5 tO M. V. Regnault on an Air-Thermometer. 



exist on the inner side of the tube A B will be reduced to the 

 metallic state. 



The stopcock R is then turned into the position 2 (fig. 8), the 

 hydrogen-apparatus is detached from the tubulurc /, and the 

 tubulure e is connected with an apparatus which disengages, 

 when convenient, dry air with a velocity which can be regulated. 

 This apparatus, represented by fig. 9, consists of a tubulated 

 flask V, into which water passes from a higher reservoir X, 

 through a leaden tube a b, provided with a stopcock r, by which 

 the flow of water can be regulated. The air of the flask V traverses 

 a tube c d, filled with pumice saturated with strong sulphuric 

 acid. When the stopcock r f is closed, the air in the flask V is 

 under a higher pressure than that of the atmosphere, for it sup- 

 ports in addition the pressure of the column of water a b. 



Thus, when the temperature of the furnace is to be determined, 

 the tube A B is filled with hydrogen under the pressure of the 

 atmosphere H , and at the unknown temperature x. Further, the 

 copper tube C, filled with oxide of copper, is heated to redness by 

 a row of gas-burners ; lastly, its second tubulure, i, communicates 

 with a U-tube, filled with pumice saturated with sulphuric acid, 

 and which has been previously weighed. The stopcock R is in 

 the position 2 (fig. 8), and the stopcock R' in the position 3 

 (fig. 8). The stopcock R' is opened for a moment to expel the 

 hydrogen of the tubulure ef; R/ is then placed in the position 1 

 (fig. 8), finally in the position 3 (fig. 8). The stopcock r 1 of the 

 air-vessel is then carefully opened (fig. 9) ; dry air passes 

 slowly into the large tube A B ; expels from it the hydrogen, 

 which partially burns, and drives the remainder over the hot 

 oxide of copper, where it burns completely; the water arising 

 from this combustion condenses in the sulphuric acid tube S. 

 The current of air is continued until the hydrogen and aqueous 

 vapour are completely expelled from the tube AB. The 

 reduced oxide of copper reoxidizes in this current of air. 



Let 



V be the capacity of the apparatus at 0° in cubic centimetres. 



8 the density of hydrogen as compared with air. 



a the coefficient of expansion of this gas. 



k the coefficient of cubical expansion of the metal of which 

 the tube A B is made. 



P the weight of water collected in the tube S. 

 We shall have 



V l±*£ .8. 0-0012932 . * =P 1^50 

 l+ax 760 112-50 



In a preliminary experiment, made in the same apparatus 

 before the tube A B had been arranged in the furnace, A B was 



