practically all air has been sucked by a mercury pump before sealing.
The manufacture of glow-lamps is now an important industry. One brand of lamp20 is made as follows:—First, cotton-wool is dissolved in chloride of zinc, and forms a treacly solution, which is squirted through a fine nozzle into a settling solution which hardens it and makes it coil up like a very fine violin string. After being washed and dried, it is