IReaction time the time duri *In run 42 the'aphere waa m#e by turning down a cylinder, and it waa later found that the thermocouple junction was at.0.37 of the diameter inafead of 0.50. &In run 43 O.OlO-in.-diameter wire was used, but two 1-in. sections on eaoh aide of the junction were flattened to a cross section of 0.003 in. X 0.026 in. 'In run 45 four strands of 0.001-in.Tdiam. wire were uaed fof mechanical atrength. ' In runs 40, 43, 48, and 49 the calcium, oxide was ao extepsively cracked that density figurea were not determined. The cracking in runs 39 and 45 was negIigible. *Reaction carried only to 50% completlon mark, and minunum center temperature waa not reached. Minimum was estimated at 1,677"F. 7Later in thia run a aeeond minimum of 18355°F. was obtained. The results of thia run were probably affected by extensive cracking. which gas evolution occurred.

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Below 1×10−10 Torr, pressure measurement by means of Bayard-Alpert type ion gauges is complicated by the existence of a current associated with soft ``x-rays.'' The precise measurement of a true ion current requires precise determination of the so-called x-ray limit of each gauge. The present work describes the use of a Bayard-Alpert gauge containing a modulating electrode (after the design of Redhead) to measure pressures below 10−10 Torr. Magnetron-type gauges, which do not have x-ray limitations, were then compared directly with the Bayard-Alpert gauges. In addition, gauge comparisons were carried out in a dynamic system involving pressure ratios across a capillary. Both series of experiments showed that the output current of the magnetron gauge was a power function (exponent 1.6) below approximately 2×10−10 Torr (N2). In the latter work it was possible to make measurements to below 1×10−12 Torr N2 equivalent.

of the Naval Ordnance Laboratories for their help oh the detonation velocity measurements and calculations and for the use of their facilities; and to the Office of Ordnance Research for its financial support.