CHAPTER IV 



THE AUTOMATIC RECORD OF THE RATE OF 

 EVOLUTION OF OXYGEN 



The Automatic Recorder- — Electric Pencil with double contact — The 

 Electromagnetic Writer — Condenser for elimination of sparks — 

 Recording Drum — The Governor for variation of speed within wide 

 limits — -The Ink-Recorder — Maintenance of constancy of external 

 conditions — -Radiant point as a source of light — Ihe experimental 

 procedure — Constancy of results — -Advantages of the Automatic 

 Method. 



In order to eliminate the error due to the personal equation, 

 which necessarily attends the eye-observation of the Bubbler 

 in action, it is essential to devise a method by which the 

 periods of evolution of equal volumes of oxygen may be 

 automatically recorded. This I have been able to secure 

 by the following electromagnetic apparatus and accessories, 

 which consist of : 



(i) A Pencil with double electric contacts which com- 

 plete an electric circuit for each bubble. 



(2) An Electromagnetic Writer for inscription of the 

 record of successive periods on smoked or white paper. 



(3) A Condenser for elimination of sparks at break of 

 the circuit. 



(4) A Recording Drum. 



(5) A Governor by which the speed of the Drum may be 

 adjusted within wide limits. 



The Electric Pencil. — The successive bubbles of oxygen 

 move the oil- valve up and down through a short length. 

 A drop of mercury is placed on the oil- valve, and the 

 constriction at the end of the Bubbler is made so narrow 

 that the mercury-drop always remains above the bend and 

 does not sink into the oil forming the valve. The evolved 



