Thus, if a stone takes 5 seconds to fall to the bottom of a shaft—
5² = 25 and 25 ° 16 = 400 feet, the required depth of shaft.
DESCRIPTION OF PLAN FOR RE-USING WATER.
Where water is scarce it may be necessary to use it repeatedly. In a case of this kind in Egypt, the Arab miners have adopted an ingenious method, which is shown in [Fig. 47], and may be adapted to almost any set of conditions. At a is a sump or water-pit; b is an inclined plane on which the mineral is washed and whence the water escapes into a tank c; d is a conduit for taking the water back to a; e is a conduit or lever pump for raising the water. A certain amount of filtration could easily be managed during the passage from c to a.
Fig. 47.
COOLING COMPOUND FOR HEATED BEARINGS.
Mercurial ointment mixed with black cylinder oil and applied every quarter of an hour, or as often as expedient. The following is also recommended as a good cooling compound for heavy bearings:—Tallow 2 lb., plumbago 6 oz., sugar of lead 4 oz. Melt the tallow with gentle heat and add the other ingredients, stirring until cold.