The Effects of Power Level on the Microwave Heating of Selected Chemicals and Minerals

ABSTRACTThe effect of power level on the microwave heating characteristics of a variety of reagent-grade chemicals and minerals has been determined in a Bureau of Mines study. Heating rates of the powdered samples are presented for incident power ranging from 500 to 2,000 W at 2.45 GHz. The apparatus consisted of a WR 975 waveguide-applicator mounted to WR 284 waveguide sections and connected to a 3-kW power source. Tests were conducted in an alumina crucible enclosed in a fused-quartz beaker that was fitted with a Teflon lid to allow for a controlled inert atmosphere and thermocouple insertion. In general, heating rates increased as input power increased. Exceptions to this were some very high-lossy (microwave receptive) and very low-lossy materials that showed negligible changes with increased power. Microwave data collected should provide insight as to possible chemical and mineral processing applications as well as to assist in predictions of processing parameters.

Studies on the biological action of light

Section I.—The Effect of Light on the Metabolic Rate of Small Animals. Introduction .—Whereas plant life is directly dependent on the supply of radiant energy from the sun or an artificial source of light, animals may lead perfectly healthy lives in complete darkness. Early observations by K. A. Hasselbalch on the total metabolic changes in experimental animals, and by A. Durig and his co-workers on the respiratory exchange in man, seemed to show that light was without action on animal metabolism. Recently, however, the therapeutic application of sunlight at Alton and Leysin (1) and the radiations of the large carbon arc in the hospitals of our large towns have yielded results which suggest a stimulant action on general metabolism. Measurements by Leonard Hill and A. C. Campbell (2), however, show that the open-air conditions were mainly responsible at the former resorts. The present investigation of the gaseous metabolism of small animals supplies an approximate measurement of the total metabolism during exposure to artificial radiations. Method .—The rat was the species chosen as it could be comfortably confined in a small quartz beaker used as a respiration chamber. The latter was fitted up in a manner somewhat similar to the arrangement in the Haldane-Pembrey respiration apparatus.