Learn How to Make a Hydrometer

A hydrometer is a very simple device that allows you to measure the density of various liquids relative to water. Hydrometers are used for a myriad of different purposes: they are used to measure the fat content of milk, the alcohol content of beer, wine, and spirits, and even the water content of urine to test for dehydration. To make a hydrometer, you need a drinking straw, some modeling clay, a nail, and an empty glass bottle.

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Steps

1. 1
   Build the base of the hydrometer. Take a lump of modeling clay and ball it around 1 end of the drinking straw, sealing it completely. Make sure that the ball is small enough to fit through the opening of the glass bottle.
2. 2
   Fill the glass bottle with water. You should fill it up nearly to the top.
3. 3
   Place the straw into the bottle of water. Put the clay-covered end in first, and allow the straw to come to rest at whatever depth it floats at. Your goal is to have the straw half submerged and half above water. You can add a little clay to the end to make it less buoyant, or take some clay off to make it more buoyant.
4. 4
   Add the nail to adjust the buoyancy if necessary. If the straw floats too high in the water with just the clay ball, slide the nail down into the straw to make it less buoyant. You can add an additional nail if the straw is still more than halfway out of the water.
5. 5
   Note the location of the water line on the straw. Once the straw floats about halfway in the water, let it come to rest. Note where the water line hits the straw.
6. 6
   Remove the straw from the bottle, keeping an eye (and a finger) on the point marking the water line's location. Mark this line with a marker on the straw and label it with the number "1." The line indicates a specific gravity of 1. Specific gravity is a measure of relative density. Water is assigned a specific gravity of 1 so that it can be used as a reference (for example, so you can know that whatever liquid you're measuring is more or less dense than water).
7. 7
   Empty the bottle and allow it to air dry. When it's dry, fill it again with olive oil. Insert the hydrometer (the straw) and note the level of the liquid against the straw. Remove the straw and mark this line on the hydrometer with a marker, labeling it with the number "0.91." This is the specific gravity of olive oil.
8. 8
   Repeat this process for several other common liquids to establish a scale on your hydrometer. For example, distilled vinegar has a specific gravity of 1.08, and rubbing alcohol has a specific gravity of 0.78. You can look up other specific gravity figures online.
9. 9
   Measure the density of other liquids with your hydrometer. If the liquid line falls halfway between the water mark and the olive oil mark, for example, the liquid has a specific gravity of about 0.96.

Tips

• Always exercise caution when working with flammable or dangerous liquids such as rubbing alcohol.

Things You'll Need

• Drinking straw
• Modeling clay
• Nail
• Glass bottle
• Water
• Marker
• Olive oil