Twaddell - Hydrometer, 6" glass

Accession #: 2010016

Complete, in cardboard box. Calibrated from 74 - 102°. Engraved: 'T. Dryden Ltd.' Twaddell: A form of hydrometer for liquids heavier than water, graduated with an arbitrary scale such that the readings when multiplied by .005 and added to unity give the specific gravity. The scale was intended for use by unskilled persons. The numbers are obtained from specific gravity numbers by dropping the decimal and the preceding numeral, reading the following numbers to two significant figures and doubling them. Thus, 1.35 sp. gr. becomes 70° Twad. In order to change degrees Twaddell into specific gravity, multiply by 5, add 1,000 and divide by 1,000. 19th-20th century, mostly used in England, for example in the leather industry to check tanning solutions, and for sulphuric acid and milk. Abbr., °Tw.

Charles Macintosh (Sir Walter Scott's "Webster Charlie"), requiring ammonia for bleaching and dyeing, procured a fleet of horse-drawn carts, duly despatched to Edinburgh and Glasgow to buy the contents of chamber pots. There were social consequences. The urine was no longer poured from tenement windows on the heads of passers-by. Purchasing the liquid gold by volume encouraged fraudulent dilution on the part of domestic suppliers until a Glasgow instrument maker named Twaddell came up with a robust hydrometer.

Dimension: 173 x 16.8 mm diameter

Acquired: 15/03/2010