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SCIENCE AND INVENTION, (Concluded) This is ensured by using an achromatic lens satisfying two additional conditions: —the focal distance, on the one hand, is fairly identical with that of the photo

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ditions as to apparent size, shadows, and THE NEW YEAR'S NUMBER OF relative distinctness as in the case of the

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a stereoscope.—DR. A. GRADEN WITZ. Mention The Technical World.

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The Engineer

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HERE'S A FEW OF THE PARTS NAMED-THERE ARE 497 IN ALL.

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Practical Books |

CONSULTING
DEPARTMENT

Just Ready-Centrifugal Fans, by J. H. Kinealy.

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M. Am. Soc. M. E. Dealing with their designing, construction and use with numerous Formulas, Illustra

Dry Battery-Electro-Gilding Bath tions and Tables. Suitable for archi

Question 1: How can I make a pocket dry tectural and engi

battery? neering drawings.

Question 2: How can I make an electro

gilding bath which gives a red color like 14E SYSTEM 8 NEW

or 18-carat gold?-). V'. C. ALPHABETS.

Answer 1: Dry cells are sold at such a low price that it does not pay an indi

vidual to spend his time in the manufactNinth Thousand.

ure of a cell. A dry battery may be By Mail 50c.

made in the following manner: Care and Handling of Electric Plants.

A jar of the desired shape is made of With very useful table, formulas and suggestions and 66 original drawings.

zinc; heavy sheet zinc should be used In limp leather ... Price $1.00

and bent into the required form, then

soldered in such a manner that it forms Spon & Chamberlain a jar. It will be found difficult to solder Publishers TECHNICAL BOOKS

zinc. All parts where it is desired the T. W., Liberty Building. NEW YORK

solder should stick should be carefully cleaned by scraping, and clean chloride of zinc used as a flux. The zinc should have a brass binding-post soldered to it. The other electrode is usually carbon,

and should have a similar binding-post Twentieth Century

fastened to it.

The contents of such cells vary. In Gassner's cell, the following mixture is

used: ANGUS SINCLAIR COMPANY

Oxide of zinc, 1 part by weight; sal-ammoniac, I part; plaster of paris, 3 parts; chlo

ride of zinc, i part; and water, 2 parts. Newly Published and is the

The cell is sealed by means of covering Best Book on

with pitch, or some similar material Railway Machinery

which will not allow salts to creep. There ever published. Contains

are many other formulæ for the contents chapterson: Elementary

· of the cell, which are used with success. lessons on first principles;

Answer 2: steam and motive power;

The following solution, workshop operations; loco

recommended for red plating, should be motive boiler construction;

used hot (at the boiling point) with a compound locomotives;

platinum wire for the anode and with valve motion; machine tools and shop appliances, and

high current density : on nine other subjects.

Phosphate of soda (crystallized), 60 parts; PROFUSELY ILLUSTRATED.

bisulphite of soda, 10 parts; cyanide of potasContains 670 pages, 6x9 inches.

sium (C. P.), I or 2 parts; neutral chloride PRICE, THREE DOLLARS

of gold, 2 parts; distilled or rain water, 1,000

parts. LOCOMOTIVE ENGINEERING

First dissolve the phosphate of soda in

800 parts of hot water. When thoroughly Department T, 136 Liberty Street

dissolved, filter the solution if not clear, NEW YORK

and allow to cool. Dissolve the gold

chloride in 100 parts water, and the biMention The Technical World.

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Locomotives

- BY

Compendium of Drawing

A COMPLETE CYCLOPEDIA
For the Library, the Shop, the Student

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900 Pages-1,000 Illustrations, Folding Plates, Etc.

SENT

FREE

FOR EXAMINATION

REGULAR price, $10.00, reduced nearly

"one-half in order to introduce the Size 8 x 10

work. No more comprehensive treatise on inches

drawing ever published. $25.00 would not

buy separate volumes covering the subjects. Practical test questions combine the advantages of a text-book with a Cyclopedia of Drawing.

OSWALD GUETH, M. E., Consulting Engineer, Technical Editor of "Cold Storage
and Ice Trade Journal," New York, says: “I consider the 'Compendium of Drawing'
very thorough and complete for home study, and of excellent value for reference."

INTRODUCTORY OFFER

NOT GOOD AFTER FEBRUARY 28th

BOTH VOLUMES sent free on approval (express prepaid). Keep them five days. If satisfactory send $1.00 and $1.00 per month for five months thereafter. Otherwise notify us and we will transfer them absolutely free. They have a permanent utility that makes them a desirable acquisition to every library.

LIST OF AUTHORS AND SUBJECTS

Part I PROF. E. KENISON, M. I. T. . . . .

. Mechanical Drawing PROF. H. W. GARDNER, M. I. T.

Shades and Shadows PROF. D. A. GREGG, M. I. T. .

Rendering in Pen and Ink PROF. W. H. LAWRENCE, M. I. T

. Perspective Drawing FRANK CHOUTEAU BROWN, Arch., Boston.

Arch. Lettering
Part II
PROF. W. H. JAMES, M. I. T. . . . . . Working Drawing

. Mechanism PROF. C. L. GRIFFIN, formerly Pa. State College . Machine Design WM. NEUBECKER, N. Y. Trade School. Sheet Metal Pattern Drafting

. Tinsmithing

..CUT OFF HERE.. American School of Correspondence, Chicago:

Please send me free, on approval (express prepaid), one Compendium of Drawing, as advertised in The Technical

AMERICAN SCHOOL OF CORRESPONDENCE

CHICAGO, ILL., U. S. A.

World, February

Mention The Technical World.

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St. and No.......
City ......

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Answer: The pressure at any crosssection of the pipe can be determined by multiplying the head in feet at that section by the factor 433. The greatest pressure on the first 300 feet length of pipe will be that due to the head of 18 feet. This corresponds to a pressure of 7.8 pounds per square inch. The greatest pressure on the last section will be that due to the total head of 55 feet, and is equivalent to 23.8 pounds. By use of the following formula, the necessary thickness of the tube can be de

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DXP t = 2X SXE'

If you are interested in any kind of investment,
Oil, Mining, Plantation, Industrial, Lands, Stocks,

Bonds, Mortgages, etc., send us your name and address and we will send you The Investor's Review for three months free of charge. A journal of advice for investors. Gives latest and most reliable information concerning new enterprises, Knowledge is power. Great opportunities come and go. Great fakes likewise. Get posted before investing Write to-day. INSESTOR'S BEVIEW. 15So baff Bldg.. CGICAGO, ILL

Mention The Technical World,

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