GLASS-MAKING.
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it must displace its own weight of the supporting fluid. If, then, a float of invariable weight be immersed in a liquid, the depth to which it sinks will be a measure of the specific gravity of the
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/PSM_V39_D647_Marking_thermometers.jpg/500px-PSM_V39_D647_Marking_thermometers.jpg)
Fig. 7.—Marking Thermometers.
liquid. The hydrometer is simply such a float as this. It is made in different forms and styles, according to the use for which it is intended; but in all cases it is essentially a cylinder or bulb of