217. Precautions to be taken in the use of hydrometers and thermometers.
- Glass hydrometer stems should be lifted from the wooden box by the large bulb and not by the narrow stem. If the bulb is at all tightly jammed in the box and the stem is used to try to raise it, there is such risk of breakage.When it sticks, it should be taken out of use if for any reason they fall to float vertically. The presence of mercury in the upper bulb or hollow shaft does not make the readings inaccurate as long as the stem floats truly.Thermometers should be carefully examined from time to time to see that the mercury column has not become separated in sections and that no portion of it has lodged in the wider part at the top of the stem. Should this happen, the thermometer should be securely grasped by the stem towards the top end and then sharply jerked downwards. If this fails, the bulb may be gently heated until the mercury again forms one unbroken.
