Your bulb should be small enough to float freely in your graduated cylinder. Standard hydrometers are 20. 32 centimetres (8. 00 in) in overall length, including both the stem and the bulb. Metal weights can be purchased at home hardware stores and should be 4 grams (0. 14 oz) and small enough to fit into a straw. Clay can be purchased from craft stores or online suppliers. Purchase a 250 millilitre (1. 1 c) or 500 millilitre (2. 1 c) graduated cylinder (online or from an office supply store) so that you don’t risk it overflowing. For glass jars, purchase a clear 16 ounce (473 mL) clear glass type from a big-box store.
You can use either distilled or tap water. Whichever you use, be sure to use the same type of water from the same source throughout the project. When reading the water level on a graduated cylinder or marking your jar, always measure from the bottom of the meniscus—curved arc created on the water’s surface.
You may be able to find steel parts such as steel disc blanks or washers that match these specifications without having to cut the metal yourself. Look at your local hardware store or check online. Since sheet lead is very thin, you can usually bend it with your hands or with a pair of pliers. Be sure to wear protective gloves to prevent any accidental cuts when bending. Use a gram scale for measuring weight. These can be purchased from convenience stores, big-box stores, and online suppliers.
Test your silicone on a piece of scrap to get a feel for the flow of the sealant before applying it to your straw. Use as little silicone as possible to minimize weight.
After attaching the clay, hold the straw up in the air vertically and make sure that the ball doesn’t fall off.
The open end of the straw shouldn’t extend more than 1 inch (2. 5 cm) from the top of the container of water. If it pokes out more than this, add weight to the straw to keep it from floating up too high and flipping onto its side. For additional weight, you can stick clay to the outside of the straw at the sealed end, or drop split shot sinkers, small nails, or pebbles down the inside of the straw until it floats at the right level.
Use multiple colors for your lines, such as red for the zero and 10 millimetre (0. 39 in) lines, and black for the lines between them. If you can’t mark the lines 1 millimetre (0. 039 in) apart, aim for them to be at least as close as the width of the point your marker will allow. Take note of how far apart each line is and make sure all of them are equal distances apart.
If the straw doesn’t align with the chart properly, wipe down the straw, attach another weight, and create another calibration line. Be sure that no water is in the straw to throw off the calibration. Print the calibration chart here: http://www. potteryatoldtoolijooaschool. com/floating_straw_hydrometer. pdf
If you don’t have a calibration chart, measure the distance from the bottom of your straw to the water-level marking in millimeters—this length will be called “x. " Using a calculator, calculate “x/1. 1”, which will tell you, in millimeters, where the 1. 1 calibration mark should go. Use the measurement lines you drew onto the straw to help guide your markings and repeat the “x/number” calculation for each calibration mark. [9] X Research source
Adding 10 grams (0. 35 oz) of salt at a time is standard. If you want to dilute your solution and decrease its density, add more water.
Always clean out your container after filling it with substances other than water to remove any residue. Hydrometers measure specific gravity. Since specific gravity is dimensionless, there is no unit of measurement.
