The litre is the unit of liquid measure in the metric system. The litre is 1 cubic decimeter. It is nearly equal to 1 quart. More accurately, 1 litre equals .26418 gallon, or 61.027 cubic inches.

The Centigrade Thermometer.

On the centigrade thermometer the freezing point of water is 0°, and the boiling point of water at atmospheric pressure, 14.7 pounds, is 100°.

To reduce centigrade temperatures to Fahrenheit, take % of the centigrade reading and add 32.

To reduce Fahrenheit temperatures to centigrade, subtract 32 from the Fahrenheit reading and take % of the remainder.

QUESTIONS AND ANSWERS.

Rule for Calculating Heating Surface of a Tubular Boiler.

Q. Can you give me a rule for calculating heating surface of a tubular boiler?

A. Multiply two-thirds of the circumference of the shell by its length in inches, multiply the number of tubes by the length of the tube in inches and by its circumference. Add to the sum of these products twothirds of the area in square inches of the two heads or tube sheets. From this sum subtract twice the area of all the tubes, and divide the remainder by 144. This gives the heating surface in square feet.

To Find the Safe Working and Bursting Pressure of Boilers.

Q. Can you give me a formula to figure the safe working pressure and the bursting pressure of the horizontal boiler where the pitch of the rivet is figured?

A. From the pitch of the rivets subtract the diameter of the rivet hole, and divide this remainder by the pitch of the rivets. This gives the percentage of solid plate in the seam.

Multiply the tensile strength of the solid plate by the thickness of the plate, and this product by the percentage of solid plate.

Divide this result by one-half the diameter of the boiler in inches, and the quotient will be the bursting pressure in pounds per square inch.

Divide this by the factor of safety (4, 4.5 or 5), and the result is the maximum safe working pressure.

To Find the Horse-power Constant.

Q. How would you figure the H. P. constant of an engine, giving the diameter of the cylinder, the length of the stroke and the number of r. p. m.

A. The horse-power of an engine is calculated

from the formula: H. P.

=

PLAN

33,000

when P is the

average or mean pressure throughout the stroke, in pounds per square inch. This average pressure must be determined from the indicator card. L is the length of the stroke in feet; A is the area of the piston in square inches; N is the number of strokes per minute.

Q. How would you equalize clearance if the piston is keyed to the crosshead?

A. If the piston rod is rigidly fastened to the crosshead, clearance may be equalized within certain limits by adjusting the wedges which hold the wrist-pin brasses in place. It may be necessary to put in new wedges in order to get the desired adjustment. The effect of this adjustment will be to lengthen or shorten the connecting rod, and since the length of the crank is fixed, and the position of the crank shaft is fixed, the head end clearance will be increased by shortening the connecting rod, while the crank-end clearance will be decreased. Lengthening the connecting rod will have the opposite effect on the clearance.

Q. Why will not a water glass show the true level of the water in the boiler?

A. A water glass may not show the true level of water in the boiler if one or both the connections to the glass become stopped, or if there is a leak in the glass at either top or bottom. A leak at the top makes the water in the glass stand too high; a leak at the bottom makes it stand too low.