INTERNAL COHESION OF LIQUIDS. 11 



have been an unbalanced tension or negative pressure equal 

 to 27 inches of mercury ; and this tension did not break the 

 continuity of the column. Hence I had a proof that the 

 cohesion within the mercury and the sulphuric acid as well 

 as the adhesion of the sulphuric acid to the mercury and 

 the glass is sufficient to resist this very considerable tension. 



Further Experiments, 



In the hope of improving the experiments, another gauge 

 was constructed, the tube being ^-^ of an inch in internal 

 diameter and 35 inches high. Into this tube mercury and 

 sulphuric acid were introduced, as in the first tube. But 

 on trying to get rid of the small bubbles of air, it was 

 found impossible to do so, as bubbles were continually 

 generated. Hence it appeared that the three weeks during 

 w hich the mercury and sulphuric acid in the first tube had 

 remained in contact had had an important influence on the 

 result. Failing in this attempt, it occurred to me to try if 

 water would answer the purpose as well as sulphuric acid. 

 Having in my possession an old vacuum-gauge with a 

 column three inches long, which had originally been wetted 

 with sulphuric acid, but into which a considerable quantity 

 of water had accidentally been introduced, I carefully 

 allowed all the air to escape, and then applied a mercurial 

 air-pump to the open end of the gauge, and exhausted as 

 far as the pump would draw. The mercury did not descend. 

 As I could apply no further tension, I shook the gauge up 

 and down ; but still the mercury remained unmoved. I 

 then tapped the gauge smartly on the side ; the mercuiy 

 then fell three inches, until it was level. Having succeeded 

 so far, I extracted the mercury and sulphuric acid from the 

 35-inch gauge and introduced some water without washing 

 the tube, and, having boiled the water in the tube, again 

 introduced the mercury. 



