This project shows us how to use a glass hydrometer. The hydrometer is really just a glass tube at least 1/4 inch in diameter (about the size of a pencil), that is open at both ends.

We have a glass container of water, and we will put the tube into it so that the tube is standing up (of course, we'll hold onto it to keep it straight). The tube is longer than the water is deep, so that part of the tube sticks out from the surface of the water. The tube is full of water, also, and it is at the same level as the water on the outside of the tube.

Now, we'll pour another liquid into the tube, until it forces water out of the bottom end of the tube. Since the new liquid is lighter than the water, it doesn't go down all the way to the bottom - it floats. Now, look at where the level of the new liquid inside the tube is, and compare it to the level of the water outside of the tube. The difference in height is a measure of the specific gravity of the water.

If we want to use a liquid that is heavier than water, we fill the container with the other liquid, and pour water down the tube until the other liquid is forced out the bottom of the tube.

We can mark the tube at the place where the water level is and again at the place where the other liquid is, then divide it into tenths. See if the glass hydrometer shows the same measurements as the pencil hydrometer or the straw hydrometer used in another hydrometer project.