The table above gives the capacities of round cisterns or tanks. If the cistern is rectangular the number of gallons and weight of water are found by multiplying the dimensions of the cistern to get the cubical contents. For instance, for a cistern or tank 96 inches long, 72 inches wide, and 48 inches deep, the formula would be: 96 × 72 × 48 = 331,776 cubic inches.
As a gallon contains 231 cubic inches; 331,776 divided by 231 gives l,436 gallons, which multiplied by 8.33 will give the weight of water in the cistern.
For round cisterns or tanks, the rule is: Area of bottom on inside multiplied by the height, equals cubical capacity. For instance, taking the last tank or cistern in the table: Area of 24 inches (diameter) is 452.39, which multiplied by 12 inches (height) gives 5427.6 cubic inches, and this divided by 231 cubic inches in a gallon gives 23 gallons.
Supposing the tank to be 24 inches deep instead of 12 inches, the result would be, of course, twice the number of gallons.
Rule for Obtaining Contents of a Barrel in Gallons.
Take diameter at bung, then square it, double it, then add square of head diameter; multiply this sum by length of cask, and that product by .2618 which will give volume in cubic inches; this, divided by 231, will give result in gallons.
WATER METERS.
Water meters, or measurers (apparatus for the measurement of water), are constructed upon two general principles: 1, an arrangement called an “ inferential meter” made to divert a certain proportion of the water passing in the main pipe and by measuring accurately the small stream diverted, to infer, or estimate the larger quantity; 2, the positive meter; rotary piston meters are of the latter class and the form usually found in connection with steam plants. They are constructed on the positive displacement principle, and have only one working part—a hard rubber rolling piston—rendering it almost, if not entirely, exempt from liability to derangement. It measures equally well on all sized openings, whether the pressure be small or great; and its piston, being perfectly balanced, is almost frictionless in its operation.
Constructed of composition (gun-metal) and hard rubber, it is not liable to corrosion. An ingenious stuffing-box insures at all times a perfectly dry and legible dial, or the registering mechanism which is made of a combination of metals especially chosen for durability and wear, and inclosed in a case of gun-metal.