54 



Mr. E. P. Perman. 



[May 8, 



into the tube CD, and shaken down to the end C. Some finely- 

 divided precipitated silica was then introduced, and distributed along 

 BD. The air was expelled by heating the tube with a Bunsen's 

 burner, at the same time exhausting it by means of a water-pump ; the 

 end D was then sealed off. The tube CD was then placed inside the 

 wide tube GH, as shown in the figure ; the chlorobenzene was boiled, 

 and when the whole tube had been heated for a few minutes, the 

 projecting tube AC was rubbed with a cloth moistened with alcohol. 

 The whole tube AB vibrated, the iodine vapour in BD was thrown 

 into vibrations, and the silica on the lower part of the tube formed 

 little heaps at the nodes, and streaks perpendicular to the length of 

 the tube at the loops. The tube was then allowed to cool, withdrawn 

 from the larger tube, and placed on a horizontal millimetre scale (an 

 etched mirror scale was used). It was easier to determine the 

 position of the loops than of the nodes when silica was used. The 

 mean distance between two loops was then calculated. Similar ex- 

 periments were made with air. 



Let Zj = mean distance between two loops for air. 



Z 2 = ,, iodine vapour. 



d- = density of air. 



d 2 = ,, iodine vapour. 



7 _ S P- heat at const, press. e 



Ki lor air. 



sp. heat at const, vol. 



A; 2 = for iodine vapour. 



Then it follows from the laws of the propagation of sound that' 



Eesults.T^ was found to be (1) 35'4, '(2) 35'8, (3) 357, eleven 

 readings being taken in each experiment. The mean of (2) and (3) 

 was taken as the correct value of Z l5 these being the most trustworthy 

 experiments. The results obtained for iodine vapour are here 

 tabulated : 



