Hydrometer, Waterloo, Ontario; circa 1975; glass, weight, paper; 87.29.1.
Hydrometer, Waterloo, Ontario; circa 1975; glass, weight, paper; 87.29.1. |
A hydrometer was a device used for determining the density, or specific gravity, of water / spirit mixtures for excise purposes, whereby taxes were levied according to alcoholic strength or "proof". The distiller and the government excise officer used a hydrometer to measure the percentage of alcohol throughout the stages of distillation and maturation. Readings taken from the hydrometer were used, together with standard published tables, to calculate the amount of proof spirit. A hydrometer is calibrated to the density of water at 1.0.
 Hydrometer Tables, 82.1.645. View Image Notes in New Window |
As temperature affects the density of a liquid, the distiller first recorded the temperature of the water / alcohol mixture. The hydrometer was then placed in the mixture and, when using a brass hydrometer, additional weights were added beneath the bulb until the level of the liquid rested within any part of the graduated stem. The numbers on the additional weight(s) and on the hydrometer stem were added together to obtain a specific gravity reading. Using hydrometer tables, the distiller determined the proof of the mixture by locating the specific gravity reading for the given temperature of the mixture. Over time, hydrometers with limited ranges were developed to obtain more precise readings. The glass hydrometer above provided accurate readings in liquids at 16.7 degrees Celsius.