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In order to clarify the best performance of sorption pump using molecular sieves, we compared the sorption rate and the sorption capacity of molecular sieves type 4A, 5A and 13X, silica gel and activated carbon respectively under the condition that the sorption pump is operated usually. Also, the pump being combined with Vaclon pump the pump, down characteristics were examined.
The results obtained in these experiments are as follows;
1) Molecular sieves type 5A is most suitable as sorption material for practical use among other kind of molecular sieves, activated carbon and silica gel.
2) Gas adsorption amount of type 5A is greatest among molecular sieves type 5A, 13X and 4A as to the gas sorption capacity, but the stability of pump down cycling is considerably inferior to type 13X.
3) The vapors of organic solvents are considered to be condensed preferentially on the sorption material independent of its pore diameter, because of their high boiling point comparing with the liquid nitrogen temperature.
4) Combination of sorption pump with Vaclon pump attained the vacuum of 2×10^-10 mmHg from atmospheric pressure without any troubles.

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A modified Nottingham gauge described in this paper has a thin gold film deposited on glass envelope as the screen electrode. Both ends of the electron collecting electrode, a cylindrical grid type, are electronically closed by a pair of wire net. The gauge sensitivity was stable and no effect of Balkhausen-Kurz oscillation was observed in the operating range while in Bayard-Alpert gauge the effect sometimes caused trouble. As this result operation of the gauge at a larger electron emission current than that for a conventional B-A gauge was proved feasible, which in turn results in practically higher sensitivity of the gauge.
Electron bombarding power required for outgassing of electrode is about 40 watt d.c.. Glass wall temperature was less than 40°C for normal operation of 0.5 milliampere electron emission. The sensitivity for nitrogen is 20.4±3, the upper limit of linearity is 4μA in ion current for nitrogen. Limit of measurement caused by soft X-ray effect was estimated to be 7×10^-11 Torr of nitrogen equivalent pressure. The ultimate pressure of zeolite trap and diffusion pump system used in this study was 2× 10^-10 Torr. Some behaviours of the system near the ultimate vacuum are also described.

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