In science today, we made a hydrometer, which is a device that measures density of liquids. We constructed the hydrometers to see how dense water is compared to other liquids. 
To make the hydrometer, we cut off part of an eyedropper and put rocks into it until the bottom pocket was about halfway full. Then, we sealed off the top with clay and let it dry. Once it was made, we put it in various liquids and drew markings which showed how high the liquid went on the hydrometer. 
In the picture below, the top green line marks rubbing alcohol, the middle purple line marks tap water, and the bottom line marks salt water, which is the most dense of the liquids. 

When using the hydrometer, one would drop the tool in a liquid and check how low it goes into the liquid. The number or marking the liquid reaches shows its density.

One thing difficult about making the hydrometer was adding the weight. I used miniature rocks as a ballast, at putting them down the stem of the tool was challenging due to the stem's small size. In the future, this tool can be used for measuring any densities of liquids.