Index of Refraction of Liquefied Gases. 357 



To these results I add the following remarks. 



1. The values are calculated from the indices determined with the 

 natrium flame, and not corrected for dispersion. LorenB observes 

 that the deduction of the index of refraction for undulations of 

 infinite length is not possible with the same exactitude as is attained 

 by direct observations with visible light, and prefers, therefore, to 

 apply the experimental results in the formula. 



2. As Lorenz has determined by experiment for each substance 

 in its fluid and gaseous condition the amount of dispersion, and this 

 remains nearly the same in both cases, he concludes that this justifies 

 the use made of the expression for undulations of definite length, 

 though it was deduced from those of infinite length. 



3. The recorded calculations point out that, though a great change 

 in specific gravity occurs when a substance is passing from one con- 

 dition into another, yet the relation between the refraction and the 

 density approaches closely to a constant value, the greatest difference 

 amounting to 5 per cent, with the acetate of ethyl. It also appears 

 that the expression established on theoretical grounds answers far 

 better to the experiments than the empirical one, as is evident from 

 the three latter columns in the tables. 



I was induced by these considerations to try how far my own 

 experiments would support these results, though less concordance is 

 to be expected, as the exactitude is already impaired at the third 

 decimal of the observed value. 



The next table contains my determinations put together with other 

 quantities belonging to the same substance and required for calcula- 

 tion by both expressions. The indices of refraction of the gases are 

 partly taken from the paper of Dulong* and others, occasionally from 

 more recent and accurate researches made by Ketteler, Lorenz, and 

 ^Croullebois. The densities of H 3 N,-C0 2 , S0 2 , N 2 in liquid condition 

 have been accurately determined by Andreef, that of liquid HC1 by 

 Ansdell.J As in Dulong's researches no special light is mentioned, 

 it must be assumed that daylight was used in determining the 

 refraction ; I therefore employed my own corresponding values, taken 

 with common light, for comparison, inasmuch as no recent experi- 

 ments on gases with natrium light have been published. 



From the results in the table, it is again evident that, though no 



* Dulong: "Kecherches sur les Pouvoirs Kefringents des Fluides filastiques,' 1 

 1825. Croullebois : " Annales de Chimie et de Physique," 1870, t. 20. 



t Andreef : " Annalen der Chimie u. Phannacie," 1859, p. 1. 



J Ansdell : " Proc. Koy. Soc.," vol. 30, p. 221. He applied the compression 

 apparatus of Cailletet, and I followed this very useful method with phosphoretted 

 hydrogen, sulphuretted hydrogen, and ethylene. The specific weights of the other 

 liquefied substances are taken from the " Physik. u. Chem. Tabelle" of Bornstein 

 u. Landolt. 



