NEW BOOKS to 4 χ 1010 ergs per gram carbon. Further investigation is recommended to develop the systems. Calibration, reproducibility, sensitivity to impuri ties, dose rate dependence, and irradi ation to higher dose levels are facts which should be considered. Molecular Weight Determination in the Characterization of Polymers.
R. M. Lange, Wright Air Develop ment Division, U. S. Air Force. PB 171401. September I960. 28 pages. 75 cents.
DEPENDABLE ACCURACY Wavelength: 5A Photometric: 0.005 at 4A CRITICAL REPEATABILITY Wavelength: 2A Photometric: 0.003 PRACTICAL WAVELENGTH RANGE
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The Spectronic 505 provides high-speed, high-precision recording of transmittance, linear absorbance and emission—plus ac cessories for reflectance between 400-700 RAPID SCANNING χημ. The only other instruments that can 6 different speeds, from approach its speed, accuracy and simplicity approximately 1 minute cost from two to four times more. That's to 10 minutes why the Spectronic 505 has become the 1 best-selling spectrophotometer of all time. BAUSCH & LOMB INCORPORATED 0.1% at220mu
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ANALYTICAL CHEMISTRY
Preliminary results and recommenda tions for future study are given on the determination of the molecular weight of poly-(dimethyl-2 ; 2-dimethylene pimelate) prepared by solution polymeri zation to 40% conversion. Techniques used in the study included osmometry, light-scattering, viscometry and frac tional precipitation. Osmotic pressure measurements on a sample of the whole polymer in toluene solution gave a number-average molecular weight of 3.36 X 10s grams/mole. Some light-scattering measurements showed a weight-average molecular weight of 2.80 X 106 grams/mole. The heterogeneity index (M w /M n ) indi cated a broad distribution of molecu lar weights. It was recommended that in future light-scattering studies cy lindrical cells rather than semi-octag onal cells be used and that equipment be developed for determining the weight-average molecular weight of very small quantities of material in the range of 0.010-0.500 gram. Theoretical and Experimental In vestigation of Radioactive Ion ization Gauges. M. A. El-Moslimany, University 0} Michigan, for Air Research and Development Com mand. PB 171 105. May I960. 183 pages. $3.00. As part of a systematic study of radioactive ionization gages, the chief ionic and electronic processes encoun tered are briefly reviewed. A relation ship between the collected ion current and the gas pressure is analytically de veloped for a planar configuration, considering the probability of electron attachment as a function of the elec tric field intensity and the gas pres sure. In calculating the theoretical current-pressure curves, the numerical values used for ionic mobilities and the recombination coefficient are those used for different mixtures of nitrogen and oxygen. Experimental current-pres sure curves are found to be in fair agreement with the theoretical results. Two radioactive ionization gauges were
