A hydrometer is a measuring instrument that can be used to measure the density of a liquid. A hydrometer is usually a glass tube closed at the ends, the lower end of which is weighted with shot. The pipe floats vertically in the liquid. The areometer sinks less into a high-density liquid, more into a low-density liquid.

1. Prepare a hydrometer. Cut off part of the thin part of the pasteur pipette so that the length of the thin part is about $6cm$. Make a $5cm$ scale from a strip of graph paper and attach it to the neck of the pipette using clear tape so that the scale number “5” is near the thick part of the pipette and the number “1” is near the cut part of the pipette. Put enough shots in the pipette so that it floats deep in the tap water, so that the number "1" on the scale is at the water's edge. If this cannot be achieved, the areometer should float so that the water level is between the points "1" and "2" on the scale.
2. Construct the axes of the graph on graph paper. On the horizontal axis, mark the numbers of the scale sections 1 - 5. On the vertical axis, the density values ​​from $1g/c{m}^3$ to the value of the density of salt water.
3. Place the hydrometer in the tap water, take the hydrometer scale reading and put it on the graph. Place the hydrometer in the salt water, take the hydrometer reading and record it on the graph. Connect two points on the graph with a straight line.
4. Place the hydrometer in the unknown liquid and take the hydrometer reading. From the graph, determine the density of the liquid corresponding to the reading of the hydrometer.
5. Measure the volume and mass of an unknown liquid with a measuring cylinder and scale and calculate the density of the liquid.