REFRACTION AND IMsl'KKSlON OF THE HALOGENS, HALOGEN ACIDS, ETC. 19 



Second method. To check these results a second set of experiments was made, in 

 which the quantity of ozone was estimated by chemical testa This method was 

 found to give more concordant figures. 



TAISI.I: X. Refractivity of pure Ozone. (Second Method.) 



The results obtained by the two methods are tolerably concordant, and would be 

 even better if the third experiment were omitted. 



Their mean is 5207, but having regard to the smallness of the proportion of ozone 

 present it would be unsafe to rely on this number beyond the second significant 

 figure, and we therefore conclude that the refractive index of pure ozone for the 

 mercury green line is 



/x = 1'00052. 



Comparison with the Refractive Index of Oxygen. It will be observed that this 

 result is remarkable. 



The refractivity of oxygen is '0002717, and if the third atom of oxygen on joining 

 the molecule had the same refractive effect as in the normal gas we should expect a 

 refractivity ( M -l) 10 7 of $ x 2717 = 407 '5. 



The experimental value 520 is very largely in excess of this, and indicates the 

 existence of interesting peculiarities in the molecule which may probably be ascribed 

 to the linkage. 



Dispersion of Ozone. Nine experiments were made on the dispersion of mixtures 

 of ozone and oxygen. In each of these the refractive index of the mixture for the 

 green mercury line was separately determined, and the other seven refractivities 

 were calculated 'with reference to it from the observations as previously described. 



The first experiment, being a trial, is omitted, and the refractivity of ozone 

 calculated from the remaining eight as follows : 



D 2 



