Rev. Rul. 58-352

Permission may be granted by Assistant Regional Commissioner, Alcohol and Tobacco Tax, to rectifiers to use the pycnometer distillation procedure in the determination of obscuration of proof provided the specific gravity before and after distillation is determined with the pycnometer. This procedure will be authorized only in those cases where the regional laboratory of the Internal Revenue Service has determined that the `solids method' as provided in section 235.570 of the Regulations relating to the Rectification of Spirits and Wines produces results which are inaccurate by 0.1 degree of proof or more.