126 Dr. Bottomley and Mr. Evans on the Measurement 



T-tube of' narrow gauge, as 



' F, to aid in the 



C was 

 3ulb F 

 water- 

 and a 

 o£ E, 



was taken and fitted with 



shown in the figure, and 



process of filling the bulb E. This apparatus was carefullj 



weighed, and it was then filled with pure 



mercury ; an extra quantity o£ mercury 



being left in the reservoir F. 



To effect the filling, the end 

 closed with a stopper, and the 

 partially filled with mercury. A 

 pump was then applied at B, 

 quantity of air was taken out 

 which bubbled up through the mercury 

 in the reservoir F. The air was now 

 allowed to flow back through B, and 

 the mercury in F was driven into 

 the bulb E. By repetitions of this 

 process the bulb E was filled, except 

 for a small bubble, which was used to 

 roll over the inside of the glass, and 

 remove adhering air-bubbles between 

 the mercury and the glass, 

 end there was no air left, 

 minute bubble at D, but there 



In the 

 except a 

 was still 



mercury remaining in 



the 



i<2cjn>\ 



an excess of 

 reservoir F. 



To get rid of the bubble at D, the 

 bulb E was cooled under the water- 

 tap ; and in this way a little more 

 mercury passed back into E, without 

 disturbing the bubble at D. By now 

 warming the bulb E with the hand, the ^s^ * 



last small bubble passed out, and a 



perfectly continuous volume of mercury was obtained. The 

 stopper at C was removed to B, and a drying-tube connected 

 at C, to prevent condensation of moisture from the air when 

 the bulb was put into ice. 



The bulb and tube, up to the level LL, were then placed 

 in melting ice, and kept there till there could be no doubt that 

 the whole was at ice-cold temperature. This being done, the 

 excess of mercury, down to the point A, was removed by 

 the application of the water-pump to B (after removing the 

 stopper) , which drew a current of dried air through the tube 

 B F A C, and cleared out the excess of mercury above the 

 point A. This method was found to act perfectly. 



The tube, with its mercury, was now very carefully dried 

 and weighed. 



