Chemistry. — “The Use of the Zwiss Waterinterferometer (RAYLEIGH- 
Lowe) for the Analysis of Non-Aqueous Solutions’. By Prof. 
Ernst CoHeN and H. R. Bruins. 
(Communicated at the meeting of June 25, 1921). 
1. Among the methods for a quantitative determination of the 
concentration of solutions, the optical methods excel the others in 
many cases in accuracy and rapidity of execution. With very careful 
regulation of the temperature (constant down to 0°.01) it is possible 
to determine with the most practical measuring instrument, the 
refractometer, indices of refraction accurate to 1 or 2 units of the 
fifth place of decimals, which about corresponds in aqueous salt 
solutions with an error in the determination of the concentration 
of 0.02 °/,. 
In some cases, e.g., for the analysis of exceedingly diluted solu- 
tions, this accuracy is, however, not sufficient. An instrument, which 
is eminently fit for such determinations, is the waterinterferometer 
according to RaYreiGH-Löwe, put on the market by the firm Zeiss. 
It enables us to measure the index of refraction of a solution down 
to 2 units in the 7 place of decimals, corresponding to an error 
in the determination of the concentration of at most 0.0002 °/,. 
This interferometer is, however, as its name indicates, constructed 
for the use of water as solvent, and all the investigations which 
have been executed by the aid of it up to now, concerned aqueous, 
or very diluted alcohol, solutions. 
In connection with an investigation, of which we hope soon to 
give further details, it was necessary to carry out accurate analyses 
of exceedingly diluted solu- 
tions in organic liquids. It 
then appeared that if the 
interferometer is to be used 
also in this case, a number 
of precautions must be ob- 
served, which will be set 
forth more at length in 
ay what follows. 
