the temperatures given may be looked upon as exact to 0° 
J, H, Long—Indices of Refraction of Compound Ethers. 279 
Art. XXXIIL.—On the Indices of Refraction of certain Com- 
pound Ethers ; by Joun H. Lone. 
ABOUT two years ago, while at work in the laboratory of the 
stances were being used by Herrn Emil Elsiisser for the deter- 
mination of specific gravity and coefficient of expansion, an 
his results I have made use of in the calculation of the tables 
ound below. 
_ Other duties prevented the publication of my results at the 
time, but the elegant work of Briihl,* which has since appeared, 
having added a new interest to the subject of refraction, I deem 
't not too late to make them known now. The method em-_ 
ployed was essentially that of Landolt.t A large Meyerstein 
pee mets, kindly loaned me by Professor v. Reusch of the 
tibingen physical laboratory, permitted results exact to four 
decimal places of n (as scp latisaek below) to be readily obtained. 
The fifth decimal place is in most cases uncertain. ° 
. +48 Source of light I used the sodium flame and the refrac- 
tive indices for the D line were determined for several differ- 
ent temperatures. This was accomplished as follows: The 
hollow glass prism containing the liquid to be examined, 
together with its metallic support, was placed on a hot iron 
Plate and left there until the temperature of the liquid had 
risen (in most cases) to about 30° C., as shown by the small 
thermometer firmly secured by a cork in the orifice of the prism. 
e 
room. The thermometer used had been previously carefully 
f “pared with a normal thermometer in the possession of Pro- 
t Meyer and a table of corrections thus obtained, oy cea 
d The indices were determined by the method of minimum 
eviation, according to the formula 
ln W. Brihl: Die chemische Constitution organischer Kérper in Beziebung zu 
ren Dichte u, Vermégen d. Licht fortzupflanzen. Liebig’s Annalen, cc, 139; 
oe 255 and 363. See also this Journal, Jan., 1881, page 70. 
8. Ann., Bd. exvii, 353. 
