Alcohol, immersion refractometer tables

The alcohol content of the distillate may be checked by determining the immersion refractometer reading and obtaining the percentage of alcohol from Table A6. 

Determine by the immersion refractometer at 20° the refraction of the distillate obtained in the determination of alcohol. If, on reference to the table under A6, the refraction shows the percentage of alcohol agreeing with that obtained from the specific gravity, it may be assumed that no methyl alcohol is present. If, however, there is an appreciable quantity of methyl alcohol, the low refractometer reading will at once indicate the fact. If the absence from the solution of refractive substances other than H2O and the alcohols is assured, this difference in refraction is conclusive of the presence of methyl alcohol. 

The B.P. requires the final distillate to comply with purity tests for freedom from methanol and / opropyl alcohol. The refractive index of the distillate, when determined with an immersion refractometer, should not differ by more than 0 00007 (equivalent to 0 2 on the immersion refractometer scale) from that corresponding to the specific gravity of the distillate (see table). If it differs by more than 0 00007 the process B must be used... 

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