When at rest, the plunger or vane of a dipper break may  be arrested at the end of its dip—that is, immersed in the  mercury—and if the current were suddenly switched on, it would  recovery much less unpleasant. Methylated spirit is com-  monly used, but it is better to use rectified spirit; for,  though initially more expensive, it requires changing much  less frequently, and, further, has less corrosive action on the  metal parts. The level of the alcoholic liquid must be kept  well above the highest point of travel of the dipper, or other-  wise the liquid may ignite, causing an alarming, if not  dangerous, explosion.

To clean, the emulsified liquids should be allowed to settle,  the clearer spirit settling out on top decanted off, and the  mercury heated gently in a retort with condenser attached,  pass direct to the primary of the coil, and possibly do much  damage. Hence, it is important to see always that the motor  is in action before the supply current is switched on. This is  secured in our installation, as described later, by a special  form of switch.

The churning action of the break gradually causes some  degree of emulsification of the mercury and the covering  fluid (or dielectric); thus these materials require periodical  renewal. More or less of the mercury can always be recovered,  and, with this in view, alcohol will be found to be the prefer-  able material for a dielectric, as making the process of  whereby the remaining spirit is vaporised and the mercury  recovered for further use.

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