as to the Constitution of Chlorine. 



39 



stance may perhaps be wrong by one in some of the simpler 

 bodies, and by rather larger numbers in some of the more 

 complex ; but the general character of the Tables is probably 

 beyond the reach of any such changes. An error e. g. of 6 

 per cent, in the specific heat at constant pressure of the tetra- 

 chlorides would only reduce the number of their degrees of 

 freedom by one. Much greater alterations would be intro- 

 duced by taking the specific heats at other temperatures than 

 those at which they were determined by Regnault. Chloro- 

 form is the only compound of chlorine of which the law of the 

 variation of the specific heat with the temperature was studied 

 by Wiedemann ; and using his results, I find that at 0° C. the 

 number of degrees of freedom of this substance would be one 

 less instead of two greater than 15. 



In spite, however, of the uncertainty thus introduced, the 

 comparison of the two Tables is sufficiently suggestive to in- 

 duce me to lay them before the Physical Society. The fact 

 that the application of the theory of gases to the specific heats 

 of a large number of substances, determined as far as might 

 be under similar circumstances, leads to the alternatives that 

 the atoms of which a molecule of free chlorine is composed are 

 either less strongly united or are more numerous than in the 

 case of other elements, is not unimportant. 



It remains to add that the ratios of the specific heats of bro- 

 mine and of the only one of its compounds which has been 

 studied agree with those of chlorine and the corresponding 

 chlorine compound. 



Table III. 



I. 



II. 



III. 



IV. 



V. 





Cv' 



m-\-e. 



3n. 





Br 2 



C 2 H s Br ... 



1-302 

 1-114 



7 

 18 



6 

 24 



18 

 30 



Note. — Since the above was written, the conclusions at first 

 drawn from Prof. V. Meyer's research have been questioned 

 (Chem. News, Nov. 21, 1879, p. 244) on the ground that experi- 

 ments made by Seelheim, of Utrecht, indicate the possibility of 

 the formation of a volatile chloride of platinumat high tempe- 

 ratures. However this may be, the cause of the anomalous 

 specific heats of chlorine and its compounds remains to be ex- 

 plained ; and the above statement of the alternative supposi- 

 tions to which the theory discussed leads may not be uninter- 

 esting, even if it should be proved that one of them lacks the 

 support which, at the time of writing, Prof. V. Meyer's research 

 was supposed to afford it. 



