The Broth of a bubble in the gap are few in spite of the many photographs of the bubble on the free expansion of the electrical discharge.
The condition of the electrical discharge in the gap, for example, we have changed inductance L, gap G, and voltage V, etc in the circuit of the R. L. C electrical discharge. And we have taken photographs of the bubble in the gap.
Our photographs showed the velocity of expansion on the groth of the bubble in the gap and the oscillation of an impulse for the bubble.
We examined this movement by the Analog Computer.
From this result we could obtain the transfer function for the movement of a bubble in the gap.

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It is found that a metal spraying process in manufacturing electrodes has an advantage of fast forming ability.
But a metal sprayed electrode has a high wear ratio in electric discharge machining.
We have developed a new method for manufacturing an EDM electrode. In this process, a shell formed by copper spraying is deoxidized in CO gas at elevated temperature, and then is precisely reformed by pressing.
The electrode manufactured in this process has a high electric conductivity and density than those of a no oxidizing and no pressing copper sprayed electrode.
Therefore, we can obtain the EDM electrodes having a low wear ratio as well as normal copper.
In the process, determination of deoxidizing condition is especially important. This paper describes a result of our experiments determining deoxidation condition.

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