The following example illustrates the method of finding the weight of any ore per square fathom in a vein. What quantity of galena will be produced per square fathom from a mineral vein 6 inches in width? One quarter of the vein consists of galena, the remainder of zinc-blende. One-twentieth must be allowed for cavities in the vein. The specific gravity of galena is 7·5, and a cubic foot of water weighs 1000 ounces; therefore a cubic foot of galena weighs 7500 ounces. The vein being 6 inches thick, there are 18 cubic feet in a square fathom. One quarter of that amount, or 4·5 cubic feet, consists of galena. The weight of galena in ounces is therefore: 7500 × 4·5 = 33,750 = 2109·375 lb. From this one-twentieth or 105·468 lb. -------------- must be deducted, leaving 2003·907 lb. or 17 cwt. 3 qr. 15 lb. as the weight of lead ore per square fathom. ESTIMATING ORE VALUES. In testing a gold mine with a view to purchase, it should be remembered that as a rule the intersections of leaders or small veins with the main ore body are usually the richest portions of the lode. This the experienced prospector knows, and generally his shafts and cuttings are made at such points. For the ordinary mining investor, when inspecting with a view to purchase, these are places to avoid if endeavouring to form a correct estimate of the value of the ore in bulk. Take samples across the lode from place to place, break down and bag personally, and mark bags. Test the rich portions separately and average, estimating quantity of both. [Illustration: PLATE VII.--CALIFORNIA PUMP. _To face p._ 171.] CALIFORNIA PUMP. Any handy man or rough bush carpenter can make a California Pump. The prospectors in the illustration (Plate VII.) are using a home-made contrivance, which is quite effective for raising water from shallow depths for “long tom,” or ground sluicing--a wooden frame-work and open wooden wheel with handle. Over the wheel is run a belt of canvas, say, six inches wide, with wood stops about a foot apart--a long sloping box, dipping into the water, up which the stopped belt travels--and you have a California Pump which, if not a highly scientific device, is at least very serviceable. HYDRAULICS. _General Data Regarding Water._ An imperial gallon of water weighs, at 62° F., 10 lbs. avoirdupois. Gallons × ·1606 = cubic feet. Cubic feet × 6·288 = number of gallons. Gallons × 277·46 = cubic inches. Cubic inches × 0·003604 = gallons. Cubic feet of water × 62·28 = number of pounds weight. Pounds of water × 0·0166 = cubic feet. Gallons of water × 0·004464 = number of tons. Tons of water × 224 = gallons of water. Cubic feet of water × 0·0278 = number of tons. Tons of water × 35·97 = cubic feet of water.