On the Index of Refraction of Liquefied Gases. 339 



when large vessels of complicated form, like those used by me, have 

 to be put together and exhausted. All photographs were taken by 

 him. I have also to acknowledge valuable assistance from Mr. Moss, 

 a student at the Owens College. 



" On the Experimental Determination of the Index of Refrac- 

 tion of Liquefied Gases." By Dr. L. BLEEKRODE. Com- 

 municated by Dr. GLADSTONE, F.R.S. Received and read 

 June 19, 1884. 



I. Preliminary Remarks. 



On a previous occasion* I had the honour to present to the Royal 

 Society some results of an investigation made about electrical 

 conductivity of chemical compounds, and I then chiefly examined the 

 liquefied gases, pointing them out as very bad conductors. I have 

 since been engaged in studying another property of these substances, 

 and I have succeeded in determining in an experimental way their 

 refractive power. As in England and abroad several papers have 

 been subsequently published bearing on the relation between the 

 liquid and gaseous conduction of matter, and especially liquefied 

 gases present themselves well adapted to this kind of research, I hope 

 the Royal Society will consider my paper not devoid of interest, the 

 more so because our knowledge of their physical constants is some- 

 what limited. And though we possess numerous determinations of 

 the refractive power of a vast number of chemical compounds, still 

 ^increasing daily, I have found only very little information concerning 

 my subject, this being limited to sulphurous and prussic acid, that 

 are readily liquefied by cold and present no difficulty in manipulating. 

 Faraday in his extensive paper on liquefied gases, published in 1823, 

 when describing the properties of several of them, compares only 

 their index of refraction to that of water, calling it more or less, and 

 Brewster in 1826 mentioned in a communication to the Society of 

 Edinburgh the index of refraction of liquefied cyanogen as 1*316, 

 but without any remarks on the manner in which it was deduced.- 



I will commence this paper by describing the method I followed to 

 obtain the numerical values of the index of refraction of several 

 gases, liquefied either by pressure or by cold, and that enabled me to 

 surmount the difficulties resulting from high tensions and small 

 quantities of fluid substance, that may perhaps have kept back other 

 experimenters from this field of research. 



* " Proc. Eoy. Soc.," TO!. 25, p. 322. 



