watch-glass

noun

a curved glass disc that covers the dial of a watch
a similarly shaped piece of glass used in laboratories for evaporating small samples of a solution, etc

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Examples from the Web for watch-glass

Historical Examples of watch-glass

A bit of the culture is removed and placed in a watch-glass of water.
The Fundamentals of Bacteriology
Charles Bradfield Morrey
The edges are now ground off, and the watch-glass is complete.
Harper's New Monthly Magazine, No. IX.--February, 1851.--Vol. II.
Various
A little of the supernatant ether is now removed to a small glass capsule or watch-glass, and allowed to evaporate spontaneously.
Cooley's Cyclopdia of Practical Receipts and Collateral Information in the Arts, Manufactures, Professions, and Trades..., Sixth Edition, Volume I
Arnold Cooley
In form, it is circular, convexo-concave, and resembles a watch-glass.
A Treatise on Anatomy, Physiology, and Hygiene (Revised Edition)
Calvin Cutter
There's no more glass about you than there is about me—and that is my watch-glass.
Wilson's Tales of the Borders and of Scotland
Various