56 J. H. Gladstone—Refraction Equivalents. 
But the law does not hold good in every instance. The 
refraction equivalents of the elements vary with a change of 
valency, or mode of combination, and thus the study of them 
is capable of affording valuable insight into the chemical 
structure of compound bodies. 
is fact has been recognized for several years, but the — 
researches of Briih], published about three years ago, drew 
far more attention to it, especially as he showed that wherever 
a carbon atom is in that condition which chemists often express 
twelve-month papers have appeared on this subject, not only 
in England, but in other countries, especially by Nasini of 
ome, Kanonnikow of the Kasan University, G. Quincke, and 
Bleekrode of the Hague. 
These recent papers have not only added largely to our data, 
but they have had an important bearing on several branches of 
the subject; for instance :— 
1st. They have thrown fresh light on the physical questions 
u 
. b] 
he specific refraction of eleven liquified gases, and has shown 
that it is the same for the liquid and the gaseous conditions, at 
least within limits that mav probably be attributed to the 
errors incidental to so difficult an enquiry. Kanonnikow has 
given additional proofs that the specific refraction of a salt or 
other solid body is not altered by solution. It has been shown 
more fully than before that the specifie refraction is a constant 
unaffected by change of volume due to*pressure. There is 
also an accumulated mass of evidence that this same property 
is not changed by ordinary chemical combination. 
2d. These investigations have rendered the determinations 
of the refraction equivalents more exact. Thus Kanonnikow 
has examined salts of the metals contained in the two first 
columns of Mendelejeff’s table, with results not differing widely 
from those previously obtained by the author; and Nasini has 
determined two values for sulphur. From these and other 
recent researches the author has been induced to revise the 
table printed by him in the Philosophical Transactions of 1869 
with the result given below.* 
3d. Deductions have been drawn as to the chemical constitu 
tion of various organic bodies. Some of these are at present — 
the subject of discussions by Flavitzky and others in various — 
* Since the paper was read at Montreal some of the atomic weights have been — 
ae in accordance with the recent determinations of Professor Clarke and 
