Scientific American Supplement, No. 484, April 11, 1885

첰Scientific American Supplement, No. 484, April 11, 1885

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Title: Scientific American Supplement, No. 484, April 11, 1885
Author: Various
Release Date: November 3, 2004 [EBook #13939]
Language: English
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[Illustration]

SCIENTIFIC AMERICAN SUPPLEMENT NO. 484

NEW YORK, APRIL 11, 1885
Scientific American Supplement. Vol. XIX, No. 484.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
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TABLE OF CONTENTS.
I. ENGINEERING AND MECHANICS.--Bridge over the Blaauw Krantz Ravine, Cape Colony.--2 engravings.
Torpedo Ships.
The Gas Engine.--By DUGALD CLERK.--Combustion engines.--First cylinder and piston engine.--Watt's experiments.--First gas engine.--Principles of the gas engine.
Rapid Construction of the Canadian Pacific Railway.--By E.T. ABBOTT.
The Osgood Mammoth Excavator.--3 figures.
Capstan Navigation on the Volga.--4 figures.
Steamboat Equipment of War Vessels.--With engraving of winch for raising and lowering torpedo boats.
Improved Steam Trap.--1 engraving.
II. TECHNOLOGY.--Critical Methods of Detecting Errors in Plane Surfaces.--By JOHN A. BRASHEAR.--11 figures.
Photometric Standards.--9 figures.
Bleaching or Dyeing Yarns and Goods in Vacuo.--1 figure.
On the Moulding of Porcelain.--By CHAS. LAUTH.--Moulding by pressure of the air.--Moulding by vacuum.--Drying the moulded pieces.--2 figures.
Photo-Tricycle Apparatus.--1 figure.
A Photo Printing Light.--1 figure.
A New Actinometer.
Astronomical Photography.
Electricity as a Preventive of Scale in Boilers.
III. DECORATIVE ART.--Alphabet designed by Godfrey Sykes.--An engraving.
Old Wrought Iron Gate.--An engraving.
IV. GEOLOGY.--The Organization and Plan of the United States Geological Survey.--By J.W. POWELL.--A topographic map of the United States.--Paleontology.--Chemistry.--Physical researches.--Statistics.--Library.--Publications.--General geology.--Economic geology.--Relation of the general survey to the State survey.
V. BOTANY, ETC.--The Sunflowers.--Annuals, perennials, etc.--11 engravings.
Lye's Fuchsias.--1 engraving.
VI. HYGIENE, ETC.--Brief Sanitary Matters in Connection with Isolated Country Houses.--By E.W. BOWDITCH.
Sanitary Cooking.--By V.L. OPPENHEIMER.
Time required to digest Different Foods.
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THE BLAAUW KRANTZ VIADUCT IN CAPE COLONY.
This viaduct is built over a rocky ravine on the railway from Port Alfred to Grahamstown, at a height of about 200 ft. from the bottom. Its length is 480 ft. 6 in., and the width of the platform is 15 ft., the gauge of the railway being 3 ft. 6 in. The central span of the viaduct is an arch of 220 ft. span between abutments, and about 90 ft. height; the remainder of the space on each side is divided into two spans by an iron pier at a distance of 68 ft. from the retaining wall. These piers are 36 ft. 2 in. high, and carry girders 144 ft. long, balanced each on a pivot in the center. One end of these girders is secured to the retaining walls by means of horizontal and vertical anchorages, while the other end rests in a sliding bearing on the top flange of the arch.
[Illustration: BRIDGE OVER THE BLAAUW KRANTZ RAVINE, CAPE COLONY.]
[Illustration: BRIDGE OVER THE BLAAUW KRANTZ RAVINE, CAPE COLONY.]
In designing the structure the following points had to be considered: (1) That, on account of the great height above the ground, and on account of the high price of timber at the site, the structure could be easily erected without the use of scaffolding supporting it as a whole. (2) That, on account of the high freights to Port Alfred, the quantity of iron in the structure should be as small as possible. (3) That the single parts of the principal span should be easy to lift, and that there should be as few of them as possible. For this latter reason most of them were made in lengths of 20 ft. and more. The question of economy of material presented itself as a comparison between a few standard types, viz., the girder bridge of small independent spans; the cantilever bridge, or the continuous girder bridge in three large spans; the single girder bridge with one large span and several small spans; and the arch with small girder spans on each side. The suspension bridge was left out of question as inadmissible. A girder bridge with small independent spans on rocker piers would probably have been the most economical, even taking into account the great height of the piers near the middle of the ravine, but there would have been some difficulty in holding those piers in position until they could be secured to the girders at the top; and, moreover, such a structure would have been strikingly out of harmony with the character of the site. On the other hand, a cantilever or continuous girder bridge in three spans--although such structures have been erected in similar localities--could not enter into comparison of simple economy of material, because such a design would entirely disregard the anomaly that the greater part of the structure, viz., the