of Molecular Refraction and Dispersion. 209 



such as the xanthates, sulphur has at least the value of 160 ; 

 but in the large majority of cases it has a distinctly lower 

 value. In its oxygen compounds it is known to be far less 

 refractive and dispersive. 



IV. Liquefied Oxygen, Nitrous Oxide, and Ethylene. 



In the recent paper of Professors Liveing and Dewar (Phil. 

 Mag., Aug. 1892) they give determinations of the specific 

 refraction of liquefied oxygen, nitrous oxide, and ethylene. 

 It is, of course, possible to compare these interesting results 

 with what theory would have led us to expect. The authors 

 have themselves done so in the case of liquid oxygen at its 

 boiling-point of —182° C. They remark that the refraction- 

 equivalent, 3*182, which they found, differs but little from 

 that deduced from gaseous oxygen at the ordinary tempera- 

 ture, viz. 3*0316, and " corresponds closely with the refrac- 

 tion-equivalent deduced by Landolt from the refractive indices 

 of a number of organic compounds," which was 3*0. It 

 actually comes between the two values, 2*8 and 3*4, which 

 were assigned by Briihl to oxygen in its different states of 

 combination with carbon, and to which an intermediate value 

 has since been added. 



Liveing and Dewar were able to determine the refraction 

 of liquefied nitrous oxide for six different wave-lengths, the 

 extremes being the red ray of lithium and G. These gave 



for 0'2595 and 0*2691 respectively, and for the mole- 



cular refraction of the red ray 11*418, and of G 11*840. The 

 molecular dispersion between G and the lithium-line is there- 

 fore 0*422, which would indicate about 0*63 between H and 

 A. Now it is difficult to say what the rational composition 

 of nitrous oxide is, and therefore what its theoretical refraction 

 and dispersion should be. Nitrogen in ammonia and its con- 

 geners is reckoned at 5*1, in nitriles at 4*1 ; oxygen double- 

 bonded is reckoned at 3*4, with two separate bonds at 2'8. 

 We therefore, according to our theoretical views, might reckon 

 nitrous oxide at 13*6, 13*0, 11*6, or 11*0. The probability is 

 therefore clearly in favour of the lower figure for nitrogen. 

 As the dispersion- equivalent of nitrogen in ammonia is as 

 high as 0*38, this would also seem to exclude the idea of the 

 nitrogen in nitrous oxide being in the same condition as in 

 ammonia. This will probably be considered the most likely 

 alternative also on chemical grounds. 



On calculating Messrs. Liveing and Dewar's numbers for 

 liquid ethylene, we obtain the molecular refraction of 17*2 for 



