How to Build a Hydrometer
Seal off an end of a soda straw., Fill a narrow jar or graduated cylinder partially with water., Put the straw in the water, sealed side down., Mark the place on the straw where it touches the surface of the water with a permanent marker., Remove...
Step-by-Step Guide
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Step 1: Seal off an end of a soda straw.
You can plug the end with modeling clay, plasticine (Play-Doh or Cranium Clay), or a wad of chewed gum.
Be sure to use something that won't let water seep through it, and use a piece large enough not to let water seep past it. -
Step 2: Fill a narrow jar or graduated cylinder partially with water.
If using a graduated cylinder, fill it to the 100 milliliter line.
If using a narrow jar like an olive jar, fill it with 100 ml (0.42 cup) of water and mark a reference line on the outside of the jar with a permanent marker. (If you don't have a measuring cup with metric measurements, use 1/2 cup of water.) You can use either distilled or tap water, but whichever you use, use the same type of water from the same source throughout this project.
The water will form a curved arc called a meniscus.
Where the bottom of the arc falls is considered the correct point to read the water level on a graduated cylinder or to mark the water line on an unmarked jar. , The straw will serve as your hydrometer.
Note how far up the straw pokes from the top of the jar or graduated cylinder.
You want the open end of the straw to poke no more than 1 inch (2.5 cm) from the top of the container of water.
If it does poke up more than this, add weight to the straw to keep it from floating up too high and flipping onto its side.
You can add weight either by adding more clay, plasticine, or gum to the outside of the straw at the sealed end, or you can drop small weights such as BBs, split shot sinkers, small nails, or pebbles down the inside of the straw until it floats at the right level. , This point is your zero line. , Your hydrometer is now calibrated for "pure" water (either distilled or regular tap water).
From here, if you wish, you can mark lines above and below this line.
Ideally, each line should be 1 mm (about 1/32 inch) apart, or at least as close as the width of the point of your marker will allow.
You may want to use multiple colors for your lines, such as red for the zero and 10-mm lines, and black for the lines between them. -
Step 3: Put the straw in the water
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Step 4: sealed side down.
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Step 5: Mark the place on the straw where it touches the surface of the water with a permanent marker.
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Step 6: Remove the hydrometer from the water.
Detailed Guide
You can plug the end with modeling clay, plasticine (Play-Doh or Cranium Clay), or a wad of chewed gum.
Be sure to use something that won't let water seep through it, and use a piece large enough not to let water seep past it.
If using a graduated cylinder, fill it to the 100 milliliter line.
If using a narrow jar like an olive jar, fill it with 100 ml (0.42 cup) of water and mark a reference line on the outside of the jar with a permanent marker. (If you don't have a measuring cup with metric measurements, use 1/2 cup of water.) You can use either distilled or tap water, but whichever you use, use the same type of water from the same source throughout this project.
The water will form a curved arc called a meniscus.
Where the bottom of the arc falls is considered the correct point to read the water level on a graduated cylinder or to mark the water line on an unmarked jar. , The straw will serve as your hydrometer.
Note how far up the straw pokes from the top of the jar or graduated cylinder.
You want the open end of the straw to poke no more than 1 inch (2.5 cm) from the top of the container of water.
If it does poke up more than this, add weight to the straw to keep it from floating up too high and flipping onto its side.
You can add weight either by adding more clay, plasticine, or gum to the outside of the straw at the sealed end, or you can drop small weights such as BBs, split shot sinkers, small nails, or pebbles down the inside of the straw until it floats at the right level. , This point is your zero line. , Your hydrometer is now calibrated for "pure" water (either distilled or regular tap water).
From here, if you wish, you can mark lines above and below this line.
Ideally, each line should be 1 mm (about 1/32 inch) apart, or at least as close as the width of the point of your marker will allow.
You may want to use multiple colors for your lines, such as red for the zero and 10-mm lines, and black for the lines between them.
About the Author
Teresa Armstrong
Enthusiastic about teaching cooking techniques through clear, step-by-step guides.
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