1914] on The Coining of Age of the Vacuum Flask 255 



temperature exists. It was necessary that, as far as possible, the 

 bodies used should be subjected to this variable region in the same 

 manner, so that the amount of heat absorbed in transit should be 

 nearly the same. This value was determined in the following 

 manner. The warm portion of the calorimeter neck between the 

 cooling vessel above and the vacuum vessels below was cooled by 

 being surrounded with liquid air placed in a simple temporary fitting. 

 Observations with various kinds of bodies were then made. The 

 comparison of the reduced volumes now obtained with the values 

 given by the ordinary use of this particular form of the instrument 

 gives the correction factor. Many confirmations of the specific heats 

 were made with this addition to the instrument. In the latest form 

 of the calorimeter the neck is always surrounded with liquid nitrogen, 

 thus abolishing all heat correction. This improved calorimeter gives 

 results differing but slightly from the corrected values of the old 

 instrument. The value of the atomic heat of lead is determined 

 before and after any series of experiments as a check on the con- 

 stancy of the instrument. 



The values of the specific heats given will include any heat of 

 transformation of glassy or crystalline modifications or other com- 

 parable change produced by the cooling to 20° Abs. Another effect 

 is produced by some materials when used in the form of hydraulically 

 compressed blocks. Such as are porous exhibit in varying degrees 

 the phenomenon of heat evolution due to liquid hydrogen passing 

 into the capillary spaces, thereby rendering the observed specific heat 

 too great unless the proper correction is made. Any air occluded 

 during the preliminary cooling of the porous material to liquid air 

 temperature before being introduced to the hydrogen calorimeter is 

 also included. Some of this air would be replaced by hydrogen 

 through diffusion while in the hydrogen atmosphere in the^ central 

 tube of the cooling vessel of boiling nitrogen ; but the true remedy 

 is the preliminary cooling of such porous bodies in a hydrogen 

 atmosphere at the temperature of liquid air. That heat evolution 

 continued in many cases for some time after the dropping of the 

 material was shown by an increased rate of evolution of hydrogen 

 from the calorimeter. As stated above, this is normally less than 

 10 c.c. per minute. In some cases the introduction of porous 

 material increased this for some time to more than 30 c.c. per minute. 



The values set out in Table I for the mean atomic specific heats 

 of 58 elements at about 50° Abs. represent the results of some 200 

 calorimetric observations. When plotted in terms of their atomic 

 weights, they reveal definitely a periodic variation resembling 

 generally the well-known Lothar Meyer atomic volume curve for the 

 solid state. The relations between the two curves is shown in Fig. 7. 

 If experiments were similarly made between the boiling points of 

 hydrogen and helium then in all probabihty the atomic specific heats 

 would be all very small and nearly constant. 



