The hydrometer is a device used in the direct evaluation of the specific gravity of a particular liquid. The hydrometer was invented by Antoine Baume, chemistry professor at Ecole de Pharmacie in the year 1768. Baumie invented two hydrometers; one measuring fluid denser than water and the other one for liquids less dense than water. The hydrometer is usually made of a thin glass tube which closed at both ends (Holmes, p.156). One of the ends is distended into a bulb which contains mercury or fine lead shot which enables the device to uprightly float in a fluid. The glass tube has a scale calibrated so that the point on the scale which coincides with the surface level of the liquid the hydrometer is floating on, indicates the specific gravity of the fluid, which is the density of the liquid as compared to water.
The hydrometer is banks on Archimedes' principle in its operation. The floating level of the hydrometer solely depends on the liquid’s density. Therefore, the floating level may be used to determine the specific gravity and density, which it is, has proportionality with. Hydrometers on sale are commonly calibrated for room temperatures, 20 degrees Celsius (68°F), or for 4 degrees Celsius (39.2°F) (Holmes, p.157). Since there are variations in the depths to which the hydrometer sinks in dense and less dense liquids, one type is meant to be used for less dense liquids and another for dense liquids, with the reference density being that of water.
The hydrometer has many applications ranging across, many fields. One instance is the case of the bulb hydrometer which is composed of small commercial hydrometer inside a bigger glass tube into which the liquid to be measured is drawn by rubber bulb. The bulb hydrometer used to determine the specific gravity of the sulphuric acid solution in vehicle or car batteries. The other application of the hydrometer is measuring the alcohol content and sugar concentrations of homemade drinks (Son et.al, p.7). The process involves taking readings before fermentation and after, the variation being the alcohol content. The hydrometer is also used to evaluate the salinity of water. The marine aquarist determine the accurate density using the hydrometer which has been calibrated for use in marine aquarium (Blasiola, p.30).
Blasiola, George. The Saltwater Aquarium Handbook. Hauppauge, N.Y: Barron's, 2000. Print.
Holmes, Frederic L. Instruments and Experimentation in the History of Chemistry. Cambridge, Mass. [u.a.: MIT Press, 2002. Print
Son, H.S, Y.S Hong, W.M Park, M.A Yu, and C.H Lee. "A Novel Approach for Estimating Sugar and Alcohol Concentrations in Wines Using Refractometer and Hydrometer." Journal of Food Science. 74.2 (2009). Print.