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XXXVIII. The Specific Heats of Ammonia, Sulphur dioxide, 

 and Carbon dioxide. By Prof. J. R. Paktington and 

 Mr. H. J. Cant *. 



IN recent years the theory of specific heats has been 

 prominent, but the subject is still very incomplete. In 

 the case of solids, the work of Planck, Einstein, Nernst, 

 Lindemann, and Debye, based on the Quantum Theory*, has 

 resulted in notable advances. In the case of gases, however, 

 the treatment has principally been based on the theory of 

 Equipartition of Energy, which is now known to be of very 

 restricted validity, and fails altogether in the case of solid 

 bodies at low temperatures. The application of the Quantum 

 Theory to gases has been most incomplete, and the results 

 are far from satisfactory. 



The determinations described in the present communication 

 were carried out with the object of obtaining reasonably 

 accurate data which might be used in theoretical discussion : 

 the paper deals only with the experimental results, and does 

 not enter into questions of theory, which are deferred until 

 more data are available. 



The method employed was that of Kundt, as modified by 

 U. Behn and H. (leiger, the method of filling the gas-tubes 

 being that described by Partington (Phys. Zeit. xv. p. 601, 

 1914). A tube of suitable dimensions is filled with the 

 gas under investigation, and contains also a small amount of 

 some light powder unaffected by the gas. The tube is sealed 

 at both ends, which are as far as possible symmetrical, and 

 is clamped in the middle. When the tube is set in vibration 

 by stroking, it is usually found that the dust figures are very 

 irregular, if any appear at all. Such a tube is chosen that 

 its mass is a little too small to vibrate in resonance with the 

 contained gas. To produce resonance, circular rings cut 

 from thin sheet-lead are cemented on the two ends of the 

 tube symmetrically. The hole in the middle of each ring is 

 to admit the projection at each end, or at one end, of the 

 tube where it was sealed off. 



One end of this tube is then brought inside another, slightly 

 wider, tube, open at both ends. This tube is fitted with a 

 cork piston and contains a small quantity of the same powder 

 as the sealed tube. By varying the position of the piston 

 the position for resonance in the air inside the open tube is 

 found, and when the gas tube is set in vibration sharp dust 

 fiVures are formed in both tubes. The wave-lengths of 



* Communicated by the Authors. 



Phil. Mag. S. 6. Vol. 43. No. 254. Feb. 1922. 2 B 



