In this paper, the authors treat the problem of the back streaming of oil vapour to-ward fine pressure side in an oil diffusion pump and analyse the sources in four cases : from which the back-streaming is caused : that is, (1) the drains on the jet surface, (2) the vaporization of cold oil drains on the upper wall of a pump cylinder, (3) the scattering of oil vapour stream and lastly, (4) the reflection oil vapour stream.
To measure the back streaming of oil vapour, the authors employ metal probes located in the radial direction of the cylinder at the pump head, and determine the quantity of the back streaming by the weights of the oil condensed on these probe-surfaces in the unit time.
The authors conclude experimentally that the extremely large parts of the back-streaming of oil vapour is caused by the oil drain on the jet surface, and the scattering, reflection and, evaporation of cold oil drain affects only few parts respectively, Using some baffles, the evaporation of oil from the cold surface can be measured, but the scattering and reflection are not separated each other, nevertheless, the amount of the oil back-streaming caused by the scattering and reflection is only three times as large as that caused by the evaporation from cold surface.

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The dependence of pumping speed on the nozzle was considered theoretically to obtain as completely as possible a description of the high speed oil diffusion pumps, By moans of this theory it is shown that for greated speed. There is an optimum combination for the nozzle angle and the diameter of the central tower.

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By adding a thermal electron emitter to the ordinary cold cathode Philips gauge, a high sensitive ionization gauge is expected which works with the linear characteristics at normal operating voltage where usual ion gauges are operated, An additive fine needle extended at the cylindrical axis of the hot-cathode philips type ion gauge to collect the ion current, enables one to extend its measurable range to the ultra-high-vacuum region, in accordance to the principle of Bayard-Alpert ionization gauge with greater ease, Under these considerations, we have prepared several gauge tubes and have measured their characteristics.
With such Philips-Alpert type ion gauge, the experimental results were satisfactory. The sensitivity was about 5 microamperes for the pressure p=1×10^-6 mmHg under the working condition of 600 volts to the anode, -200 volts to the repeller and the needle at a magnetic flux density of about 200 gauss. At this time the electron c current Ie was about 1 mA. The linearity was confirmed over the pressure range from 2×10^-6 to 1×10^-4mmHg, and a good stability was found.
The simpler hot-cathode Philips type ion gauge showed also a large sensitivity, but its characteristics was meager in its linearity and stability.

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[in Japanese]

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A Laboratory vacuum furnace has been constructed in order to study how to prepare the oxygen-free metals and alloys, and to develop the metallic materials used in electronic industry or any other fields which need them durable at high temperature. In this unit, melting due to either of induction and arc or resistance heating can be carried out in high vacuum or an atmosphere of hydrogen or other inert gas. And, annealing or other heat treatment in a vacuum or a controlled atmosphere and degassing of graphite or refractories are also capable in this vacuum furnace.
The chamber of the furnace has a volume of about 120 liters, and has coaxial leads which lead high frequency or other electric current for heating into the chamber, and a melt is poured by rotating the coaxial leads.
The chamber is evacuated by a 10 inches oil diffusion pump, and the pressure in it is in a range of 10^-5mmHg when a pouring of metal is ended. Induction heating is carried out by a vacuum-tube generator which has the maximum output of about 40 kilowatts and the ordinary frequency of 15 ki kilocycles per second, and the melting or casting capacity is usually about 5 lbs for nickel in case of induction melting.
On apparatus for determination of oxygen or other gases in metals has been also prepared as a belongings of this vacuum furnace at the same time. This is a modification of those which have been prepared at several laboratories in America and Europe. Like the general type of the apparatus for vacuum fusion gas analysis, it consists of three sections of gassware : a small vacuum fusion furnace, a section for extraction and measurement, and one for analysis of gases extracted. And in any section, none of, rubber, grease or oil is used, and all pumps and cutoffs are mercury ones.
The vacuum fusion furnace is a Guldner-type, and a graphite crucible used in it can be degassed at about 2500°C by induction heating from the outside of a borosilicate glass tube.

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High Voltage is supplied from the H.V. leakage transformer used for the bombardment in the evaporator vacuum vessel. The precipitation is applied only for several minutes after the start of roughing pump

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The speed of oil diffusion pump is 400l/s in case of evacuation of dry air (relative humidity almost 0%), but, in case of humid air (relative humidity almost 90100%) is decreased to 60l/s.
We cannot yet explain analytically the reason why the evacuating speed is so decreased by the humidity in air.

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