250 The Coming of Age of the Vacuum Flask [Jan. 23, 



30 observations. The greatest variations from this mean value were 

 0'0247 and 0*0233, but the majority of the values varied to a much 

 less extent. This is equivalent to an atomic specific heat of 4*965. 

 It may be mentioned that a computation from Xernst and Linde- 

 mann's* real specific heats of lead within the same range of tempera- 

 ture gives the mean value 5 1<S. 



In the observations with the liquid air calorimeter the specific 

 heats were calculated in each case by direct comparison with lead 

 observed at the same time, as explained in the earlier papers. This 

 is most convenient because liquid air varies in composition on 

 standing, and therefore in the volume evaporated by unit amount 

 of heat. 



Liquid Hydrogen Calorbieter. 



The liquid hydrogen calorimeter is a glass cylindrical bull) vacuum 

 vessel A (Fig. 6) of 50 c.c. capacity, silvered, with J cm. slit. The 

 inner diameter is 3 cm. On to the neck, contracted to about 

 1*7 cm., is sealed a glass tube B of equal diameter and 3(» cm. 

 long. This projects about 8 cm. through the brass coned fitting 

 cap F of an ordinary slit silvered vacuum vessel in which it is sup- 

 ported. A side delivery tube, 1 cm. wide, provided with a stopcock 

 D of 8 mm. bore, is sealed near the top of B. A short length of 

 rubber tubing on the neck of F makes a gas-tight joint with B. To 

 minimise splashing, and to reduce tlie impact of the fallins: pieces, 

 a thin strip of german silver or lead E, bent out near the top into 

 a shoulder about 1 cm. square, stands centrally in the calorimeter A. 

 The strip is cut from a thin tube of about the same diameter as the 

 calorimeter neck. A short length of the tube is left above the 

 shoulder, and supports the strip by fitting loosely into the neck 

 of A. The shoulder is arranged just above the level of the liquid 

 hydrogen in A, which is at least three-quarters full. Some such 

 device is essential in the use of this form of the liquid hydrogen 

 calorimeter. 



The calorimeter in its turn is immersed in liquid hydrogen in the 

 supporting vacuum vessel C, the neck of the calorimeter being 8 to 

 10 cm. below the liquid hydrogen surface. This vacuum vessel C is 

 only slightly wider than the lower part of A, and is provided with a 

 coned cap F, whereby it is also supported and completely immersed 

 in a wider vacuum vessel G containing exhausted liquid air. G is 

 also fitted with a brass coned cover, fitting vacuum-tight to the cap 

 F on C. Both caps are pierced by two thin tubes, one for fitting on 

 to the filling syphons, the other, bent at right angles, serves for 

 connecting to the exhaust in the case of the liquid air vessel, and in 

 the case of the liquid hydrogen vessel to the stopcock leading the 

 evaporating hydrogen through the upper part of the apparatus. 



* Sitzungsber. d. Berl. Akad., 1911, p. 494. 



