Cisterns and Tanks.-The pressure of water is equal in all directions, and water will rise to the same level in all parts communicating with a vessel containing it, whatever be their shape and form. The centre of pressure of a rectangle is at two-thirds the depth from the top. The centre of pressure of a triangle whose base is horizontal, and upon the water line, is at one-half of the depth. The centre of pressure of a triangle whose summit is at the water-line, the base being horizontal and at the lower level, is at three-fourths of the depth. The centre of pressure of the water in a cistern is at two-thirds of the depth of the water, measured from the surface of the water. The mean pressure of the water in a cistern is at one-half of the depth of the water. The maximum pressure of water in lbs. on each of the sides and ends of a cistern is at the point of the centre of pressure, and it is = Depth of the water in feet × × 62:42 lbs. × the area in square feet of the wetted surface of the side or end of a cistern. The mean pressure of water in lbs. on each of the sides and ends of a cistern is equal to one-half the pressure due to full depth, and it is Depth of water in feet × 5 × 62:42 lbs. × the area in square feet of the wetted surface of the side or end of a cistern. = = = = = the length The pressure of water in lbs. on the bottom of a cistern is in feet the width in feet x the depth in feet × 62:42 lbs. Take, for instance, a cistern 8 feet long, 5 feet wide, and 4 feet deep. full of water. Then the maximum pressure, or that at the point of the centre of pressure, is 4 feet deep of water x x 62:42 lbs. 187.26 lbs. pressure per square foot of the surface of each of the sides and ends of the cistern. The total pressure on each side of the cistern, at the point of the centre of pressure, is 8 feet x 4 feet × 187.26 lbs. 6,742 lbs. The total pressure on each end of the cistern, at the point of the centre of pressure, is 5 feet x 4 feet x 187.26 lbs. 4,224 lbs. The strength of the material of a cistern is governed by the mean pressure. The mean pressure on each of the sides and ends of this cistern is = 4'5 feet deep of water ÷ 2 × 62:42 lbs. 1405 lbs. per square foot of surface. The total pressure on each side of the cistern is 8 feet x 4 feet × 140'5 lbs. = 5,058 lbs., and that on each end of the cistern is 140'5 lbs. 8 feet x 5 feet × 4 feet × 62°42 lbs. = = = = = 5 feet × 4 feet × 3,162 lbs. The pressure on the bottom of the cistern is = 11,236 lbs. Table 173.-CONTENTS OF CYLINDRICAL CISTERNS-STOCK SIZES. Table 174.-GALVANIZED IRON CISTERNS-STOCK SIZES. Pumping Water.-Rules for pumps are given at pages 90-97. The following additional data may be useful:-Water is generally considered to be incompressible, but under a pressure of 65,000 lbs. per square inch, it is compressed 10 per cent., and alcohol more than 15 per cent. The weight of one cubic inch of pure or fresh water, at a temperature of 65° Fahr. is 03607 pound, and cubic inches multiplied by 003607 = gallons; and gallons multiplied by 16045 = cubic feet. = The capacity of a cylinder 1 inch diameter and 1 inch long is = 1 inch diameter x 7854 x 1 inch long 7854 cubic inch; and 7854 cubic inch x 003607002832 gallon, and also=002832 x 10='02832 pound; and 002832 gallon x 16045 0004543 cubic foot. = The theoretical quantity of water delivered by a pump may be found with the above data by the following rules : Let D= the diameter in inches of the pump ram, or of the barrel of the pump, if it be fitted with a water-piston; S = the length of stroke of the pump in inches; N = the number of strokes per minute during which water is admitted to the pump. = = The discharge of a pump in cubic inches per minute = D2 × 7854 × S× N. The discharge of a pump in cubic feet per minute = D2 x S x '0004543 × N. The discharge of a pump in pounds per minute D2 x S x '02832 x N. The discharge of a pump in gallons per minute D2 x S x ou2832 x N. In pumping sea-water multiply the discharge found by these rules by ro26. Example Required the quantity of water in gallons discharged by a pump having a ram 4 inches diameter, and 6 inches stroke; water being admitted to the pump during 100 strokes per minute. Then 45 inches diameter x 4'5 inches x 6 inches stroke x 002832 × = 100 strokes per minute 34'4 gallons of water discharged per minute, and 34°4 × 60 2,064 gallons per hour. = = These rules apply to both single-acting and double-acting pumps. Flow of Water in Pipes.-Rules for the discharge of water from pipes are given at pages 89 and 108. The following are also useful rules:— The velocity of water in feet per minute necessary for the discharge of a given quantity of water may be found by this rule :— Cubic feet of water discharged per minute × 144. Sectional area of the pipe in square inches. The following are common velocities for the flow of water in pipes for water-supply: Diameter of pipe in inches per second 4 6 12 18 24 36 48 The sectional area of a pipe in square inches necessary for a given quantity and velocity of water may be found by this rule :Cubic feet of water discharged per minute × 144. Velocity of the water in feet per minute. Tarea Tarea in square inches ÷ 7854). The theoretical indicated horse-power required to raise water may be found by these rules:— Pounds of water raised per minute x height of lift in feet 33,000. Cubic feet of water raised per minute x height of lift in feet 529. In practice it is necessary to make an addition to the theoretical power of from 25 to 50 per cent. to allow for the friction in working the pump. The head required to produce a given velocity of water in a pipe may be found by the following rule from "Engineering," which is based on the fact that in the majority of cases the velocity of flow in a pipe is from 2 feet to 4 feet per second, the average being 3 feet per second. The head required to maintain a velocity of 3 feet per second through a length of clean cast-iron pipe is : Head in feet 25 × diameter of pipe in inches. The discharge in cubic feet per minute is very nearly equal to the square of the diameter of the pipe in inches, the error being under 2 per cent. in excess. For a velocity of 1 foot per second less than 3 feet per second, the head must be reduced one-half, and by a proportionate amount for intermediate cases. For a velocity of 1 foot per second more than 3 feet per second, the head must be increased by 7 times that required for a velocity of 3 feet per second, and that required for intermediate cases may be determined by adding a proportionate amount for that required for the I foot per second increase in velocity. = = Discharge of Sewage.—A gallon of water, and also of sewage, weighs 10 lbs.: one cubic foot weighs 62:42 lbs. = 6 gallons: one cwt. is 18 cubic feet 112 gallons. One inch in depth of sewage over an acre of land is equivalent to 101 tons, or 22,600 gallons. The average weight of the solid and fluid excreta of a human being is 24 lbs. per day. The urine of 100,000 persons weighs 234,380 lbs., and the fœces of 100.000 persons weighs 15,620 lbs., the fœces, or solid portion, being to the fluid. or urine, as I to 16. For corrosion of metal by sewage, see page 340. The diameter of a sewer may be found by the following formula from the "Engineer":-Multiply the quantity of water in cubic feet consumed per head of the inhabitants per day by the number of the inhabitants. This will give the total sewer discharge for 24 hours. Assume that onehalf of this quantity will pass into the sewers in six hours, and calculate the number of cubic feet per second. To this must be added the rainfall. Assume that rain falls to a depth of inch in 24 hours over the whole area of the district, and calculate the number of cubic feet per second of rainfall. Add this to the volume of sewage in cubic feet per second, and the product is the total volume of liquid flowing into the sewer. Assume any size of sewer, say 2 feet in diameter. Calculate by the following formula the velocity of discharge, with the inclination of 1 in 630, or 8.38 feet per mile. = = V = '92 √2fhy. In which V= the velocity in feet per second; ƒ the fall in feet per mile 8.38; hy the hydraulic mean depth = the area of the sewer divided by its circumference, which is 5 feet for a sewer 2 feet diameter. Multiply the velocity obtained by this formula by the area of the sewer, = 3141 square feet in this case, and if the product is more or less than the total volume of sewage and rainfall, a smaller or larger size of sewer must be assumed and the calculation repeated. Mr. R. Hering gives the following rule for the flow of sewage : In which V= the velocity in feet per second; the hydraulic radius, the slope of the fluid surface. r= This formula is applicable to all varieties of sewer with a maximum error in this class of work of 5 per cent., which is always on the safe side. If greater accuracy is required the following formula may be used: V = (A r √s) ÷ (B + √r). In which A and B are constants depending on the character of the surface of the sewers, and their values for different cases are as follows: Surface of bad brickwork with washed-out joints. QUALITIES OF METALS. Gold of fine or pure quality is nearly as soft as lead. To enable it to resist wear, it is hardened by alloying with copper and silver. The fineness of gold is denoted by the number of carats present in 24 carats of the alloy, pure gold being 24 carats fine; standard or sovereign gold is 22 carats fine, and is a mixture of 22 parts gold and 2 parts copper. A new sovereign weighs 123°27447 grains, or a little more than 123 grains, and when its weight is reduced by wear to under 122 grains it is not a legal tender. A new half-sovereign weighs 61.63723 grains, and when its weight is reduced by wear to under 61125 grains, it is not a legal tender, After a sovereign has been in circulation for 20 years, its weight will have been reduced by wear to a little below the minimum legal weight. The gold coinage of this country weighs about 800 tons. The gold used for the best class of jewellery is 18 carats fine, and is a mixture of 18 parts gold and 6 parts copper. The gold used for common jewellery is 9 carats fine and is a mixture of 9 parts gold and 15 parts copper. Jewellers test gold with nitric acid, which leaves a stain on metal which is much alloyed, the colour of the stain varying according to the quality of the metal. Nitric acid does not affect 18 carat gold, but produces a dark stain on 9 carat gold, and a green stain upon the metal when a large proportion of copper, brass, or German silver is present. Gold dissolves in aqua regia or a mixture of one part nitric acid and four parts hydrochloric acid. Silver of fine or pure quality is soft and ductile; its power of conducting electricity and heat is superior to all other metals. Standard silver used for coins, is a mixture of 92 parts silver and 7 parts copper, 1 lb. of which contains 11 oz. 2 dwts. silver and 18 dwts. copper. The fineness of silver is denoted by the number of dwts. it is better or worse in quality than standard silver. Nitric acid produces a black mark on fine silver, and a green mark on silver which is much alloyed. Copper being more malleable than ductile, is more suitable for being hammere I and rolled into plates, than being drawn into wire; its malleability and ductility depend greatly upon its purity. Copper, during the process of being hammered, rolled, or drawn into wire, becomes hard, stiff, and liable to crack, and requires to be frequently annealed to restore it to its normal quality; when these processes are carefully carried out, the strength of copper is thereby considerably increased. Bean-shot copper is obtained by pouring melted copper into hot water, and feathered-shot copper by pouring melted copper into cold water. The bronze coinage of this country and of France is a mixture of 95 parts copper, 4 parts tin, and I part zinc. One farthing weighs oz., I halfpenny oz, and 1 penny oz. Tin possesses very little tenacity, but is very malleable, and may be beaten and rolled into thin leaves of tin-foil of the one-thousandth part of an inch in thickness; when quickly bent tin gives a creaking sound. Tin is not much affected by weak acids, or by exposure to the air. Tin-plate is sheet-iron coated with tin. Tin-salt is obtained by dissolving tin in |