Specific gravity beads

Specific gravity beads are used to measure the density of a liquid at a given temperature and thus its alcohol content. These beads (pictured here in their circular wooden box) were made around 1805 by Antoni Galletti, a Glasgow-based scientific instrument maker who originated from Milan and emigrated to Scotland in the late 18th century.

The set has 12 glass beads, marked 22 to 34. The paper label inside the lid includes the words 'Made and Sold, wholesale and retail, by A./ Galletti, No 10, Nelfon Street, Glafgow'. The beads were of different buoyancy, and were successively dropped into a liquid in sequence until just one sank, providing the measurement as marked.

From the late 18th century, immigrant Italians arrived in Britain in some numbers. The particular trades they brought with them were glass-blowing and carving and gilding, which extended naturally into looking-glass and barometer manufacture.

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