Measurements on the Gases Evolved from Glasses of Known Chemical Composition

T h i s paper has a very direct bearing upon the p u m p i n g or exhausting of the v a c u u m tubes used in telephone repeaters a n d similar thermionic tubes. T h e telephone repeater b u l b , as is well k n o w n , holds a v a c u u m of the order of 10= 6 m m . of mercury. In order to produce this v a c u u m it is necessary d u r i n g the m a n u f a c t u r e of the t u b e to not o n l y remove the air from the space w i t h i n the b u l b b u t also to allow very considerable a m o u n t s of various gases to diffuse o u t from w i t h i n the glass of the b u l b a n d the metal parts of the t u b e structure. T h e v o l u m e of gas which is frequently removed from the m e t a l plates, for instance, m a y be roughly estimated as 100 times the v o l u m e of the plates themselves, the v o l u m e of the gas being measured at atmospheric pressure. To remove these gases from the b u l b a n d metal parts, it is necessary to m a i n t a i n d u r i n g the p u m p i n g process a temperature which is far a b o v e the n o r m a l temperature a n d a fair degree of v a c u u m w i t h i n t h e b u l b for a period of time which varies from a few minutes to an hour or more depending u p o n the t y p e of t u b e . W i t h a view to simplifying the p u m p i n g process, the authors have found t h a t a glass relatively free from absorbed gases can be produced by using special precautions in manufacture. T h e a u t h o r s have also measured a n d analyzed the gases evolved from glasses of various composition.