Chemistry and Physics. 73 
method illustrated by table I, Bruhl has determined the effect 
of the double and treble links in the case of carbon, and of the 
double links in the case of oxygen, on the atomic refracting 
ower, and has thus obtained the data for the following table. 
n this table C’ C’ C’” indicate carbon atoms singly, doubly and 
trebly linked with each other, and O” an atom of oxygen doubly 
linked to an atom of carbon, and in order that the values given 
may be used in calculating the molecular refractive power of 
organic compounds it must be further noticed that the value for 
ie 
the group —C— is 5+3°4 = 84 and that for the group —C= (yas 
is 2 XK 6°15 = 12°38. 
TABLE LY. 
Ta TA 
C 5°00 4°86 
sa 615 5°86 
ees 5°95 5°76 
0” 2°80 o43 
0” 3°40 3°29 
H 1°30 1°29 
Cl 9°80 
Br 15°30 14°75 
24°90 23°55 
N’ 5°80 5°35 
not only the parafines and their derivatives in which the carbon 
atoms are usually singly linked, but also the olefines, the acetylenes 
and the aromatic bodies, in which the complexity of the structure 
1s Increased by double or treble links. In the original papers such 
results are compared with the molecular refractive powers calcu- 
an 
Cauchy’s formula so as to eliminate the effect of the irregular 
Seernye powers of the substances compared. e have not 
details of the investigation which involve many incidental points 
be sufficient to say that the papers 
show that the work has been done with all the care and refine- 
ments of which the methods used are capable, and limit ourselves 
to a description of one only of the important conclusions to which 
) ations points. 
t is obvious that, when a question in regard to molecular 
structure turns on the existence or absence of multiple bonds, the 
calculated molecular refractive power will not be the same in the 
two cases and then the index of refraction and the density of the 
substance may give us the means of testing our hypothesis. As 
18 well known there has been a question in regard to the molecu- 
