376 Prof. Partington and Mr. Cant on the Specific Heats 

 From (1) we obtain, for two ideal gases, 



<-*'i0- •■';•■ V -..'••■• .5 



where X is the wave-length of sound in the gas and d the 

 ideal density. 



From c p /c v and Cp — C,, we can calculate Cp and C B 

 separately. 



Ammonia. — The following table gives the results with 

 ammonia. 



Table II. 



Number of 

 Experiment. 



^NH 3 cm. 



2 3 



X . 



— air cm. 



1 K '- 



1 



2 



3 



10286 

 10340 

 10-334 

 10-316 

 10-326 



8-261 



8-281 

 8-277 

 8-254 

 8-295 



1-277 



1-284 

 1-284 

 1-287 

 1-276 



4 



5... 



Mean k' = 1-285. Mean temperature 14°'5 0. 



p for NH 3 =115 atm. ; T c =403° abs. (Kaye and Laby's 

 Tables.) Thus, from (4) </> for NH 3 under the conditions 

 of experiment is 1'0j85. From (6) we find G p -C v = 2'065 

 g. cal. The values of tc 2 given in all the tables in this 

 paper are calculated by (7) with k\ for air taken as 1*403 

 (Partington, PJiys. Zeit. xiv. p. 969, 1913), and d 2 /d i is the 

 ratio of the molecular weights (air = 28*98). Thus, for 

 ammonia (d 2 /d 1 = 17*03/28*98), 



K = c P lc v = l'3Q8 ; C, = 6*70 g. cal. ; 



Cp = 8*77 g. cal. (all at 14°*5 at 1 atm.). 



Keutel (loc. cit.) carried out a series of experiments similar 

 to those described above, but he filled his tubes directly 

 from the supply cylinder and corrected his results by Van 

 der Waals's equation. He gives 1*302 and 1*304 as the 

 uncorrected and corrected results, respectively, for c v \c v at 

 20° at 1 atm. Scholer {Ann. Phys. [iv.] xlv. p. 913, 1914), 

 also using Behn and Geiger's modification of Kundt's method, 

 obtained the values 1*287 (uncorrected) and 1*305 (corrected) 

 at 20° and 1 atm. The " corrected " value was obtained 

 merely by using the experimental ratio d 2 /di in (7) instead 



