What is NOT needed to make a salinometer/hydrometer?

A salinometer or hydrometer is an instrument used to measure the specific gravity or salinity of liquids, particularly water. To construct one, a soda straw can serve as the float, which enables the device to float on the surface of the liquid. Modeling clay can be used to create a seal or weight that helps calibrate the hydrometer to ensure it floats at the correct level depending on the liquid's density. Water is obviously essential as it is the medium that is being tested for salinity.

Plastic tubing, while possibly useful in some forms of designs or setups for similar experiments, is not a necessary component for constructing a basic salinometer or hydrometer. Many effective versions do not require tubing at all, thus making it the correct answer to the question. The other materials are crucial for the construction and function of the device, highlighting that plastic tubing does not play a vital role in the process of measurement for salinity or specific gravity.