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How to Determine the Alcohol Content of a Solution

Alcohol is usually found in some form of solution. A bottle of rubbing alcohol typically contains 70 percent isopropyl alcohol by volume. Beers usually have about 5 percent alcohol, while wines have a somewhat higher concentration of alcohol of 10 percent or more. High concentrations of alcohol destroy the yeast that promotes fermentation, so beverages with more alcohol than wine have to be distilled from a fermented liquid to increase the alcohol content. There are several methods of testing the alcoholic content of a solution. Most involve comparing specific gravities before and after fermentation or distillation, but some use other properties of liquids, such as their surface tension.

Things You'll Need

Specific gravity hydrometer
Vinometer
Flasks
Beakers
Heating apparatus
Clamp for holding flask over heat

Instructions

Distillation Method
- 1
  Pour some of the solution into a beaker large enough to hold the hydrometer. Set the hydrometer into the liquid and record the level at which the hydrometer floats. This tells you the specific gravity of the liquid before distillation.
- 2
  Measure 250 ml of the solution and pour the liquid into a flask.
- 3
  Heat the flask until the liquid begins to boil. Boil the liquid until half of it (125 ml) has evaporated.
- 4
  Allow the liquid to cool down. Add distilled water to the remaining liquid until the total volume is back up to 250 ml.
- 5
  Measure the specific gravity of the liquid with the hydrometer. Subtract the original specific gravity from the new specific gravity. Divide the result by 2.11 and multiply by 1,000.
Vinometer
- 6
  Fill the vinometer reservoir with the alcoholic liquid until some of the liquid exits from the other end.
- 7
  Turn the vinometer around so the reservoir faces down and allow it to drain. Do not tap it or do anything to speed the draining. The vinometer works by measuring the difference in surface tension between the solution being measured and that of pure water.
- 8
  Read the alcohol concentration level on the vinometer scale after the liquid has stopped draining.

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