“…These vary all the way from the simple, manually operated loop stirrer (151) to relatively complicated electromagnetic devices. Stirrers driven by an axle passing out of the cell are of two chief forms: the worm-shaped "blade" which gives thorough agitation to the whole mass within the cell (115,211), and propeller-type "blades" which impart a vigorous whirlpool motion to the cell contents (203). Among the electrically driven agitation devices several interesting versions also appear.…”