Find the load, by multiplying the area of the safety-vaive in square inches, by the pressure of the steam in lbs. per square inch; then multiply the load by the diameter of the coil, from centre to centre of the steel; divide the quotient by the constant number 3. for round steel, or by the constant number 4.29 for square steel, and the cube root of the quotient will give the size of steel in sixteenths of an inch, that is, the diameter when round, and the side of the square when square.

To find the compression or extension of one coil in inches:— Cube the diameter in inches of the coil (from centre to centre of the steel), then multiply by the load in lbs., and divide the product by the product of the fourth power of the diameter (or side of square if square) of the steel in sixteenths of an inch, multiplied by the constant number 22 for round steel, and 30 for square steel.

To find the pitch of a spiral spring:-The distance between neighbouring coils should be equal to twice the compression (or extension as the case may be), found by the last rule, and the pitch will be twice the compression added to the diameter of the steel when round, or the side of the square when square.

To find the number of coils :-Divide the initial compression of spring (or 4 inches for all sizes) by the amount of compression, or extension of one coil (found by the above rule), which will give the effective number of coils.

To find the length of spring, multiply the number of coils found by last rule by the pitch of spiral, and add two more coils, to allow for the two end coils serving as bases for the spring.

The above rules are for valves loaded with direct springs, but the same rules apply to springs acting at the end of levers, in which case the lift of the end of the lever where the spring is attached, must be taken instead of the lift of the valve.

Laminated Springs for Locomotive Engines, railway carriages and waggons, and conveyances.-The thickness of steel plate for springs under 3 to 4 feet span, should not exceed inch in the smaller, and from to inch in the larger sizes; for larger spans the thickness is generally inch, with the two top plates inch thick. about inch for railway waggons, 1inch for horse boxes, and from 1 The following are Mr. D. K. Clark's rules for laminated or plate springs.

The deflection per ton of load, is to 1 inch for locomotive engines, to 2 inches for railway carriages.

Let D= the deflection in sixteenths of an inch per ton load.

S = the span of the spring in inches when loaded.

ỏ = the breadth of the spring plate in inches, considered uniform.

n

= the thickness of plates in sixteenths of an inch.

=

the number of plates.

W the working strength of spring in tons, or safe load.

and necessary to a given elastic flexure, span, and size of plates =

CHIMNEYS FOR FACTORY STEAM BOILERS.

The source of power for the draught of a chimney, is the difference in weight of a vertical column of cool air outside the chimney, compared with that of a vertical column of the heated gases inside the chimney. These two columns of air being of unequal weight, motion ensues. The best draught takes place, when the temperature of the gases inside the chimney is at 552°, which weighs only one-half the weight of the air outside the chimney when at 62°. A quantity of heat is absorbed in producing draught, but only about one-fourth the quantity of the heat is required to raise 1 lb. of air one degree, which is required to raise 1 lb. of water one degree, and the heat carried off by the gases may be found thus Multiply the weight of air per lb. of coal, by the difference in temperature between the gases in the chimney and the external air, and multiply the product by 238. The quantity of air required is 24 lbs. for each lb. of fuel. The usual rate of combustion is from 14 to 26 lbs. of coal per square foot of grate-area per hour in Cornish and Lancashire boilers.

Proportions of Brick Chimneys-For an ordinary factory chimney, say, one for a good-sized cotton factory, the thickness of brickwork is 9 inches at the top; 14 inches at a distance of one-fourth the height from the top; 18 inches at one-half the height; 23 inches at a distance of threefourths the height from the top; and 28 inches at the base.

To find the area in square feet at the top of a chimney for a given boiler Rule, multiply the area of the fire-grate surface in square feet by So, and divide the product by the square root of the height of the chimney in feet.

To find the maximum horse-power of a chimney, when the inside area at the top, and the height, are given, divide the area in square inches by 70, and multiply the result by the square root of the height in feet. This will give the maximum horse-power, but a chimney should always be made about one-third larger than necessary, to allow for contingencies.

Flues. The horse-power of a chimney reduces with the length of flue. The power with longer flues than 50 feet, may be found by

Table 44.-MAXIMUM HORSE-POWER OF FACTORY CHIMNEYS, WITH FLUES 50 FEET LONG IN CIRCUIT FROM THE
FURNACE TO THE BOTTOM OF THE CHIMNEY.

Round. Square. Round Square. Round. Squire Round. Square. Round. Square. Round. Square. Round. Square Round. Square.

the furnace to the chimney bottom. by 7 for flues of 200 feet, and by 6 for flues of 500 feet in length, from multiplying the horse-power in the following table by 8 for flues 100 feet,

The Height of Factory Chimneys in towns and populous districts should not be less than 90 feet.

A Lightning Conductor consisting of a inch copper wire-rope should be fixed, with fastenings spaced 6
feet apart, on the outside of every Factory Chimney. Insulators should not be used. Height of point above the
Chimney Top to the inside Diameter of the Chimney. Earth connection, not less than 7 yards; the wire-
strands should be unwound and spread out so as to expose as much surface to the soil as possible, which
should be permanently damp; or the wire-rope may terminate in a water pipe or well

378

484 403

562

458

587 488

546

THE PREVENTION OF SCALE IN STEAM BOILERS.

Hardness of Water is caused by the water coming in contact with various mineral substances, as it passes over or through the ground, and which it partially dissolves and holds in solution. These substances are chiefly sulphate of lime, bicarbonate of lime, and carbonate of magnesia. These, as well as various other impurities, are contained more or less in all river, lake, and well water. The action of heat in a boiler makes these substances insoluble, and causes their deposit on the boiler-plates in the form of scale, which, being a non-conducting material, retards the transmission of heat from the iron to the water, and also renders the plates liable to be burnt, by preventing the water from coming in contact with the plates. The loss of fuel caused by incrustation has been observed to be about 15 per cent. for every inch of thickness of scale. For softening water and preventing incrustation, pure caustic soda has been found to be the most effective; its strength should be 98 per cent., that is, containing only 2 per cent. impurities. Some caustic soda has only 60 per cent. strength, and contains common salts and sulphur salts, which injure the boiler plates. The pure caustic soda in powder should be dissolved in water, and introduced continually with the feedwater, by connecting the suction-pipe of the pump with the vessel containing the composition. The proper amount is, for very hard water, 1 oz. to every 5 gallons of water, and for water of medium hardness 1 oz. for every 10 gallons, and for fairly good water 1 oz. for every 15 gallons. In using caustic soda, the boiler should be frequently blown off.

Soda-ash is sometimes used, but it is not nearly so effective as pure caustic soda; besides, soda-ash often contains impurities which injure the plates.

Proportions of Fire-Bars.-Fire-bars should be as short as convenient; thin bars keep cooler, stand the fire better, and do not twist so much as thick ones. The dimensions for all lengths of bars (except in the middle, which is given below) are :—

Thickness at the top inch; thickness at the bottom = inch; the sides to be parallel at the top to a depth of about inch, and then to be tapered downwards; ends and centre rib 1 inches thick, so as to leave an air space of inch; ends 1 inches deep x 1 inches long.

THE CARE OF STEAM BOILERS.

The following is a copy of a sheet of instructions to boiler attendants, issued to their clients by the MANCHESTER STEAM USERS' ASSOCIATION.

INSTRUCTIONS TO BOILER ATTENDANTS.

Getting up Steam.-Warm the boiler gradually. Do not get up steam from cold water in less than six hours. If possible, light the fires overnight.

Nothing turns a new boiler into an old one sooner than getting up steam too quickly. It hogs the furnace tubes, leads to grooving, strains the end plates, and sometimes rips the ring-seams of rivets at the bottom of the shell.

Firing, Fire regularly. After firing, open the ventilating grid in the door for a minute or so. Keep the bars covered right up to the bridge. Keep as thick a fire as the quality of coal will allow. Do not rouse the fires with a rake. Should the coal cake together, run a slicer in on the top of the bars and gently break up the burning mass.

It has been found by repeated trials, that, under ordinarily fair conditions, no smoke need be made with careful hand-firing.

Cleaning Fires and Slacking Ashes.-Clean the fires as often as the clinker renders it necessary. Do not slack the clinkers and ashes on the flooring plates in front of the boiler, but draw them directly into an iron barrow and wheel them away.

Slacking ashes on the flooring plates corrodes the front of the boiler at the flat end plate, and also at the bottom of the shell where resting on the front cross wall.

Feed-Water Supply.-Set the feed-valve so as to give a constant supply, and keep the water up to the height indicated by the water-level pointer.

There is no economy in keeping a great depth of water over the furnace crowns, whilst, at the same time, the steam-space is reduced thereby, and the boiler is rendered more liable to prime. Nor is there any economy in keeping a very little water over the furnace-crowns, whilst the furnaces are thereby rendered more liable to be laid bare.

Glass Water-Gauges and Floats.-Blow through the test-tap at the bottom of the gauge hourly, as well as through the tap in the bottom neck, and the tap in the top neck twice daily. These taps should be blown through more frequently when the water is sedimentary, and whenever the movement of the water in the glass is at all sluggish. Should either of the thoroughfares become choked, clean them out with a wire. Work the floats up and down by hand three or four times a day to see that they are quite