Build Your Own Hydrometer

You can build your own simple hydrometer using the follow-ing readily available materials

• A large diameter drinking straw (the kind they give withslushies at the gas station work great)

• Aluminum foil

• A small bolt or screw

• Hot glue and a hot glue gun

• Sugar

• Water in a deep container, such as a tall vase or a bucket

• Sand

• A sharpie marker

To build your hydrometer, first hot glue a bolt with its threadsinserted in one end of the straw. Be sure to seal the openingof the straw around the bolt with glue so that no water canenter the straw from that end. Now place the straw, screw sidedown, into the water. It should float with about half the strawsticking vertically out of the water. If it floats too high, poura few pinches of sand into the open end of the straw to makethe hydrometer float lower in the water. Now plug the open endof the straw with a small piece of aluminum foil and cover thisplug with hot glue, again sealing the opening with the glue. Younow have a hydrometer, minus the meter.

To calibrate it, first float the straw in the water and markwith a sharpie the point where the water surface meets the straw.

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Now repeat this last step with various solutions of sugar wa-ter. Measure the volume of the water and then bring it to a boilin a pot. Add to the boiling water a quantity of sugar equal toroughly 5% of the volume of the water and stir until completelydisolved. Let this solution cool, then float and mark the hy-drometer again. This mark should be lower on the straw thanthe first.

Repeat this process by first adding enough water to the so-lution to bring the volume back to the original amount, boiling,and then adding another 5% portion of sugar and disolving.Cool the solution, then float and mark the straw again. Con-tinue adding marks until you are satisfied with your calibrationor until the sugar will no longer dissolve.

A note to those chemists out there: The sugar solutions thatyou are creating in this process are not actually very well de-signed. To do this more carefully, you would create solutionsthat are actually 5%, 10% etc sugar by weight. This requiresaccurate scales. It is also much easier to do if you create aseparate solution for each concentration. If this level of detailis required, it is recommended that you begin with somethingother than a plastic straw when building your hydrometer.

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