370 Prof. Partington and Mr. Cant on the Specific Heats 



sound of the same frequency can then be determined in the 

 gas and in air. 



In the experiments described below a gas tube was used 

 which was about 125 cm. long and with an internal diameter 

 of 4 cm. There was, therefore, no necessity to apply the 

 correction for diameter which is required for narrower tubes 

 (Kundt, Pogg. Ann. cxxvii. p. 497, 1866 ; cxxxv. p. 247, 

 1868 ; Kirchhoff, ibid, cxxxiv. p. 177, 1867 ; Thiesen, 

 Ann. Pliys. xxiv. p. 401, 1907). The tube had practically 

 the same internal diameter throughout, was free from 

 irregularities in the walls, and was straight. It was cleaned 

 with nitric acid, washed and dried. One end was sealed off 

 and blown as nearly hemispherical as possible. To the other 

 end a short tube with a ground connexion, J (fig. 1), was 



C<n=ii 



A 



D 



sealed, and the remaining part blown hemispherical as before. 

 The tube was then washed out with a mixture of concentrated 

 sulphuric acid and sodium dichromate, then with dilute 

 nitric acid, and finally several times with hot distilled water 

 quite free from grease. The water was then allowed to 

 drain out by inverting the tube. Complete cleaning is most 

 essential. 



The powder used was silica. This was prepared by pouring 

 water-glass diluted with its own volume of water into con- 

 centrated hydrochloric acid with constant stirring. The jelly 

 formed was then heated on a water-bath for some time, and 

 the acid decanted off. The residue was extracted and washed 

 several times with concentrated, then with dilute hydrochloric 

 acid, and finally with hot distilled water until the liquid was 



