We all know that blood is thicker than water, gas floats on the water and it is easier to float in salt water than in fresh water. Why is that? The density of these liquids is different. What a difference? That’s where a hydrometer comes in! A hydrometer is used to measure the density or thickness of liquids. The measurement is expressed regarding density. For example, the specific gravity of water is 1. A hydrometer is numbered from top to bottom, with the smallest numbers on the top. A hydrometer must float in a liquid, with a portion of the hydrometer above the surface of the liquid and a part of the hydrometer under the surface of the liquid.
- Cap one end of the straw using a centimeter-sized ball of clay.
- Place the small-headed nails in the straw.
- Fill the clear cup with water.
- Place the straw in the water.
- Note location of the water line on the hydrometer.
- Remove the straw from the water, keeping your fingers at the water line.
- sec off the straw.
- Mark with a permanent marker of the location of the freshwater line on the straw. Allow to dry and put back into the water to ensure the mark is at the water line.
- Place the straw next to the ruler. Mark on the straw in increments of 1 cm on each side of the fresh watermark, along with the entire length of the straw. Differentiate these marks from the fresh watermark by making them shorter marks.
- Test your hydrometer in other liquids. If the density meter sinks lower in the liquid, you measure a liquid that is less dense than water. If the densimeter does not run as low in the liquid, you measure a liquid that is denser than water.
Tips and Warnings
- When you look at the water line around the straw, you will see that it raises the straw a little. This is known as the meniscus. The water line that you use to measure with is the horizontal line of water at the base of the meniscus.
- Hydrometers are numbered with the highest number at the bottom of the hydrometer and the lowest number (negative) at the top of the hydrometer.
- If your hydrometer runs down the bottom of the water cup, remove one of the nails or add water until the hydrometer is floating in the water. If you remove one of the nails, do not put it back into the straw when measuring other liquids.