This work presents the definition of density and describes the densitometer, apparatus which measures density of pure liquids or solution without the use of a balance. The conception of the densitometer is based on the Archimedes's Principle (flotation). The use of this instrument was greatly accelerated in the XVII century. Two models were proposed: constant weight and constant volume. Its basic format has not changed much over the last 250 years. The most interesting evolution was the change of the ballast: from liquid mercury to solid lead balls fixed by a resin. The densitometer is a cheap and practical apparatus to make some simple experiences that show the importance of the density in chemistry and physics and in our everyday life, as well as in the quality control of some goods (like ethanol and beverages) via density measurement.
densimeter; density; buoyancy
