7Y//r .lI.K.ll.l Mlil.ll. I'llOrOELF.CTRIC CELL 



333 



part. The next step is to introduce a small amount of pure hydrogen 

 gas, which is permitted to enter from a reser\-oir on the system. This 

 hydrogen gas goes through the system of bulbs through which the 

 potassium has been distilled, whicli still contain a large amount of 

 potassium, and is thereby cleaned of all traces of gases or vapors which 

 might react on the potassium in the cell. A glow discharge is then 



'iZO 100 80 60 40 20 20 40 60 60 lOO IZO i4D 



+ 



VQLTAGF ONPOTASGIUM 



Fig. 12 — Typical voltage current characteristic of potassium photoelectric cell as 

 used in picture transmission. Incident luminous flux = .015 lumen. 



