OP ARTS AND SCIENCES. 6 



bulb at Z), the entrance to the capillary. Both inner and outer oil 

 baths are continuously stirred by an agitator moved to and fro through 

 the troughs by a water motor with connections not shown in the sketch. 

 This arrangement maintained temperatures as high as 225° constant 

 within about 0°.5 in most measurements, and so nearly uniform 

 throughout the tiough that no perceptible difference could be found at 

 various points along the capillary. A thermometer at aS in the outer 

 bath served to adjust the lamps so that their heating should be such as 

 to maintain a nearly constant temperature. Automatic thermo-regula- 

 tors were tried, but were found in general to be quite as much of a dis- 

 advantage as benefit, and were abandoned. 



The details of the apparatus will be described, beginning at the point 

 where the gas enters. When air was used, the laboratory air was 

 drawn in through caustic potash to remove the carbonic acid, and 

 through concentrated sulphuric acid, fused chloride of calcium, and 

 anhydrous phosphoric acid in the tubes ^and T, which are further de- 

 scribed at I. 2, p. 29. When carbonic acid was used, the gas was formed 

 by the action of hydrochloric acid on marble, was purified by washing 

 in water, dried, and freed from hydrochloric acid by passing through 

 tubes of pumice coated with anhydrous copper sulphate. The gas was 

 then drawn through P into ,/ by withdrawing the concentrated sul- 

 phuric acid from ./into K, as about to be described, and was there held 

 for use. When a measurement was in progress, the gas in /, being 



