Index of Refraction of Liquefied Gases. 



349 



it may be concluded that when some precautions are taken the micro- 

 scopical method may give reliable results. Of course, a high magni- 

 fying power was used in the fore-mentioned experiment that could 

 not be applied when dealing with liquefied gases, still good results 

 are possible even with a magnifying power of 30, as is evident from 

 the following table containing observations on sulphuric ether and 

 water taken in cells of different heights. 



The determinations from the correct values are within the limits of 

 the probable error, and I must observe that even with very accurate 

 methods, attaining four decimals, the results given by different 

 experimenters vary in the third decimal, for instance, with sulphuric 

 ether at 15, Gladstone and Dale found the index (D line) T3566 ; 

 Kundt, however, T3594. 



IV. Experiments on the Refraction of Liqtiefied Gases. 



I will now proceed to give the results of the experiments bearing 

 on several liquefied gases, and made as described above. Therefore 

 I think it sufficient, after the foregoing explanations, to give for each 

 gas the final results for the values of D, d, and n, these having the 

 same signification as in the former chapter. Yet I must add that 

 during a space of four years I repeated at different times the deter- 

 minations for each gas with different vessels ; in this way the number 

 of single observations has amounted to some thousands, consisting of 

 series of six or eight terms. I commonly employed as source of 

 light the flame of a Bunsen gas-burner, containing a piece of woven 

 asbestos, moistened with a solution of natrium chloride, and pro- 

 ducing an excellent monochromatic light. Sometimes I also experi- 

 mented with ordinary daylight ; this was necessitated by some calcu- 

 lations, as will be seen in the next chapter. 



1. Sulphurous Acid (S0 2 ). 



The gas was prepared in the usual way, and liquefied in a tube con- 

 nected with a parallel-sided glass cell by means of a freetiuer mixture. 



2~A 2 



