208 Professors Li vein v and Dewar on the 



& 



apparatus to pieces, comminuting the tube to fine powder. 

 This instability of ozone, equally at very low and at high 

 temperatures, is a significant fact in regard to the form of 

 chemical energy. It seems probable that it is connected 

 with the great absorbent power of ozone. The radiant energy 

 absorbed must give rise to molecular movements which may, 

 we conceive, set up disintegration. 



The determination of the refractive index of liquid oxygen, 

 at its boiling-point of —182° C, presented more difficulty than 

 would have been anticipated. The necessity for enclosing 

 the vessel containing the liquid in an outer case to prevent 

 the deposit of a layer of hoar-frost which would scatter all 

 the rays falling on it, rendered manipulation difficult ; and 

 hollow prisms with cemented sides cracked with the extreme 

 cold. It was only after repeated attempts, involving the 

 expenditure of a whole litre of liquid oxygen on each ex- 

 periment, that we succeeded in getting an approximate measure 

 of the refractive index for the D line of sodium. The mean 

 of several observations gave the minimum deviation with a 

 prism of 59° 15' to be 15° 11' 30", and thence ^ = 1*2236. 

 The density of liquid oxygen at its boiling-point of —182° C. is 



1*124, and this gives for the refraction-constant, =1*989, 



and for the refraction-equivalent 3*182. This corresponds 

 closely with the refraction-equivalent deduced by Landolt from 

 the refractive indices of a number of organic compounds. 

 Also it differs little from the refraction -equivalent for gaseous 

 oxygen, which is 3*0316. This is quite consistent with the 

 supposition that the molecules of oxygen in the liquid state 

 are the same as in the gaseous. 



a 2 — 1 

 If we take the formula 7-^ — ^t-i for the refraction-constant 



(fj? + 2)d 



we find the value of it for liquid oxygen to be *1265, and the 

 corresponding refraction-equivalent 2-024. These are exactly 

 the means of the values found by Mascart and Lorenz for 

 gaseous oxygen. The inherent difficulties of manipulation, 

 and the fact that the sides of the hollow prism invariably 

 became coated with a solid deposit, perhaps solid nitrogen, 

 which obscured the image of the source of light, have hitherto 

 prevented our determining the refractive indices for rays 

 other than D*. 



* This will be prosecuted further, however. The refractive index of 

 oxygen has an important bearing on the electro-magnetic theory of light, 

 considering that we are dealing with a magnetic liquid. The polarizing 



