GLASS-MAKING.
625
the end is drawn into a fine jet. This is hastily plunged beneath the surface of a Bath of pure mercury while the whole thermometer is still hot. As it cools, the air inside shrinks and the mercury
Fig. 5.—Calibrating Thermometers.
rises into the outer bulb. The permanent bulb is then carefully warmed, the tube being in a horizontal position so that the expanding air may freely escape. The tube is then held vertically
