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Determining proof obscuration with a lab still


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I'm starting with 80 proof spirit, adding sugar and other flavors. to test the true proof i'm planning to use a small lab still. when looking at the gauging manual it says:

© Distillation method. Determine the apparent proof and temperature of the sample of spirits and then distill a carefully measured sample in a small laboratory still, and collect a quantity of the distillate, 1 or 2 milliliters less than the original sample. The distillate is adjusted to the original temperature and restored to the original volume by addition of distilled water. The proof of the restored distillate is then determined by use of a precision hydrometer and thermometer in accordance with the provisions of §13.23 to the nearest 0.1 degree of proof. The difference between the proof so determined and the apparent proof of the undistilled sample is the obscuration;

so if i start with 300 ml in the still i would collect 298 ml and adjust temperature, and add water to original quantity? it seems like it would be hard to leave only 1-2 ml in the still.

Thanks for any help,


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You just keep boiling until there is just 'gunk' left in the bottom of the boiler , then have fun cleaning it out. I think cleaning was discussed on this forum a couple of years ago. Clean looks nice but makes no difference to accuracy. To prevent foaming in the boiled add a small amount of soap. I use a couple of flakes of Lux, don't know if you have that in US. Brad, do you have an accurate VOLUMETRIC FLASK? For those who are unfamiliar with one, it has a comical flask and a long slender neck with an etched level mark. A parallel sided measuring cylinder is no where accurate enough.

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