- 1). Roll a small piece of clay into a ball one centimeter around.
- 2). Plug one end of the straw with the clay ball.
- 3). Fill a graduated cylinder with water to the 100 ml line.
- 4). Place the straw into the graduated cylinder, with the clay ball at the bottom and one inch of the straw sticking out of the water. Add or remove some of the clay ball to make the top of the straw stick out one inch. Use a ruler to help you.
- 5). Mark the straw with a permanent marker where the top of the water hits the straw. This is line "0" representing pure water without salt.
- 6). Take the straw out of the water.
- 7). Add one gram of sea salt into the cylinder and stir it until it dissolves.
- 8). Put the straw back in and mark it where the water and straw meet. This line is "10," because the solution has a salinity of 10 o/oo (10 pounds of salt per 1,000 pounds of water).
- 9). Keep adding a gram of salt and re-measuring the straw, making marks with multiples of 10. There should be lines with numbers all up and down the straw when you're finished.
- 10
Wash off your straw hydrometer. Place it into the fluids that you want to test and make a note of where the water touches the straw.
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