piston in inches by the speed of the piston in feet per minute, and divide the product by 33,000. The quotient equals the common multiplier, or the number of horsepower that each pound of effective force on the piston will drive. Then multiply the effective mean pressure, as found by diagram, by the common multiplier; the quotient is the indicated horse-power of the engine. Thus, Fig. 25—

The consumption of coals per indicator horse-power per hour is found by dividing the number of pounds of coal consumed by the product of the indicated horse-power and the time in hours. The quotient is the quantity consumed per horse-power per hour.

Suppose diagram Fig. 25 represents an engine using 34 tons per week of 58 hours, then the coal consumed per horse per hour is 3.7 lbs., or, say, 3 per horse. Thus

2240 X 3476160 lbs. of coal per week 35466 X 58

20670 divisor

Then

20670)76160(3.68 lbs. per horse-power

62010

141500

124020

174800

165360

9440

CHAPTER XIV.

SELECTION OF MACHINERY, USEFUL RULES, &c.

THE selection of the requisite machinery for any particular class of manufacture is a matter of the highest importance, and unless judiciously undertaken, an investor may find himself saddled with a lot of costly and elaborate machines ill adapted to his wants. Care should be taken that the machinery selected should combine first-class workmanship and material.

Manufacturers now generally make a speciality of one branch of engineering, and there is less difficulty than formerly in finding out who to apply to for information.

In ordering or obtaining quotations for machinery be as explicit as possible. (1.) State the exact range of work you wish to perform, and the amount of it. (2.) If you know the type and size of the machine that will suit your requirements, state them. (3.) If there is anything special in the nature of the material to be worked state it, or send a sample. (4.) State how your machinery is driven, whether from above or below, and give speed of shafting from which you propose to drive. (5.) Should there be any difficulty as regards foundation from water or other causes, name it. (6.) In the case of renewals or repairs, send the old parts, if possible; if not, an exact sketch of what is required.

As a rule our advice as to buying second-hand machinery is don't. But if you will do so, go to the expense of having it carefully examined "by one who knows" before the

new.

purchase is concluded, or you may have to pay nearly as much to have it overhauled and put into proper working order as the difference in cost between second-hand and This advice is particularly necessary with complex machines. Do not purchase old out-of-date machines because they can be had cheap, as it never pays, the quantity and quality of the output being less and the machine as a rule constantly needing repairs.

TO FIND HORSE-POWER BY MEANS OF FRICTION BRAKE.

W

T

Fig. 27.

The brake horse-power of an engine tested by the Royal Agricultural Society of England on the friction brake is obtained by multiplying the weight lifted, W., by 6.28 times the radius R of the point of suspension in feet, and by the number of revolutions made in a given number of minutes, and

dividing the sum thus arrived at by the number of minutes and 33,000.

RULE FOR CALCULATING THE POWER OF THE ROYAL AGRICULTURAL SOCIETY'S DYNANOMETER.

Rule I. For the load on brake.

Divide 33,000 by the circumferenee of the brake in feet. Multiply by the number of revolutions per minute of the brake, which will give the load in pounds for one horse-power.

Rule II. To find the horse-power of the load on brake.

Multiply the load in pounds by the number of revolutions per minute of the brake and by the circumference of the brake in feet, divide the product by 33,000.

Example I. (by Rule I.). To find the load to put on brake for 20 horse-power when the circumference of the brake 17·5 feet, and the revolutions of brake 135 per minute.

Example II. (by Rule II.). To find the horse-power when load on the brake 251.4 lbs.