(510 Scientific Proceedings, Royal Dublin Society. 



II. — Temperature Control. 



In the experiments previously recorded the temperature of the apparatus 

 was maintained constant by providing a large reservoir of water, and allowing 

 the water to run through the water-jacket of the apparatus while the observa- 

 tions were being made. This method only allowed of the maintenance of a 

 steady temperature for a few hours, and experiments could not be repeated 

 at the same temperature at will, nor could higher temperatures than that of 

 the room be obtained. 



In order to bring the temperature under control, it was decided to use, a 

 thermostat, and circulate the water from it through the water-jacket of the 

 apparatus. To provide the circulation of water a small centrifugal pump was 

 designed, patterns were made and castings obtained from the Engineering 

 Department of the College, while the machining was completed in the work- 

 shop attached to the Chemical Department. 



This pump maintained a rapid stream of water through the water-jacket 

 at a constant rate ; and no difficulty was experienced in keeping the tem- 

 perature constant to within - l°C. A further advantage was that any desired 

 temperature within fairly wide limits could be attained, and experiments 

 could be repeated as often as desired at the same temperature on different 

 days. 



III. — Experiments to determine the effect of the Area of the Bubble 



ON THE EATE OF SOLUTION. 



(a) Measurement of the lengths of different hibhles in motion. 



Bubbles of five different volumes were measured at 25° C. while in motion 

 up the tube. Arrangements were made for photographing each bubble and 

 the scale in close proximity to each other, through the water-jacket, by pro- 

 viding a scale ruled on thin tracing-paper, and cementing this to the inner 

 tube with Canada balsam. This scale was almost transparent, and the image 

 of the bubble was orthographically projected on to it by means of a beam of 

 parallel light from, an arc lamp. The camera was focussed sharply on the 

 scale, and the shutter was released just as the bubble passed behind the scale, 

 so that on the negative the scale lines were superimposed upon the image of 

 the bubble. 



These negatives were measured by means of a travelling microscope, and 

 the measurements referred to the paper scale, the errors of which were deter- 

 mined by means of a standard scale both before and after use. The length of 

 each bubble, when at rest, was measured with a mirror scale, which was also 



