1073 



same action as the small quantities of phosphorus that are necessary 

 (o remove the rest-gases. 



§ 3. Oil th.e condensale, formed by the vaporizotion of very 



siuall qutfutities of silicate. Prevention of the blackening 



of the bulb loall. 



In our expei'iments with the glass capillary we have seen, that 

 from the glass prinei|)allj only the alcaline-oxides are found on the 

 wall. In the technical glow-lamp this is however not the case. There 

 the quantity of glass powder on the incandescent body that is 

 required, is so small, that in a moment everything has passed to the 

 wall, where the precipitate has again a neutral character. Another 

 question however is, whether the glass formed in this way on the 

 wall, is the same as that which covered the incandescent body. 

 Though the whole pi'ocess lasts vei'j shoi-f, still the sublimation 

 must have been fractional and the cooling down must have taken 

 place exceedingly rapidly. In fact the glass on the wall is different. 

 Perhaps it consists of different layers of different constitution. At 

 all events the alcalines are bound more loosely. They are solved 

 more easily than the alcaline tVom the original glass. When the 

 lamp is subjected to 7ks/a-discharges a sharp flashing of the wall 

 is oberved. Spectroscopically the sodium-lines are seen very intensive. 

 With ordinary glass this is not the case. Under special conditions 

 crystallization may take place, when the lamp is opened. Analogous 

 changes form a separate dominion of investigation ^). 



Besides the removal of the rest-gases from the glow-lamp the glass 

 that covered originally the incandescent body exerts still another 

 action. We have seen above how by the condensation on the bnlb- 

 wall no "normal" glass is obtained. P. P. von Weimarn ^) already 

 has remarked that the specific weight of the glass is smaller according 

 as it is cooled more rapidly. The distances of the molecules in 

 such a glass would therefore be much greater than in the normal 

 glass. In these proceedings Messrs. L. Hamburger, G. Holst, D. Lki,y Jr. 

 and E. Oostkrhuis have published a communication, in which it is 

 investigated, how certain solid substances, when applied in a thin 

 layer on the buHvwall, can |)i'event the darkening of the wall (a 

 consequence of the condensation of vaporized tnngsten from the 

 incandescent filament). This decolorating action is proved to have a 



1) W. Reindkrs and L. Hambukgkr. These Proceedings 25, 661 (1916 >, 26, 

 595 (1917). 



-) P. P. vuN Weimarn, Zeitschr. f. Gliein. u. Ind. d. Koll, 9, 25 (1911). 



