Section III, 1922 [63] Trans. R.S.C 



The Varifition of the Refractive Index of Oxygen with Pressure and 

 the Absorption of Light by Oxygen at High Pressures. 



By Miss H. I. Eadie, M.A. and John Satterly, F. R.S.C. 



Communicated by Prof. J. C. McLennan, F. R.S.C. 



(Read May Meeting, 1922) 



I. The Refractive Index. 



The determination of the refractive index of oxygen has been 

 carried out at moderately high pressures in order to test the relation 

 between the refractive index and the density. 

 The three statements of this relation are 



(1) Gladstone and Dale, («— l)/p = a constant 



(2) Drude, (n2—l)/p = a constant 



(3) LorenzandLorentz, (n^— l)/(«- + 2)p = a constant 



A Jamin interferometer was used for the work. The instrument — ■ 

 made by Hilger of London — 'consists of the'usual two parallel glass 

 blocks of equal thickness, silvered on the back surface and mounted 

 on a heavy metal base. The source of light was an Ediswan Pointo- 

 lite lamp P (Fig. 2). The light, made parallel by a lens, was reflected 

 from the mirrors /,/ in turn and finally fell upon the slit of a Hilger 

 constant deviation spectroscope.* By setting the drum of the spec- 

 troscope at any particular wave-length the fringes obtained in the 

 field of the eyepiece or rather those at the centre of the field were 

 produced by light of that particular wave length. As usually employed 

 in gas refractometry the Jamin instrument is provided with two 

 glass tubes having plane parallel glass ends. The two beams from the 

 first mirror traverse these tubes. When the tubes are filled with 

 the same gas at the same temperature and pressure there is no 

 optical path difference. If, now, the gas in one tube is gradually 

 compressed or rarefied a path difference is set up and the fringes 

 move across the field of view. 



If /= number of fringes passing cross hair of telescope when the 

 pressure in the gas drops back from P mms. to 760 mms., X = wave- 

 length of the light used (in the gas at normal pressure), Mp,« = the 

 refractive indices at pressures P and 760 mms. respectively, pp,p 



^This was calibrated from time to time with a mercury lampl 



