| The classic way to measure the specific gravity of a liquid
is to use a hydrometer. One example is Nicholson's
Hydrometer, which uses a float that is always submerged to the same
depth by adding extra masses to it.
The more conventional hydrometer is a tube, weighted at the bottom to float upright, which sinks to various depths depending on the density of the liquid. The device used to measure the freezing point of antifreeze mixtures is a familiar example of a hydrometer used in an industrial setting. Brewers, wine-makers and distillers use hydrometers to measure the percentage of alcohol in their products.
This case of hydrometers at Virginia Military Institute was sold by James. W. Queen of Philadelphia. The largest hydrometer is marked "Beaume's Hydrometer, for liquids lighter than water/W. H. Pyle, Phila."
| Middlebury College has an unusual set of glass specific
gravity globes patented and [presumably] made by Lovi of Edinburgh.
The globes are weighted to give them an increasing series
of densities. It is sink or swim; the globes are placed one by one in the
liquid to determine which one has the density closest to the liquid, at
which point it has neutral buoyancy.