# How Do I Use a Hydrometer to Find Alcohol Percentage?

Written by frank b. chavez iii
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A hydrometer is a device designed to measure the specific gravity of a liquid. It consists of a closed glass tube with a bulb at one end filled with mercury or lead shot so that it will float upright in the liquid. It is marked with a scale that indicates how much lighter or heavier the liquid is than water. The design of the hydrometer is based on the Archimedes' principle and so it can also be used to determine density. Hydrometers are commonly used in brewing and wine making to determine the percentage of alcohol in a given beverage. Many hydrometers have both a potential-alcohol scale and a specific-gravity scale.

Skill level:
Moderate

• Hydrometer
• Test tube
• Pencil
• Paper
• Calculator

## Instructions

1. 1

Collect, carefully, some of the liquid to be tested into a test tube large enough to allow the hydrometer to float in easily.

2. 2

Lower the hydrometer into the liquid. Let it float.

3. 3

Record the percentage of potential alcohol by volume indicated by the hydrometer.

4. 4

Allow the liquid to ferment.

5. 5

Collect a second sample and record the percentage of potential alcohol by volume indicated by the hydrometer.

6. 6

Subtract the second percentage from the first percentage. For example, if the first reading was 15 per cent and the second reading was 5 per cent, then the percentage of alcohol by volume would be 10 per cent.

1. 1

Record the specific gravity indicated by the hydrometer.

2. 2

Allow the liquid to ferment.

3. 3

Take a second reading with your hydrometer. Record the new specific gravity.

4. 4

Subtract the second specific-gravity reading from the first.

5. 5

Divide the difference by 7.36. For example, if the first specific gravity was 1,080 and the second was 995, then the percentage of alcohol would by 11.55 per cent.

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