A hydrometer is a simple device that allows you to measure the density of various liquids compared to water. Hydrometers are used for many very different purposes: they are used to measure the fat content in milk, the alcohol content in beer, wine or spirits, and even the water content in urine to check for dehydration. To make a hydrometer, you will need a tube along with some wax and paper.
Steps
Part 1 of 3: Making the hydrometer
Step 1. Mark your intervals, use a pencil to mark the edge of a piece of paper
Make a mark every 2 millimeters, you will need a ruler to measure exactly 2 millimeters.
Make enough marks so that it roughly measures your entire index finger
Step 2. Cut a strip of the paper
Cut the side of the paper that you marked to get a long, thin strip. This will allow you to slide the paper into a piece of the glass tube. Also, this tube should be open at both ends.
Step 3. Insert the paper strip into the glass tube
Use a tube that is about the length of a drinking straw. If you do this at home and you don't have a glass tube, use a clear straw (if you use a colored straw, it will be difficult to read the marks you made on your papers).
Step 4. Seal one end of the tube
Melt wax or glue to secure the papers on one side of the tube. Then use the glue or wax to make an airtight seal on that part of the tube. Leave the other end unsealed.
Step 5. Cut off any excess paper
The strip of paper should be flush with the bottom of the tube. Use scissors to cut the strip and be careful not to yank or toss it, or you could break it.
Part 2 of 3: Calibrate the Gauge
Step 1. Add water to a measuring cylinder
It is not important how much water you add; about 100 milliliters will be enough. Make sure the water is as pure and free of contaminants as possible.
Any translucent bottle, like a soda bottle, will work too
Step 2. Add weight
Put 4-5 grams of metal in the tube. This will reduce the tube's ability to float enough that part of the tube will sink. This is necessary to use the instrument for measurement purposes.
A source of metal that you have within reach is a small nail
Step 3. Insert the glass tube or straw into the water
The sealed part should go underwater first. Avoid getting water into the tube, as this will change the tube's floatability and wet your paper.
You can change how much the tube floats or sinks by adding or removing weight (metal)
Step 4. Mark the water level
Use a permanent marker to draw a line on the side of the tube exactly at the water level. This will serve as a reference point for the instrument and will be marked as 1, 0. This mark indicates how far the tube sinks into a liquid that has the exact density of water.
Part 3 of 3: Determine the Relative Density of Other Liquids
Step 1. Immerse the hydrometer in liquids
Choose a liquid to test and then put about 100 millimeters of that liquid in a glass. Finally, put the hydrometer inside the glass.
Step 2. Mark the liquid level
In the same way that you marked the level of the surface of the water, make a mark to show how high this liquid reaches in the instrument. You can know a little about relative density just from this little initial mark. For example, if this new mark is above the 1.0 mark, it means that the liquid is less dense than water. If the mark is below 1.0, then it means that the liquid is denser than water.
Less dense liquids will cause the tube to sink more and denser liquids will cause the tube to sink less, due to Archimedes' principle: the buoyant force of an object immersed in water is equal to the weight of the water that was displaced
Step 3. Find the relative density
If you want a more specific specific gravity, you can calculate it mathematically. Measure the distance from the bottom of the tube to the 1, 0 mark and the distance from the bottom of the tube to the new mark. Divide the two distances and the result will be the relative density of the liquid compared to the water.
- For example, if the distance from the bottom of the tube to the 1.0 mark is 5 millimeters and the distance from the bottom of the tube to the new mark is 4.5, you would divide 5 by 4.5, which will give you would result in a relative density of about 1.1. Liquid is 1.1 times denser than water.
- Conversely, if the distance from the bottom of the tube to the 1.0 mark is 5 millimeters and the distance from the bottom of the tube to the new mark is 5.5, you would have to divide 5 by 5.5. This will give as a result a relative density of about 0.9. Liquid is 0.9 times denser than water.