Phosphorus Tube.
Messrs. Siemens and Halske manufactured a tube which allowed of a slight variation of vacuum by using the vapor of phosphorus. An auxiliary tube containing phosphorus was added to the main tube, and upon heat being applied to it by means of a lamp, vapor is given off, which materially reduces the vacuum of the main tube. When the opposite result is desired part of the current is diverted through the auxiliary tube, and the vapor is caused to solidify itself upon the walls of the tube.
Fig. 73.