I6 MR n.lVK PBTHBBMSON AND M AM-.: CUTIIHERTSON ON THE 



thw , M the value for the*** n.ercury line. The variations of these experiments 



t.^ ADBU1U nif, > , j ] 



from seven experiment* with the largest charge of water, the number of bands read 

 being about 380 for X = 5461 :- 



TABLE VIII. Dispersion of Steam. 



Using the SKI.KMKYEK equation the refractivity can be expressed by 



, ,s_D_ 2-62707 x 10 a; 

 'd 76 ~ 10697 xlO 27 -?! 2 ' 



The numljers calculated from this expression are shown in the third column and 

 the differences between column 3 and 2 are given in column 4. 



OZONE. 



/'/,// I/.N- II'.. rk. No previous work on the refractivity of ozone is recorded in the 

 usual books of reference. The difficulties are considerable. It is impossible to 

 prepare ozone even approximately pure, and if it were possible it would be inadvisable 

 to do so, since the decomposition of the molecules during the time necessary to 

 measure the refraction and dispersion would introduce fruitful sources of error. 



fVponhtre. Of the two best methods of preparing the gas, electrolysis of a 

 solution <>f sulphuric acid has produced the highest percentages of ozone, FISCHER 

 and MASSENEZ* having obtained over 28 per cent, by weight. But the objections to 

 this method seemed to us to outweigh its advantages. It was necessary that the gas 

 used should be absolutely pure oxygen, for the smallest trace of moisture, air or 

 hydrogen would introduce large errors; and in the electrolytic process the gas is 



v f O 



produced wet and is mixed with air in the connections. For these reasons the method 

 selected was that of ozonising by means of the silent discharge in a vessel of the type 



* ' Zeit. fur Anorg. Chemic,' vol. 52, p. 229, 1907. 



