pletely exhausted that no trace of gas is apparent, and yet as soon as the filament is lighted there might be plenty of evidence that the tuhe contains gas-the presence of gas being indicated by a bluish haze within the tube. The metal and glass absorb large amounts of gas and water vapor, and added quantities stick to the surfaces. The hubhles, driven out by the heat from the tube filament, must be expelled from both the glass and metal parts of the tuhe. It is not possible to subject the glass to anywhere near as high a temperature as the metal parts require. The high frequency furnace solves the problem. While the tuhe is being exhausted i t is kept a t as high a temperature as the glass will withstand without softening and collapsing, hut this temperature is not sufficient to boil the gas and moisture from the metal parts. Just before the radio tube is sealed from the vacuum pump i t is placed for a moment within a high-frequency coil. The metal parts immediately become red hot and the bubbles of gas and vapor are boiled out. The tuhe is then sealed from the pump, with the knowledge that later heating of the tube by the filament will not cause further release of bubbles. In this age of machinery, it almost necessarily follows that the high frequency induction heating of the tubes is automatic. Just before the tuhe is sealed from the pump, a high-frequency coil on the end of a mechanical arm automatically descends over the tuhe, and for a few moments the tube is subjected to the field of the coil. The metal parts glow, the gas bubbles escape and are removed by the pump, the coil is automatically removed, and the tube is ready for the sealing process. The high frequency furnace used in vacuum tube work would hardly he recognized as a furnace. It is simply a coil of copper conductor attached to a wooden handle, drawing its power from a nearby metal cage on wheels. Within the cage is the equipment for changing the ordinary 60-cycle power to oscillatory current of the desired frequency. It includes a step-up transformer, a couple of radiotrons, and a bank of high-voltage mica condensers. High frequency and high vacuum-millions of cycles and millionths of an atmosphere--are two requisites of vacuum tuhe production which research has provided.
New Use Found for Wood Alcohol Waste. Lactic acid, a chemical which has numerous industrial uses, can be made from the waste in the manufacture of wood alcohol, members of the American Chemical Society were told by E. G . Sharrard, of the Forest Products Laboratory of Madison, Wis. The work was done in collaboration with W. H. Peterson, E. B. Fred, and E. A. Martin. The wood sugar liquor remaining after the alcohol manufacture, ahich was formerly discarded, is treated with nitrogen and calcium carbonate to produce the lactic acid.-Science Semice
