270-273] Ratio of Specific Heats 225 



Thus the introduction of the series of chlorine atoms increases ?? very 

 perceptibly at every step. 



A similar result was obtained by Strecker*, who shewed that hydro- 

 chloric, hydrobromic, hydriodic acids all have approximately the same values 

 as hydrogen, namely 



7=1-4, 71 + 3 = 5, 



while for chlorine, bromine and iodine, the values are approximately 

 Chlorine 7 = 1-.333 n + 3 = 6 



Bromine, Iodine 7 = 1*293 n + 3 = 6*8. 



Similarly for the iodides of bromine and chlorine, 



Bromine iodide 7=1*33 % + 3 = 6 

 Chlorine iodide 7=1*317 n + 3=6*3. 



From these figures it appears that one halogen can be put in the place 

 of hydrogen without producing any difference in the values of 7 and n, but 

 that the substitution of the second halogen atom causes a marked increase 

 in n. Capstick*f* finds a similar phenomenon in the case of the paraffin 

 derivatives. In general the second chlorine atom introduced into the mole- 

 cule causes a large change, although the first may or may not do so. 



These facts will probably shew that the problem of determining a 

 relation between the value of n and the structure of the molecule is one of 

 extreme complexity, and moreover that it is a problem for the chemist rather 

 than for the mathematician. 



Non-integral values for n. 



273. A question which is still standing unanswered, is that of why the 

 values found for n + 3 are not exactly integral. Now in deducing the result 

 that this value ought to be integral, we have throughout supposed the gas 

 to consist of exactly similar molecules, whereas it is known that gases may 

 be partially in a state of dissociation or molecular aggregation. A gas 

 which is partially dissociated may be regarded as a mixture of the non- 

 dissociated gas, and another gas of simpler molecular structure. The 

 observed value for 7 will in this case not be one of the series of values 

 given by the simple theory, but will be intermediate between the values 

 appropriate for the component gases, so that the value of n deduced will not 

 be integral. The case of molecular aggregation is similar. Obviously dis- 

 sociation, being a tendency towards a simpler structure of molecule, tends 

 to raise the value of 7, whereas aggregation, being a tendency towards a 

 more complex structure, tends to decrease the value of 7. S 



* Wied. Ann. xm. p. 20; xvn. p. 85. 

 t I. c. ante. 

 J. 15 



