392 



Scientific Proceedings, Royal Dublin Society. 



C* 



an inner tube, about 1 metre long, and 1 cm. bore. Into each end of the 

 tube a rubber stopper is fitted. The lower stopper carries a 

 m small capillary stopcock, and the upper one, a two-way stop- 

 cock, with capillary tubes. One limb of this tap was cut off 

 short, and inserted in the stopper. Of the two other limbs one 

 was left straight, and cut off short, while the other was bent 

 over until parallel with the long tube, and a length of fairly 

 wide capillary tubing was fused on to it. The lower end of 

 this tube was connected by rubber tubing with the movable 

 limb of the manometer, which was also provided with a stop- 

 cock, to prevent the liquid spilling when inverted. This 

 I I ■"- Z. manometer was filled with water, coloured with a little 



I \r- ~ methylene blue. 



I The long tube was completely surrounded by an outer 



If; jacket, held in place by rubber stoppers, which were provided 



I I - - with inlet and outlet tubes for a current of water. 



V^ ■"- - A mark B was made on the manometer tube to which the 



level of the meniscus was always brought when taking a 

 reading, and the volume of the space between this mark and 

 the stopcock was measured by filling with mercury and 

 weighing the mercury. This small volume involved a constant 

 correction, which had to be applied to the observed manometer 

 readings in order to get the true pressure in the tube. 



Fio. 3. 



1_ 



If p' = loss in pressure in bubble, 



pi = loss in pressure measured on manometer, 

 v = volume of capillary, 

 V = volume of bubble, 



then p' and jh are connected by the formula 



P=pA l + 



The experimental tube was filled with the air-free water by exhausting 

 it as completely as possible by means of a water-pump, and then attaching 

 it to the vessel containing the air-free water. By opening the connecting 

 tap, and allowing air to flow into the vessel containing the supply of distilled 

 water, the tube was filled, almost completely, without allowing the water to 

 come into contact with air. The small bubble left at the top was removed 

 by taking out the rubber stopper, and quickly filling up the space with air- 

 free water from a pipette, and allowing it to overflow. The cork was then 





