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As to the best Boiler Feeder for your plant, pin your faith to

The Penberthy
Automatic Injector

It can be trusted to give always the same unvarying satisfactory service. Its record for handling hotter water starting at the lowest pressure, and working at highest pressure, has made it a favorite with over 350,000 engineers. Follow their example and get the best.

The Penberthy
Low Water Alarm

differs from the usual "column" type, and is in every way
better and surer. It cannot be stopped by lime or sedi-
ment, and has been proven by every test absolutely reliable.
Best and costs less.

Every engineer should have our catalog ready for instant reference. Write for it to-day,




Largest Manufacturers of Injectors in the World.



Penberthy Bulletin sent free for three months.

Mention The Technical World.

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0, Off on Catalogue Prices

"Hereafter we will give to the public direct in fall all teachers' and dealers' discounts on violins, guitars, mandolins, and other stringed instruments. Our standard Lewis Orchestra No. 1 violin {worth easily $25 to $30 among dealers; listed in our catalogue for years at $21; now $10.50 net direct to you). The famous Lewis Stradivarius model $65 violin for £32.50. Other values for from $.'* 50 to $125 and upward. We i are the largest and oldest exclusive stringed 'instrument house in the U. S., and import direct from our own worKshops in Eisleben, Germany, and Padua. Italy. Ten days' free trial of our instrument. Write for catalogue.


Dept. T. 220 Wabash Avenue. Chicago, 111. OUR SPECIALTY: Strings for the professional trade.

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Answer: Your question cannot be given an absolute answer, for the reason that the M. E. P. depends on other factors than those which you have given. In other words, it would be necessary to know the cut-off, the back pressure, and type of engine. Making certain assumptions, we can give you an approximate answer. If the cut-off is %, then the ratio of expansion is 4, neglecting clearance. Assuming the back pressure to be 3 pounds gauge, then the M. E. P. can be found by the formula

M. E. P. = P1+h>pR'ogR_/,

in which

P = Absolute initial pressure.

R = Ratio of expansion.

/> = Back pressure (absolute).

Since the gauge pressure is 80 pounds, P is 80 + 14.7 (= 94.7) pounds; R we have assumed to be 4; and p is 3 + 14.7 (= 17.7). Substituting in the formula, we have:

M. E. P. = 94.7 l+J-386? _ 177 4

= 56.5—17.7 = 38.8 pounds.

We have made no allowances for losses due to compression, clearance, condensation, wire drawing, etc. To allow for these in a plain slide-valve engine, it is customary to multiply this theoretical M. E. P. by the factor .8, which will give us for the probable M. E. P., 38.8 x .8 (= 31.04) pounds.

In the formula used above, you will find the term "hyp. log. R.'' We are to substitute for this term the hyperbolic logarithm, or, as it is sometimes called, the Napierian logarithm of the factor R. These logarithms will be found in almost any engineer's handbook.

Exhausting Under Water

Question: Is it possible for two-cycle gas engines to exhaust under water without seriously reducing the H. P. of the engines?— B. O.

Answer: This is frequently done without loss of H. P. by extending the terminal under water, with a small vent above the water. The vent prevents the water from drawing back to the muffler when the motor stops.

Mention The Technical World.

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C. Model "H." Capacity four passengers. Speed up to twenty-
five miles an hour. $850. Equipped with tools, oilers, pump,
repair kit, brass oil side lamps and brass horn.

C In this model the speed is regulated by the trottle attached to
the steering wheel, requiring only one hand to steer and control.
The ignition is timed automatically by a governor in exact require-
ment to the speed of the engine. Brakes both on transmission and
rear wheels. Power sufficient for grades up to forty per cent.

C Made in our own factory where the facilities are so complete that they
involve the making of bolts and nuts even. These exactly fit the spanner
wrenches which go with our vehicles.

C. The tonneau of Model " H" can be readily removed and the
vehicle converted into a run-about, Model "G", and at slight
expense delivery wagon top can be added. C. Send for THE
RAMBLERj cTWAGAZINE and other printed matter.

Thomas B. Jeffery" C& Company"


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Preparation for College


Instruction under the direction of the regular teachers in a resident engineering college.

Lessons prepared especially for home study by teachers of acknowledged standing.

The full College Preparatory Course corers the entrance requirements of such a college as ARMOUR INSTITUTE OF TECHNOLOG Y, and students satisfactorily completing this course are admitted to the college of engineering of that institution without further examination in the subjects taken.

An unusual opportunity toryoung men of United means to prepare for entrance to an engineering college without leaving home or interfering with their regular work

CHILDREN AT HOME as long as pos-
sible before sending them to college will
And these courses of great value. There
is no breaking of home ties, and the
student not only has many of the ad-
vantages of a private tutor but also the
sympathy and encouragement of his

This is an excellent opportunity for tcaehers and others to take up engineering studies in their own homes and at their own convenience under the guidance of resident school teachers.

In addition to the College Preparatory Course instruction is also offered in

Mathematics (Arithmetic,Algebra,Geom-
etry and Trigonometry), Electrical,
Mechanical, Steam, Sanitary and Civil
Engineering; Architecture, Mechanical
Drawing, Telegraphy, Telephony and
the manufacture of Textiles (Spinning,
Weaving and Knitting).

200 page illustrated Bulletin, giving full information as to courses, teachers, methods of study, etc., may be had upon request.

American School of Correspondence


Armour Institute of Technology


i Mention The Technical World. Dec. ssa

Mention The T


Current of Open and Closed Motor

Question: Upon the name plate of a G. E 500-volt direct-current compound-wound motor is the following:

"Open 10 H. P 17 amperes.

Closed 5/2 H. P 10 amperes."

Will you kindly explain the meaning of this?— H. C. J.

Answer: This doubtless refers to the condition of the machine running in the first place as an open motor, and in the second as an enclosed motor. It will be noticed that a current of 17 amperes is allowed in the first case, or when the machine is running as an open motor; and a current of only 10 amperes, when the machine is running as a closed motor. This discrepancy is, of course, due to the difference in ventilation, the open motor being much better ventilated than the enclosed.

Domestic Heating System

Question: I wish to put a heating system in my house. Kindly give me some rules by which 1 can determine the size of pipe necessary, the dimensions of radiators, etc.—H. B,

Ansxvcr: Your inquiry is entirely too indefinite, since there are so many variable factors connected with any heating system, and you have omitted to state the exact conditions. The principal points to be considered are:—First, the system itself, t. c, whether a furnace, steam, or hot water is to be used. Second, the location and exposure. Third, the material of which the building is constructed, and the purpose for which it is to be used. The following general rules can be used for rough calculation; but when it comes to actually laying out the plant, more exact rules which necessitate the knowledge of the conditions outlined above, should be used.

Using steam, one square foot of direct radiation will supply from 60 to 80 cubic feet in ordinary dwellings. If indirect radiation is used, these figures would be from 40 to 50 cubic feet. If hot water of high temperature is used, one square foot of radiation will take care of 50 to 70 cubic feet: and if low-temperature hot water is used, these figures should be from 30 to 50.

rchnical World.

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