238 SEC. 8. HEAT. 



1105b. Apparatus for keeping a Constant Temperature 



in an air or water bath. 



The Secondary Government School at As sen (Netherlands). 



This gas regulator, constructed after the design of Dr. A. Van Hasselt, 

 teacher at the school for middle-class education at Assen (Netherlands), is 

 principally made by J. Van Eossum, servant in the laboratory. 



The air thermometer, connected with the regulator and with a large Bunsen 

 cell, is partially filled with mercury, so that only the upper bulb and a 

 great part of the tube contain air. 



When the desired temperature has been acquired, the wire of platinum is 

 screwed down, so as to reach the mercury, at which moment a current from 

 the cell passes. This current passes through the wire, which is coiled round 

 the iron tube in the apparatus, through which the gas is flowing, and which is 

 used as an electro-magnet. 



The little iron valve on the side of the tube, covered with a thin plate of 

 caoutchouc, which now shuts the tube, has a small aperture, which lets pass 

 gas enough to prevent the lamp from being extinguished. 



