116 
rays is further quite as in fig. 1. The lower part of the beam leaving 
lens L, however, does not traverse the vessels, but passes under 
them through the water in reservoir W, which serves as “Temperier 
bad” of the vessels. Also these rays of light interfere in O, where 
they form a fixed image lying below the former, separated from it 
by a narrow line, and serving as “point de repere” of the zero 
position. Both images are examined by means of the greatly magni- 
fying cylinder ocular BE. The compensator plate P, is rotated by 
means of a lever, which is worked by a micrometer screw with 
drum D; on this drum a seale is drawn of a hundred divisions. 
With the instrument used by us one interference band corresponds 
to 21 scalar divisions. The uncertainty in the adjustment with regard 
to the coinciding of the two interference images is, after some 
practice, about half a scalar division. 
For the analysis of solutions one has only previously to construct 
a gauging curve comprising the concentration region used. On the 
shifting of the central band which seems to take place in this case, 
compare ADAMS '). 
3. When it is tried to analyse in this way solutions in organic 
liquids (for which, of course, the use of so-called “säurefest ver- 
schmolzen” vessels consisting entirely of glass, is necessary) the 
following phenomena are in general observed in the interferometer. 
The upper interference image is blurred and shifted with regard to 
the lower one. The bands are permanently oblique and curved, or 
for a long time. Shaking of the liquid in the vessel (by tapping 
against the interferometer) indeed promotes the rapidity with which 
the image is formed, but reproducible results cannot be obtained, 
and after some time the lines become again shifted and curved. 
The causes of these deviations, which render an accurate measure- 
ment of course impossible, appeared to be due to the following 
circumstances : 
A. the nature of the bath-liquid. 
B. the influence of the temperature on the index of refraction 
of the solvent; 
C. evaporation and distillation against the glass covering-plates 
of the vessels ; 
D. absorption of water during the conveying and the staying of 
the liquid in the vessels. 
4. Ad A. The nature of the bath liquid. 
Compared with by far the majority of the organic liquids the 
1) Apams, Journ. Amer. Chem. Soc. 37, 1181 (1915). 
