Hydrometers are buoyancy devices used to determine the specific gravity of a fluid. The Sykes hydrometer received legislative approval in England in 1816 and remained the legal standard until 1907 but was made and used in the wine and spirits industries to the mid-twentieth century. Typically, hollow bulbs made of brass with an attached rod for holding weights, hydrometers often come in wood boxes with brass or ivory backed thermometers, glass flasks, scales and magnifiers. Some hydrometers are simply glass tubes with a weighted bulb of mercury or lead shot and a graduated stem that sinks up to a mark that indicates the fluid’s density.