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There are several rules for calculating the weight. For many reasons it is best to use a rule which involves the dimensions of the cylinder and the speed of the engine. Indeed, no satisfactory results could be obtained by figuring on the H. P. alone. A satisfactory formula is :

_C * * * እ

W= D2 X N in which C is a constant that varies for different conditions (for ordinary work it is about 700,000); d is the diameter of the cylinder in inches; b is the length of stroke in inches ; D is the diameter of fly wheel in feet; N is the number of revolutions per minute ; and W is the weight of the rim in pounds.

Knowing the diameter of the fly wheel, the width of the face and thickness can be determined, since the weight is considered as being in the rim. If b equals the width of the face in inches, the thickness of rim in inches, and d the diameter of fly wheel in inches, we then have: W (total weight) = .2607 (weight of 1 cubic inch of cast iron) X X t X 7 d = b X 7.819 d. Either the breadth or the thickness must be assumed, and then the other dimension determined from the formula.

Grove Gas Battery Question: Please describe the Grove Gas Battery. What voltage will a single cell of this battery produce?-G. JI. D.

Answer: In the battery that bears his name, Grove immersed two platinum plates covered with films of different gases in a dilute solution of sulphuric acid. Between the platinized platinum plates charged with different gases and a platinum electrode saturated with hydrogen, he obtained the following E. M. F.'s: VOLT

VOLT Chlorine ....... 0.63 Cyanogen ...... 0.42 Bromine .......

0.56 Carbon dioxide.. 0.42 Oxygen ........ 0.48 Nitric oxide .... 0.41 Iodine ......... 0.48 Air ............ 0.41 Nitrous oxide... 0.43 Pure platinum.. 0.40

This battery is interesting from a scientific rather than a commercial standpoint.

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A SCHOOL W IT H I N IT SE L'E THERE are XIX chapters of subjects, carrying you from the fundamental principles of electricity on through the

various branches to a point where the careful student comprehends the complete designing, care and operation

of a dynamo or motor. Each subject is carefully written and to the point. After a student studies a subject, he is questioned on that subject in such a manner as to bring clearly to his mind the points he needs to know regarding same. A DICTIONARY in back of book will enable him to learn the meaning of any electrical word, term or phrase used in this book, as well as hundreds of others in common use. All required tables necessary in the study are in it.


$2.00 per Copy-Third Edition 11,000 Copies Sold The offer we make of refunding money if book is

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Star vs. Delta Connection Question: Please explain the advantage of the Star connection over the Delta connection in the three-phase generator for long-distance transmission.-A.

Answer: In the case of the Star connection, the voltage between the mains is V3 times as great as that over the coils, while the current in each main is the same as that in the corresponding coil.

In the case of the Delta connection, the voltage between the mains is the same as that over the coils, while the current is V3 times as great in the mains as in the coils. On this account, the Star connection is more suitable for long-distance transmission than the Delta.


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Horse-Power of Triple-Expansion


Question: Please let me know through The Castings, Materials and Blue Prints, complete, $16.50. TECHNICAL WORLD, the formula for figuring Horizontal and Upright Types. Send for

the H. P. of a triple-expansion engine by conCircular 7.

densing the M. E. P. of the cylinders to the PARSELL @ WEED

low pressure; sizes of cylinders, 28 inches, 48 129-131 West 31st St. NEW YORK CITY

inches, and 72 inches; stroke, 42 inches; vacuum, 26 inches ; piston travel, 200 feet per minute; boiler pressure by gauge, 160 pounds. -W. J. O.

Answer: In reducing all the pressures

to the area of the low-pressure cylinder, ST. LOUIS PHILADELPHIA BALTIMORE

the same general formula as for a simple Engineering Instruments,

engine can be used ; that is :
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· H. P. – P x L X A XN


in which P is the sum of the total M.
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E. P.'s referred to the low-pressure cylAre the Best." inder; L, the length of stroke in feet; Second Hand Transits, Levels bought, sold A, the area of the low-pressure cylinder or exchanged. Repairing neatly done.

in square inches; and N, the number of Send for Illustrated Catalogue,

strokes per minute. To reduce the M. Ghe World's Headquarters for

E. P. of each cylinder to the correspond

ing pressure on the low cylinder, you Electric Novelties and Supplies

must multiply the M. E. P. of the cylIf It's Electric We Have It. We Undersell All. inder under consideration by the ratio Fan Motor and Bat:ery ....'2 to $10.00

of its volume to the volume of the low-
Battery Table Lamp........ 3.00
Battery Hanging Lamp... 10.00 pressure cylinder. If, as is usually the
Telephone, complete......

Electric Door Bells ......

1.00 case, the stroke is the same in all cylElectric Carriage Lamps.. 5.00 Electric Lanterns...

3.00 inders, then the ratio of the volumes $8.00 Medical Batteries........ 3.95 $12.00 Belt, with Suspensory..

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2.50 pressure cylinder is:
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CONSULTING DEPARTMENT-(Concluded) Multiplying the M. E. P. of the intermediate cylinder by 4/9, we would have the pressure referred to the low cylinder.

Similarly, the pressure on the high can be determined; and if we add the M. E. P. of the high and intermediate (referred to the low) to the M. E. P. of the low itself, we have the total M. E. P., or the value of P in the formula. Of course the M. E. P. mentioned above cannot be determined accurately without the aid of the indicator diagram.

If the piston speed in feet per minute is given, then the terms L and N in the formula can be omitted, and the piston speed substituted.

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Cement for Leather Question: Give formula for quick - setting cement for leather belts, that oil will not affect.-A. W. N.

Answer: Take 16 parts gutta-percha, 4 India rubber, 2 pitch, I shellac, 2 linseed oil. Cut small, melt together, and mix well.

Bignall @ Keller Mfg. Co. I Leclaire, Edwardsville, Illinois

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Resistance of Ground Question: Please give me formula for the resistance of a ground by the voltmeter method.-F. W. W.

Answer: This can be found by using a Weston voltmeter as follows: Connect one side of the circuit to one bindingpost of the voltmeter, and connect a water pipe to the other binding-post of the voltmeter. If now there is any deflection, we know that there is a ground on the opposite side of the circuit from that to which the voltmeter is connected. The resistance of this ground may be found by the formula :

R=r( -1), in which R equals the resistance of the ground leak required; r equals the resistance of the voltmeter; V equals voltage between the positive and negative sides of the line; and y equals the reading of the instrument.

Fred T. Hodgson, Editor

A PRACTICAL Building Monthly Journal.

Each issue contains a manila supplement 24 x 36 showing the complete plans of a build

ing drawn to scale with full details. A detailed estimate accompanies it. The reading pages contain live matter on important subjects such as Hollow Block Construction, Styles of Architecture, Builders' Tools, etc., etc.

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