Evaporation of different Liquids at their Boiling-points. 41 



the lamp was condensed in the jacket, and there was no loss 

 of material. 



The two lamps were connected in series. 



In the earlier experiments the current used was that sup- 

 plied at 110 volts to run two incandescence-lamps of 32-candle 

 power (in parallel) : it was further cut down to a convenient 

 strength by the introduction of an appropriate resistance. At 

 first this resistance consisted of a solution of copper sulphate 

 — therefore both indefinite and variable : in the later experi- 

 ments a coil of wire of about 20-ohms resistance was substituted 

 for the copper-sulphate solution. 



In. performing an experiment, the liquid in the side-bulb 

 of the jacket was first caused to boil ; and the current was 

 not started until the whole contents of the lamp were judged 

 to have reached the temperature of the condensing vapour : 

 if this were so, the liquid would pass into tranquil ebullition 

 the moment the circuit was completed. It was generally 

 found advisable to drop into the lamp a little glass capillary 

 tube to provide a starting-point for boiling, as most of the 

 liquids snowed a great tendency to become superheated and 

 bump. A number of experiments were rejected for this 

 reason. 



5. Preliminary Experiments. February 1894. 



In the experiments with carbon lamps, the resistance of 

 each filament was determined by the Wheatstone-bridge 

 method, using a post-office box of coils for bridge, at five 

 different temperatures ; and the results were plotted on 

 squared paper. The observations for each lamp lie approxi- 

 mately on a straight line, the resistance falling off uniformly 

 as the temperature rises. 



The resistance of each filament at 0° and 180°, the decrease 

 per degree, and the coefficient of change of resistance between 

 0° and 180° were found from the curves. 



Table I. 





I. 



II. 



III. 



Resistance at 0° 



42-5 ohms. 

 36-69 „ 

 00323 

 0-00076 



4317 



36-58 



00366 



0-00085 



42-60 



3610 

 00361 

 0-00085 



Resistance at 180° 



Decrease per degree 



Coefficient of change of resistance... 



These experiments gave no satisfactory results. 



