Jjidex of Refraction of Liquefied Gases. 361 



index of refraction and density* (experimentally determined), and the 

 atomic weight. It is obvious that by subtraction of the proper 

 experimental values we may obtain the mean refraction equivalent of 

 hydrogen, thus determined from observations on the liquid acids 

 themselves, and not in solution. We have for both expressions 





MX (-!)/& MX ( 



HC1-C1 ...... 10-9 - 9-6=1-3 ....... 6-9-6 =0 '9 



HBr-Br ...'.. 16-2 -15 -3=0 '9 ....... 10 "0- 8 79=1 -21 



HI-I . . 26-3-24-9 = 1-4. 15-5-14-3=1-2 



Mean value of H 1 '2 1 -10 



Calculated value from other 



substances 1 '3 1 -04 



The conclusion is that the concordance between the value deduced 

 from my experiments and that obtained from other observations is 

 tolerably satisfactory, f and the remark that the equivalent of 

 refraction of hydrogen in an inorganic combination, and especially in 

 an inorganic acid,J amounts to 3'5, is not applicable to liquefied 

 hydrochloric acid, nor hydrobromic and hydriodic acid. They were 

 till now only examined in their solutions in water, and it has already 

 been pointed out by Landolt and others that the dissolving medium 

 does not exert the same influence on the index of refraction as on 

 the density ; my experiments being free from this influence may be 

 deemed appropriate to fix the value of the atomic refraction of 

 hydrogen in these compounds. 



* I had to determine the density of liquid hydrobromic and hydriodic acid, 

 hitherto unknown. I could not well apply the method of the compression apparatus, 

 as the mercury is somewhat attacked by the liquefied gases. I therefore employed 

 the Faraday tubes, with glass cell, described before, and provided at the end with a 

 calibrated capillary tube. The tube with its contents and the liquefied gas was 

 weighed ; then, by unscrewing the glass cell a little, a certain quantity of the liquid 

 was allowed to escape. The cell was closed and the whole tube weighed again. The 

 diminution in weight observed gave that of the escaped liquefied gas, and its volume 

 was before noted in the capillary part of the tube. I have found the specific weight 

 of liquid HBr = T63 at 10, that of liquid HI = 2'27 at 12. 



f The difference between calculation and experiment in this case may perhaps be 

 accounted for by the difference existing between the values communicated by various 

 observers for the same substance. In the table the ref r. equiv. of iodine given by 

 Landolt as 24'87, is used ; if I had admitted the value given by Professor Gladstone 

 as 24'5, the refr. equiv. of hydrogen would have amounted to 1*3, according exactly 

 with other observations. 



J Professor Gladstone, loc. cit. I have shown previously that also from an 

 electro-chemical point of view these liquids differ essentially from their aqueous 

 solutions. 



Bruhl, loc. cit., p. 222. 



