Popular Science, joulukuu 1921
Is pure radium really used in making the luminous figures on watch-faces? If so, how is it that they can be sold so cheaply? - E. H.
No, the material on luminous dials consists of a minute quantity of a radium salt mixed with some phosphorescent substance as sulphide of zinc or barium. Such a combination will glow more in the dark than would radium, which, in its pure state, is not luminous. The reason that watches with luminous figures can still be sold cheaply is due to the fact that only an infinitesimal quantity of radium salts is needed to impart unusual luminosity to the inert salts of barium and zinc.
In dyeing cloth at home it is necessary to buy and use one kind of dye for woolens and silks and another for cottons. Why cannot the same dye be used for both fabrics? - I. S. E.
Wool and silk are animal origin. Cotton is from a plant and consists principally of cellulose. Being of animal origin, woolens and silk are more active chemically than cellulose products, and will combine directrly with many dyes. But cotton cloth demands a substance known as a mordant before dyes will affects it. Aluminum hydroxide is one of the mordants that make possible cotton dyeing with special basic dyestuffs.