ページの画像
PDF
ePub

determining the durability of the Bessemer material. On the 2nd of May, 1862, two steel rails were laid down precisely opposite two new iron rails of the best quality, so that no engine or carriage could pass over the iron rails without also passing over the steel. When the iron rails were worn as far as the safety of the traffic would allow, they were turned, the lower side upwards, and the second face was worn off in like manner. The old rail was then replaced by a new one, and this process went on until the 22nd of August, 1865, when one of the steel rails was taken up. It was computed by the engineer, that during the period that had elapsed since it was laid down (three years and about four months) not fewer than 9,550,000 engines, carriages, and trucks, weighing 95,577,240 tons, had passed over one face of the steel rail, and worn it evenly down about a quarter of an inch, whilst it was still capable of enduring a good deal more of the same work. During the same time eight iron rails had been entirely worn out on both faces, and the seventeenth face was in use when the steel rail was taken up. The extraordinary endurance of the new material compared with the old was further proved at Crewe Station, along both sides of which steel rails were laid down, and after three years' wear not one of them required turning ; whilst iron rails similarly placed had been removed or turned every few months.

These results were deemed quite conclusive on the subject ; and, after mature consideration, the Directors of the Company were so satisfied of the advantages in an economical point of view, as well as on the ground of increased safety to the public, of using the strongest and most durable material, that they wisely resolved on erecting extensive Bessemer steel works at Crewe, which are now in active and successful operation, turning out about 400 tons per week. Mr. Ramsbottom, the Company's locomotive engineer at Crewe, had for some time before been gradually introducing steel in the construction of passenger-engines, wherever great strength and durability were required, as in the ase of axles and wheel-tyres; and the results were so satisfactory, that steel is now employed by him in all such cases instead of iron. In designing the machinery and plant of the steel works at Crewe, Mr. Ramsbottom introduced inany ingenious modifications and improvements, so that they may be regarded as models of their kind.

One of his most valuable contrivances for working up the steel required for engine purposes, is his duplex hammer, which strikes a blow on both sides of the ingot al once, in a horizontal direction, thus rendering unnecessary the enormous foundations required for ordinary hammers. The London and North-Western Company have been very

slowly,

[merged small][ocr errors]

are

slowly, and at a great distance, followed by railway companies generally, who are for the most part content, so long as they can, to go forward on the old iron ways. But it seems to us quite clear that the days of iron as the material for main express lines numbered ; and that not only considerations of safety, but of economy, will, before long, lead to the general use of steel instead of iron. The Americans, who are quick to discern the merits of any new invention, have already recognised the important uses of Bessemer steel to a much greater extent than English railway engineers have done. They are already substituting steel for wrought iron in almost every department of railway construction; and within the last few months orders have been received by a single Sheffield firm for about 10,000 tons of Bessemer steel rails for the Pennsylvania, Erie, Philadelphia, Baltimore and Ohio, and Michigan Central Railroads.

Another circumstance remains to be mentioned in favour of the substitution of steel for iron, which is, the great deterioration in the quality of modern-made iron. All the earlier experimenters on iron found greater strength in ordinary qualities than is now possessed by the very best. The rails made thirty years since possessed much more durability than those made now. Whether this arises from the greater rapidity of the processes now adopted, ---the use of squeezers, by which cinder and sand are pressed into the metal, instead of being beaten out by the tilt-hammer as formerly,—the use of the hot-blast, by means of which inferior ores are capable of being reduced, or the spirit of competition which induces iron manufacturers to turn out the largest possible quantity of iron at the cheapest possible rate, --certain it is, that the manufacture of wrought iron in this country has undergone a serious deterioration during the last half century.

Dr. Percy raises an important point for discussion, with reference to a supposed deterioration in the quality of iron resulting from the effects of percussion, which applies equally to steel. It has long been a moot point with engineers, whether, under repeated light blows, or rapid vibration of machinery in action, iron becomes disintegrated and consequently brittle. This is undoubtedly the case with brass, which, when subjected to vibration, in a few weeks becomes as brittle as glass. When the frightful accident occurred on the Versailles Railway, some years since, occasioned by the breaking of a crank axle, the best men of science and practice in France were called upon to give evidence on the point ; but they were by no means agreed. The whole subject was again discussed before the Commissioners appointed by our own Parliament, in 1849, to inquire into the appli

cation of iron to railway structures. Evidence was given to show that pieces of wrought iron exposed to vibration frequently break after long use, and exhibit a peculiar crystalline fracture and loss of tenacity ; whilst other witnesses maintained that this peculiar structure was the result of an original fault in the process of manufacture, and that the internal constitution of the metal remained unaffected by vibration, however rapid or long-continued. In opposition to the popular view as to the brittleness of iron being occasioned by vibration, Mr. Robert Stephenson pointed to the engine-beam of a Cornish engine which received a shock equal to about 55 tons eight or ten times a minute, and yet went on working for twenty years without apparent change. He also referred to the connecting-rod that communicates the power of the locomotive to the wheel, and receives a violent jar eight times in a second at ordinary speed, and yet remains unaffected. He pointed out that in a case of that sort a rod that has borne 200 million of such jars, will be found, on examination, to have retained its fibrous structure,

Where iron exhibits a crystalline appearance on breaking, Dr. Percy rightly points out that time plays a most important part in determining the character of the fracture. When the metal is broken with extreme rapidity, the fracture will be crystalline; when broken slowly, it will be of a fibrous appearance. In the case of the breakage of a crank-axle, we apprehend the cause to be torsion, not vibration. It was stated in evidence by a locomotive engineer, at the inquiry into the causes of the Bow accident on the Great Eastern line, that the very first turn of a crank-axle begins the process of breaking ; and that the final fracture—nearly always at the same place-is only a question of time.

That the brittleness of iron is increased by frost is also a prevalent notion amongst engineers, similar to the popular impression that bones are more brittle in winter than in summer. But the railway accidents which occur in frosty weather are more probably attributable to the circumstance that at that time the road is hard and rigid, and the engines running over it at high speeds are much more strained, and consequently more liable to accident than they are in ordinary weather when the road is soft and yielding; just as in frosty weather we are more liable to falls, and consequently to fractured limbs, arising from the slipperiness of the roads rather than to the increased brittleness of our bones at that season. To

put the matter to a practical test, however, Mr. Ramsbottom had a piece of rail taken up while covered with sharp frost and placed under the large steam-hammer at Crewe, when it stood the blows necessary to double both ends

together

together without showing the smallest indication of fracture. Nevertheless the suggestion of Dr. Percy is well worthy of consideration, in which he says, “It is most desirable that the subject should be accurately investigated ; and the Institution of Civil Engineers would render excellent service by conducting an elaborate inquiry into it."

As for the supply of the ore out of which iron and its inestimable compounds are manufactured, there seems to be no limit to it. Throughout Great Britain it is found in various forms: as red hæmatite in Cumberland and Glamorganshire; brown hæmatite in Staffordshire, Gloucestershire, Glamorganshire, Cornwall, Devon, and the north of Ireland ; spathic carbonates in Durham, Somerset, and Devon ; and argillaceous ironstone from the coal measures in Yorkshire, Derbyshire, Staffordshire, Shropshire, Monmouthshire, Glamorganshire, Pembrokeshire, and in Scotland. Only within the last few years immense deposits of iron ore have been discovered in the liassic and oölitic beds in Yorkshire, Northamptonshire, and Lincolnshire.

There is therefore little reason to apprehend the exhaustion of the raw material of iron, though there are grounds for fear lest the Coal, without which the ore would be comparatively worthless, should by waste, exportation, and increasing consumption for manufacturing and locomotive purposes, become prematurely exhausted. Indeed, the impression begins to prevail that we are drawing far too largely upon our coal deposits, and that in the course of two or three more generations there will be an end of them,-or, at least, that the cost of raising the coal from greater depths will be so much enhanced as to place us at a serious disadvantage compared with our foreign competitors. Our manufacturing power rests mainly upon the cheapness and the abundance of our fuel, of which the supply is limited, though we consume and export it as if it were inexhaustible. We are no doubt exceedingly prosperous at present, and shall probably continue so while we go on raising, cousuming, and exporting at such an increasing rate our treasure of steam-power, so long hoarded up in the bowels of the earth; but unless some new source of power can be discovered, as cheap and available as coal, the greater our prosperity the nearer will be our decay. When our coal is burnt up, or becomes scarce and dear, away will go our iron and steel making, our steam-power, our manufactures, and all the varied industries that depend mainly upon cheap fuel for their prosperity. When that time arrives, as arrive it will, though it may not be in our time, the towns of the North, now so populous, so prosperous, and so rich, will

become

become deserted wildernesses of brick, and fall into decrepitude and decay, like Venice, like Ghent, or like Bruges, but without their art and their beauty.

The same transfer of industry has been witnessed in England before, though on a much smaller scale. When Sussex abounded in timber, it was the great seat of the iron manufacture. The clang of bammers resounded throughout the county, and manufactures prospered in the adjoining towns-at Cranbrook, Rye, Robertsbridge, and Winchelsea-places now in the last stages of decay. But, as fuel became scarce, the iron manufacture of Sussex declined ; and England long depended upon foreigners for its supply of the metal until the fortunate discovery was made that coal could be successfully employed in the reduction of the ore. Then the manufactures of the South were for the most part transferred to the North, and the Sussex glades were left to their original solitude. And such, too, will be the fate of the North when the iron-melters and manufacturers there have burnt up all their fuel.

Not without reason, therefore, does Dr. Percy conclude his admirable volume on Iron and Steel' with these warning words :- Our coal is not only being consumed at a prodigious fate at home, but is being largely exported ; and the question as to the probable duration of our coal fields has of late been discussed with reasonable anxiety. In 1862, we raised 84,000,000 tons of coal, and the demand continually increases. Hitherto, owing to the abundance of our mineral fuel, we have been--and still are--comparatively regardless of economy in its consumption. The time has now arrived when necessity will compel us to act differently, both in our manufactories and our households.'

Art. IV.-Life and Times of Sir Joshua Reynolds, with Notices

of some of his Contemporaries. Commenced by Charles Robert Leslie, K.A. Continued and concluded by Tom Taylor, M.A. With Portraits and Illustrations. 2 Vols. 8vo. London, 1865. TE resume, according to promise, our consideration of the

Life of Sir Joshua Reynolds, and we propose to follow that gifted and worthy man to the close of his distinguished life. We have already said that in the generation which preceded that of Reynolds, English painting had sunk very low. But when art has passed through its various stages of decay till it has lapsed into vapid imitation there is a natural tendency

to

« 前へ次へ »