XVII] 



DISTILLED LIQUORS 



247 



18 Immersion Refractometer Method. (Leach and Lythgoe*) — Tentative. 



Determine by the immersion refractometer at 20°C. the refraction of the distil- 

 late obtained in the determination of alcohol. If, on reference to the table under 

 19, the refraction shows the percentage of alcohol agreeing with that obtained 

 from the specific gravity, it may safely be assumed that no methyl alcohol is present. 

 If, however, there is an appreciable amount of methyl alcohol, the low refractome- 

 ter reading will at once indicate the fact. If the absence from the solution of re- 

 fractive substances other than water and the alcohols is assured, this difference in 

 refraction is conclusive of the presence of methyl alcohol. 



The addition of methyl alcohol to ethyl alcohol decreases the refraction in direct 

 proportion to the amount present; hence the quantitative calculation is readily 

 made by interpolation in the table under 19, using the figures for pure ethyl and 

 methyl alcohol of the same alcoholic strength as the sample. 



Example. — The distillate has a specific gravity of 0.97080, corresponding to 

 18.38% alcohol by weight, and has a refraction of 35.8 at 20°C. by the immersion 

 refractometer; by interpolation in the refractometer table the readings of ethyl and 

 methyl alcohol corresponding to 18.38% alcohol are 47.3 and 25.4, respectivelv, the 

 difference being 21.9; 47.3 - 35.8 = 11.5; (11.5 -^ 21.9) 100 = 52.5, showing that 

 52.5% of the total alcohol present is methyl alcohol. 



19 



Table 18. 



