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XXIX. The Spontaneous Change of Oxygen into Ozone 

 and a Remarkable Type of Dissociation. By William 

 Sutherland*. 



IX 1886, in connexion with a physiological inquiry, Bohr 

 (Wied. Ann. xxvii.) carne across a singular discontinuity 

 in the behaviour of rarefied oxygen, as well as a very pro- 

 nounced departure from Boyle's law ; between 14° and li'4 G. 

 the discontinuity occurs at a pressure of about *7 millim. 

 of mercury, above which Boyle's law is replaced by 

 (jt?4- '109)6 = ^, which was experimentally tested up to 

 15 millim., and below *7 millim. the pressure relation is 

 (p -\-'0 7) B = A/, where k r = l'OAbk, this being experimentally 

 verified down to *1 millim. ; thus the discontinuity consists 

 in a change of volume from #/'809 to k' I'll at a constant 

 pressure of '1 millim. It is to be remembered that Bohr's 

 pressures were all directly read with a cathetometer from the 

 difference of level of mercury in two wide tubes, so that there 

 is no question of the departure from Boyle's law being only 

 an apparent one, due to a fallacious step in a train of reason- 

 ing. At a pressure of *07 millim. the departure from Boyle's 

 law is no trifle, for a reliable M'Leod gauge worked on the 

 assumption of Boyle's law would make a true pressure of 

 07 millim. appear to be twice as large. 



We have already seen in u Thermal Transpiration and 

 Radiometer Motion " f that in Crookes's study of radiometer 

 repulsion for different gases with his torsion radiometer, 

 oxygen at a pressure about '16 millim. or 1000/10 6 atmo 

 exhibits a remarkable difference from other gases, showing a 

 deflecting force 12 times as great as that of X 2 or C0 2 , and 

 6 times as great as that of CO, and the anomaly continues 

 till a pressure of about 300/10 6 to 200/10 6 atmo in Crookes's 

 list of pressures. Here are the complete results for the 

 anomalous region, with the addition of what the deflecting 

 force ought to be according to (26) of " Thermal Transpira- 

 tion and Radiometer Motion " with the values of c' ', A", and 

 B w there given for oxygen, as derived from the region of 

 lower pressures, where all is apparently regular; the so- 

 called pressures are given in terms of 1/10 6 atmo as unit. 



p 1000 803 658 623 613 360 297 190 



10 4 log. dec... 1102 1093 1088 1086 1085 1070 1058 103S 



Defl. force 12 12 13 13 13 13 14 20 



Defl. force cal. 42 5 2 6*3 6-6 67 111 13-3 19*8 



* Communicated bv the Author, 

 t Phil. Mag. vol. xlii. 



Phil. Mag. 8. 5. Vol. 43. No. 262. March .1897. R 



