizing conditions in smog seem to be more effective in causing invisible injury.

Those aspects of air pollution that are of major interest to agriculture are summarized. Reference is made particularly to sulfur dioxide, fluorine compounds, and smog. Substances of minor interest are not considered. 39 references, 1 table.

The apparatus and experimental technique which are described in this paper have been developed to determine continuously, automatically, and throughout the life of a plant, if desired, the carbon dioxide exchange and the transpiration in a chamber in which plants are growing under field conditions. This discussion gives a general resume of our methods, including, first, a description of the equipment ; second, illustrations of its application to alfalfa and wheat ; third, a statistical analysis of the data, showing the magnitude of the errors and variability involved ; and fourth, some interesting observations on the relation of light intensity and temperature to the rate of photosynthesis, respiration, and transpiration, which these methods have made clear.

Radioactive sulphur (S35) with its weak beta radiation of 0.120 M.E.V. and its long half-life of 87 to 88 days (6, 8) has desirable characteristics as a biological tracer, particularly since its activity can be readily measured after recovery as barium sulphate (6). Further, as will be shown in the following paper (5), excellent autographs of thin sections of plant material can be made on photographic film. Seaborg (9) and Hamilton (3, 4) have reviewed the literature up to 1941 on the use of radioactive elements as tracers in chemical and biological work. Radiosulphur in synthetic cystine, methionine, and thiamin as well as inorganic compounds, has been used in nutritional studies of animals (1,10), but so far as is known, nutritional studies of plants using radiosulphur have not been reported. This paper describes experiments carried out in 1942 with radiosulphur furnished as barium sulphate*2 by Dr. J. G. Hamilton of the Radiation Laboratory, University of California. The sulphur* was added to vegetation growing in the large sand cultures (13) both as a soluble sulphate* in the nutrient solution and as sulphur* dioxide in the air. No radiosulphur was available during the 1943 season.

A portable gas dilution apparatus has been constructed by which reproducible known mixtures of the common air pollutants added to carbon filtered air can be prepared in any desired quantity, complexity, and concentration. Sulfur dioxide mixtures with and without the addition of nitrogen dioxide and/or ozone have been analyzed by the conductimetric, titrimetric, turbidimetric, and colorimetric methods. Excellent analytical agreement with the concentrations obtained from the volumes of sulfur dioxide, nitrogen dioxide, hydrogen sulflde, and air that are mixed has been shown by all these methods when an efficient absorber is used though the titrimetric method tended to give slightly low results. Some common absorbers show reduced efficiency in absorbing some of the gases. Nitrogen dioxide determinations by the Saltzman method are not significantly affected by the addition of sulfur dioxide to the nitrogen dioxide-air mixtures. A modification of the Saltzman reagent, due to Lyshkow, was tested. It accelerates...

Interest in air pollution is increasing. This is the second of I and EC's biennial review of significant developments in this field. New analytical methods and instruments for both gases and aerosis have appeared. Among the unique developments for removing pollutants at the source are high temperature filtration of open-hearth gases through slag wool filters, and the use of the Hersey reverse-jet bag filter in the atomic energy field. Chemistry of the Los Angeles smog, the auto exhaust problem, and air pollution and its relation to health have all been areas of active research. 96 references.

The chemical nature of the two basic kinds of smog is defined. Sampling programs for urban areas are described. The types of symptoms caused by pollutants are discussed. Among those treated are eye irritants, ozone and plant toxicants, carcinogenic compounds, and respiratory irritants. An epidemiological approach to study of chronic air pollution problems is briefly discussed. 21 references.