A rigorous equation is set up for the velocity of sound in gases. This is used to calculate the velocity of sound in dry air at standard conditions from data taken in independent measurements. The result of this calculation is 331.45±0.05 meters sec.−1 An extensive survey of previous reported measurements has been made. After proper corrections are taken into account, the weighted mean is 331.464±0.05 meters sec.−1 The results of very precise interferometer measurements by the authors give 331.44±0.05 meters sec.−1.
Common agricultural practices contribute to the loss of favorable soil structure. On the other hand, certain natural forces appear to contribute to the recovery of porosity and tilth. These include wetting and drying, freezing and thawing, the effects of root growth and decay, and the activity of soil organisms.In order to learn more about the nature and interplay of these forces, a method was developed for studying structural changes in buried cores of compacted soil. The technique of preparing these with various additives is described. The cores were buried under three types of cover: Forest, grass, and clean cultivation. The additives were fresh organic matter, lime and fertilizer, and an insecticide.During a 2year period the following relationships have come to light: 1. A platy structure forms as a result of wetting and drying, and plant roots tend to enter the shrink age cracks. 2. Earthworms and other small invertebrates are active in transporting and mixing the core soil with surrounding soil, particularly with added organic matter. 3. Added organic matter results in a rapid increase in aggregate stability, followed, under cultivated conditions, by a seasonally fluctuating decline. Changes take place more slowly under forest cover than in an open field. The restorative process appears to be essentially a result of the interaction of physical and biological factors. 4.
Acoustic interferometer measurements at approximately 28°C and atmospheric pressure were made from which the velocity and the absorption in CO2 were computed. Various H2O-concentrations were used with each frequency, covering the range 284 to 1595 kc/sec. At each frequency, μ (the absorption per wave-length) rises with increasing humidity to a maximum of about 0.28 and then drops slowly, but with the lower frequencies it also passes through a shelf or minor peak before saturation is reached. As the first absorption peak is approached the velocity drops about 10 m/sec. and a 1-m/sec. drop occurs near the minor peak. As the frequency is increased the critical H2O-concentration hm is increased also but at different rates for the two peaks. For the major peak fm = [60+8(10)4h] kc/sec. for the minor peak fm′ = [50+2(10)4h′] kc/sec. Thus the average lifetime of a quantum of vibrational energy is decreased rapidly with humidity. These facts are presented as graphs. They are also correlated with results by other investigators, none of whom has observed a minor absorption peak and dispersion region. Most of these facts are represented quite accurately by theory, the results of which are included.
An apparatus designed for (1) a general study of acoustical dispersion in gases, and (2) measurement of gaseous heat capacities has been used to measure the heat capacity of propylene between 273 and 490°K. The general methods used are outlined and discussed. The measured heat capacity values agree well with those calculated from the frequency assignment as given by Wilson and Wells, and an assumed potential restricting rotation of about 2000 cal./mole, but deviate from the values calculated from Pitzer's frequency assignment and an 800-cal./mole potential. The measurements on propylene also have the value of serving as a test of the usefulness and practicality of the supersonic method of heat capacity determinations.
The value and uses of supersonic velocity and absorption measurements are reviewed, and evidence that sound velocity measurements may still be used for heat capacity determinations is presented. An apparatus which is designed for (1) a general study of acoustical dispersion, and (2) the supersonic measurement of gaseous heat capacities. The general experimental technique to be used with such an apparatus is outlined, and results of measurements of the velocity of sound in air and of the heat capacity of propylene are briefly discussed.
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