Another surprise, but of a more agreeable nature, occurred in the shape of a sudden demand for this work from America, whereby the First Edition was at once exhausted. Before then it had been intended to devote three years to the revision, and some elaborate work had already been taken in hand, notably the summarising and tabulating of recent experiments on boiler strengths and on steam and water, but when the demand for a Second Edition came, and a choice had to be made between issuing a reprint at once or delaying the publication for some considerable time, the latter alternative was decided upon, for it was hoped that the additions already in hand, amounting to about sixty pages, and including a short chapter on steam, water, and the boiling phenomena, would be considered worth waiting for.

An apology is also due for the omission of detailed accounts about water-tube boilers. These boilers occupy a peculiar position, being monopolies of various firms. To praise one type as compared with another, is to lay oneself open to a charge of favouritism; to speak plainly about defects, is to bring oneself into conflict with patentees. Besides it is only with great difficulty, and then in strictest confidence, that one can obtain first-hand information about mishaps. To explain the tools and methods of construction is to divulge workshop secrets; and the result is that papers on water-tube boilers have as yet been rather sketchy or one-sided. It was not thought advisable to repeat such matter, but this work contains a full list of these papers, which can be consulted. The case would have been different if the Admiralty Committee on Water-Tube Boilers, which is still sitting, had concluded its labours; then there might have been some definite information to go upon. It might even have seemed advisable to await their report before publishing this Edition; but on the other hand it must be remembered that the last Admiralty Committee on Boilers, after collecting a thick volume of most valuable evidence, did not publish it, in deference to the wishes of a few high-placed witnesses, and the same might happen again. The temptation to follow this example will of course be great, but in the interests of Marine Engineers it is hoped that all obtainable information on water-tube boilers will soon see the light of day.

C. E. S.

MANCHESTER: June 1901.

PREFACE

ΤΟ

THE FIRST EDITION

WHILE reading through these pages for the last time, and thereby completing a task which has proved a heavier one than could at first have been imagined, numerous passages have recalled to mind friendly discussions of which they are the outcome, or valuable hints and sometimes exhaustive criticisms from those friends to whom doubtful points were submitted. Should they find that their views have not in all cases been adopted, the text will doubtless also reveal to them the reasons why this could not be done; and to these friends I wish to convey my warmest thanks for the encouragement which their personal interest in this work has afforded me.

While collecting the material for this work a feeling that many problems yet remain to be solved has rarely been absent from my mind, more especially when the scientific side of a question was being inquired into. Not being in a position to satisfactorily discuss such problems, it seemed necessary at least to state them concisely, so that scientists might be induced to solve them for us. It would have been very easy to ignore such difficulties altogether; but this course would have been contrary to my purpose, which was to produce a work of a practical character. If it should be objected that just because of this object even the simplest mathematics ought to have been omitted, such critics should remember that true practice, unlike abstract science, is unscrupulous in the choice of means, and avails itself of the gratuitous labours of scholars and scientists as readily as it adopts the more costly experiences gained by repeated failures. Besides, as the object of science is truth, practical men, whose sole aim is success, dare not remain in the dark as regards its discoveries and deductions.

GLASGOW August 1893.

C. E. S.

INTRODUCTION

THE information contained in this work has been collected for the use of people interested in the manufacture and management of marine boilers, and it is hoped that the summaries of the experiences gained in one of the branches with which it deals will assist those whose attention has been confined more particularly to the other. Thus, for the information of manufacturers, it was necessary to discuss the troubles to be expected from the use of defective materials, as well as the dangers to which a boiler is exposed after it leaves their hands; while for steam users, descriptions as to the processes of construction, and scientific inquiries about corrosion, fuels, and similar subjects, had to be brought together.

In spite of a very exhaustive search, extending over several years, little information either about the management or about workshop practices could be found, most books and papers professing to deal therewith doing so only in vague terms. The Author had, therefore, to rely mainly on his own experiences when explaining the various practices and manipulations. Although it was impossible to enter into every minute detail, it is hoped that no points have been omitted to which attention should be drawn.

In writing the chapter on 'Mechanics' the Author also had to rely mainly on his own resources when trying to present such problems as occur in marine boilers in as simple and yet as comprehensive a form as possible. Special attention has there been paid to the relations existing between elastic stresses and those which make their appearance just before rupture takes place, whereby it is hoped that the term 'factor of safety' has acquired a more precise meaning than it at present possesses. A graphic method for resolving stresses, a method for estimating the shearing strengths of a material from torsion experiments, and a discussion on the irregular distribution of stresses in

riveted joints, are some of the subjects herein discussed, and about which little will be found in earlier books.

In the chapter on Corrosion' attention is drawn, amongst other matters, to the strange influence which apparently harmless salts exert on the harmful activity of weak acids; the action of air in feed-water and the much-debated question of galvanic currents in boilers have been treated in some detail.

While examining the numerous experiments on 'Heat Transmission,' and before Mr. Durston's excellent paper was read, the Author was confronted with the serious difficulty that nearly all these experiments are incomplete as regards certain essential points. Sometimes the heating value of the coal was not stated; sometimes the steam pressure, funnel or feed temperature was forgotten, or the ashes not weighed; but by having brought together various experiments in one chapter a better idea can now be formed than has yet been possible about the resistance encountered by heat when it travels from the flame through the iron. and scale into the water.

Somewhat similar remarks might be made on the subject of 'Strength of Materials,' for metallurgists are still unable to explain why a metal which can be stretched from 20 to 30 per cent. in a testing machine sometimes shows no plasticity, and cracks spontaneously, when fitted in a boiler. Pains have been taken to collect all references to such influences as might cause trouble when using steel, and it is hoped that the Author's experience, both in engineering works and in numerous English and foreign steelworks, has led him to touch upon everything that is essential.

The chapter on Fuels and Combustion' ought to be of value to those who are entrusted with the carrying out of accurate experiments on the performances of engines and boilers. Not only has it been explained there how necessary it is to know the heating value of the fuel used, and whether it has been properly burnt, but explanations have been added showing how to carry out the experiments, and as they are comparatively simple, seagoing engineers possessed of a knowledge of chemistry might easily inform themselves on questions such as how much heat and unconsumed fuel are escaping up the funnel, and how much priming water is carried over with the steam, about which points reliable information is still wanting.

For the convenience of draughtsmen the rules of the Board of Trade and of Lloyd's Register on the scantlings of boilers have all been placed near the last pages, and much trouble has been taken to make