[eadie-satterly] refractive INDEX OF OXYGEN 69 



. . 731 



Column 4 is obtained by multiplying column 3 by — • 



Column 5 is obtained by adding 75 cc. to column 4. 



Column 6 is an approximate value of the pressure obtained by dividing Column 

 5 by 75. 



Column 7 is obtained from Column 5 by multiplying the numbers in Column 5 

 by the density of oxygen at 21° and 750 mm. to get the total mass of oxygen 

 and then dividing by the volume, 75 cc. to get the density in gm. per cc. 



Column 8 is obtaiaed from the optical equation above. 



Column 9 gives the value of {n — \)/ p. It is seen to be practically constant thus 

 verifying the law of Gladstone and Dale for oxygen up to a pressure of nearly 

 40 atmospheres. The mean value of the constant is .192. 



Previous Work of a Similar Character. 



P. Phillips (Proc. Roy. Soc, Vol. 97) gives an account of work 

 done by him to find the relationship between the refractivity and 

 density of carbon dioxide. He used a Fabry and Perot étalon placed 

 within a strong metal chamber with glass windows. In order to work 

 over a large range of density he kept the temperature just above 

 the critical temperature cf carbon dioxide. Proceeding in much the 

 same way as described above he measured the continuous change of 

 refractivity from a density of .73 gm/cc. downwards. His results 

 for X = 5461 A.U. conform to the law 



^^—^ p = 6.581 + .1130p2 

 w2 + l 



This for small values of p is in agreement with Lorenz and Lorentz's 



expression. 



C. and M. Cuthbertson (Proc. Roy. Soc, Vol. 83) used a Jamin 



interferometer and worked between pressures of and 760 mm, 



n— 1 



From their data the value of for X = 5210 A.U. is found to be 



P 

 0.190. 



Rentschler (Astrophysical Journal, Vol. 28, 1908) used a Fabry 

 and Perot interferometer and pressures less than atmospheric. From 

 his data the value of (w— 1) p calculated for X = 5210 A.U. is 0.191. 



It will be seen that our value of {n — \)/p is in close agreement 

 with those of Cuthbertson and Rentschler and we have shown that 

 it remains constant up to a pressure of at least 40 atmospheres. 



Future Work 



To carry out work at higher pressures a double tube made by 

 boring two |" holes through a steel rod 10" long and .2" diam. will be 

 used. Great trouble was experienced in getting the windows at the 



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