Having just revisited this topic, as there were so many different sizes, going down to 'powder' (almost), then they could have been what became known as Ballotini beads. These had a wide range of uses, such as a coating for reflective road signs, cinema screens, and the largest known were used for storing blood plasma - not sure what size these were, but I imagine the idea was to prevent coagulation.
Sizes quoted on the original patent of 1943 (US2334578, R H Potters) were 0.008-in to 0.055-in*. However, all this is superfluous as it post-dates the Molineaux Webb spheres, unless MW never patented their idea?
*In Monopoly money that's 0.2032 to 1.397mm