EXPANSION OF GASES. 



43 



that A was left in communication with the external air, and it was kept 

 at the boiling-point for some time. The junction j was then disconnected 

 and the end of the tube was sealed by a blowpipe flame, the bulb thus being 



J 



J! 



FIG. 34. Regnault's Apparatus for Expansion of Gas at Constant Pressure 

 (Rudberg's method). Bulb filled with gas at 100 C. and sealed. 



filled with dry air at the atmospheric pressure, and at the temperature 



of the boiling-point. It was then arranged as in Fig. 35, being inverted 



with the end of the tube under mercury, the bulb being surrounded with 



melting ice. The end of the tube was broken off, and the mercury rose 



into the bulb through the contraction of the 



air. After some time the end of the tube was 



closed by a small piece of wax, which could be 



pressed up against it by the arm w. The 



height of the mercury in the bulb above that 



in the lower vessel was then determined, and 



from this could be found the pressure to which 



the air was subjected. The bulb was taken 



away and weighed, first when thus partially 



filled with the mercury which had risen into it, 



and afterwards when quite filled, and so it was 



easy to determine what fraction of the volume 



the air occupied at 0. By correcting for the 



reduced pressure, the fraction of the volume 



which it would have occupied at the atmospheric 



pressure was calculated. The air occupying this FIG. 35. Regnault's Expan- 



volume at expanded at 100 to fill the whole s n of Gas at Constant 



, n /. ic C i -i. i-u \, it- Pressure (Rudberg s 



bulb (itself of larger capacity through the ex- Method). Bulb opened 



pansion of the glass), and so the expansion under mercury, 

 could be calculated. 



Regnault also devised another method represented in Fig. 36. The 

 bulb A communicated by a capillary tube with the manometer MM', 

 placed in a constant-temperature water-bath with glass sides. R was a 



