210 Mr. W. Sutherland on the Spontaneous 



As we have seen, at all the pressures given we have to 

 do at a temperature of 12° with mixtures of 2 and 3 , which 

 on being raised to 132° will have the whole or part of the 

 ozone dissociated into oxygen, and will therefore give a 

 larger coefficient of expansion than belongs to a pure gas. 

 In fact, if there is complete dissociation of the 3 at the 

 higher temperature, the number of molecules is increased 

 in the proportion of p + x to p, so that the mean coefficient 

 of expansion is increased to 1/273(1 -\-oijp) + a!/120p ; thus 

 with a' = *055 the reciprocal of the coefficient of expansion 

 becomes 263 at a pressure of 5 millim. and 231 at 1 millim., 

 numbers which are in close agreement with those of experi- 

 ment. At the two lowest pressures we ought to have to do 

 with pure ozone at the lower temperature, and if it is 

 entirely dissociated at the higher temperature the coefficient 

 of expansion will be 3/273 x 2 + 1/240, and its reciprocal 104 

 in place of about 240 as found by experiment ; accordingly 

 it appears that at the lowest pressures the ozone probably is 

 only partially dissociated at 132° C. Thus, although we 

 cannot draw definite quantitative results from these experi- 

 ments on the expansion of oxygen, we have ample qualitative 

 evidence that dissociation accompanies the expansion of what 

 has hitherto been considered to be pure rarefied oxygen, but 

 which is either a mixture of oxygen or ozone, or, at a low 

 enough pressure, pure ozone. 



In their experiments with oxygen Baly and Ramsay had 

 an extraordinary experience which will be traced to disso- 

 ciation. They had two M'Leod gauges in connexion with a 

 supply of oxygen whose pressure had been reduced to *75 

 millim., which is in the region of Bohr's discontinuity ; on 

 raising the mercury so as to shut off communication between 

 the two gauges, and then compressing each of the equal 

 volumes thus isolated at the same pressure into the fine 

 graduated tubes of the gauges where both pressure and 

 volume could be measured, they found that the mean value 

 of pB in the one gauge was 8*8 times as large as in the other, 

 whereas the two were expected to be equal ; it was only after 

 putting the gauges frequently in communication with one 

 another during 78 hours that the values of pB became equal. 

 The total volume of each gauge was about 90 cub. centim., so 

 that the original value of pB in both gauges was about 

 67*5, a rough estimate on account of the uncertainty in 

 measuring p near the discontinuous region ; but after com- 

 pression into the volume-tubes the value of pB in the one 

 was 53*1 and in the other 6*04, so that practically the whole 

 of the remarkable disturbance was confined to the one gauge. 



