Studies on the Dichromate Method of Alcohol Determination

Abstract

A highly reproducible method for determining the alcoholic contents of wine is reported. It is shown that results of the dichromate method are on the average 0.24% alcohol higher than the results of densimetric measurements on 200 ml wine distillates. Dichromate reaction and pycnometer give identical results on alcohol-water mixtures. Micro-steam distillates as used in the dichromate method, and 200 ml distillates as employed for densimetric determinations, give identical alcohol results by the dichromate reaction. Fresh 200-ml wine distillates are found to contain small amounts of a highly volatile component other than ethanol. Through a compensation of errors, this component brings about a fortuitous agreement between dichromate alcohols and pycnometer alcohols of the fresh distillates. After aeration of the distillates, the usual dichromatepycnometer differences appear. Volatile acid and sulfur dioxide in 200-ml distillates depress pycnometer and hydrometer alcohols by an average of 0.11% alcohol but leave dichromate results essentially unaffected. Forty % of the remaining dichromatepycnometer difference of about 0.13% alcohol is shown to be caused by a substance which depresses pycnometer alcohols but leaves dichromate alcohols essentially unaffected. It is thus demonstrated that about two-thirds of the observed dichromate pycnometer or hydrometer differences are due to influences which cause the densimetric results to be in error but do not appreciably affect dichromate results. This establishes that the dichromate method reflects the true alcoholic content of wines more closely than standard pycnometer or hydrometer procedures.