1849.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



89 



rier in our path. Man has succeeded in rendering almost every quality of 

 every various form of material substance available for some purpose of 

 utility. On certain occasions only, and for certain purposes, some one or 

 other of those qualities will be found to stand in the way of his success. 



Chemistry has gone far towards establishing the hypothesis that all 

 natural bodies are susceptible of assumirig three forms — the solid, fluid, 

 and gaseous. — according to the degree of beat by which they are atfected. 

 At all events, it is certain that heat exercises, in various proportions, such an 

 influence on the constituent atoms as to destroy or diminish their mutual 

 attraction ; and even when the mass does not subside into fluidity, it loses 

 its strength and cohesive properties, and becomes disintegrated. The uses 

 to which this property of matter have been applied are infinite. Let us see 

 how it may become a limitary principle. 



It is supposed that the possible heat of a burning atom (in which of 

 course we shall find the theoretical limit) is very far above the highest 

 known temperature attained in our furnaces; and it would consequently 

 follow that we might more nearly approach that limit by varying the ar- 

 rangement of the fuel and tlie supply of air for combustion. This has been 

 accordingly done, until we have found our progress stopped by the impossi- 

 bility of discovering any substance whereof to build our furnaces, which 

 will bear the heat. Porcelain, fire-brick, and plumbago, in various combi- 

 tions are adopted : but they either crumble or sink down into a pasty mass, 

 as the fire is urged. The qualities of matter itself here act as a complete 

 estoppel: and if we would experimentalize further upon the phenomena of 

 caloric, we can operate only upon a minute scale by means of the gas blow- 

 pipe, or the heated arch evolved from charcoal points interposed in a gal- 

 vanic circuit. But for this limit, many useful purposes might be accom- 

 plished, by the mutual actions or changed forms of material bodies when 

 subjected to the intense action of heat. For instance, in the case of plati- 

 num, — we might then separate it from its ores by the ordinary methods of 

 smelting and fusion; in place of being compelled to adopt the laborious and 

 costly process of solution in acids. The steam-engine offers an example 

 nearly parallel. The power of a steam-engine depends primarily upon the 

 area of surface exposed to the action of the fire, and the intensity of the 

 fire itself. In marine and locomotive engines, where space must be econo- 

 mised, the practical limit is fixed only by the degree of heat; and this, of 

 course, must be kept below the utmost limit which the material of the 

 boiler furnace will endure. As yet, there has not been discovered any 

 niateiial better fitted for this purpose than iron ; and we have made our 

 fires as fierce as the melting point of iron will permit : even now, the fire- 

 bars are destroyed socnetimes upon the first journey. 



Farther than this we obviously cannot go, so long as we use water for the 

 power-producing agent. Attempts have however been made, to conquer 

 the difficulty by taking advantage of some other properties of matter in its 

 relation to beat; based upon the fact that the "evaporating point" — that is, 

 the degree of heat at which fluids expand into vapour — is found to differ 

 considerably in different liquids, just as does the melting point of solid 

 bodies. It would therefore appear probable that, by filling the boiler with 

 alcohol, which boils at 173", or with ether boibng at 96° Fahrenheit, the 

 tension of the vapour and consequent power of the engine, could he in- 

 creased without increasing the heat of the furnace. As both of the above- 

 named fluids are expensive, it was first requisite so to contrive the machine 

 that no loss should be experienced, but the whole vapour be recondensed 

 and returned to the boiler. For this purpose a variety of ingenious con- 

 trivances have been suggested, the earliest of which, and one perhaps as 

 efl'eitual as any other, was patented by Dr. Cartwright, in 1797 ; while new 

 forms of mechanism, with the same object in view, are even still appearing 

 on the patent rolls from time to time. Whatever the ingenuity of man 

 could do, has probably therefore been done : but the practical utility of all 

 these contrivances was destroyed by the influence of other properties of 

 matter altogether overlooked, although of necessity involved in the question. 



These regard the relative bulk of the vapour produced from correspond- 

 ing quautilies of dili'erent fluids, and the proportion of heat absorbed or 

 rendered latent in each during the process of vaporisation. The calcula- 

 tion is sufficiently simple; and the result eft'ectually annihilates all hope of 

 advantage, either potential or economical, from the etiierial or alcoholic 

 engines. Thus, to convert a given weight of water inlo steam, 997° of 

 heat are required as wliat is called *' caloric of vaporization.'' The same 

 quantity of alcohol will become vapour with 442°, and sulphuric ether 

 with only 302°. Kut to set aRaiust this appareut gain, we find thai tlie 

 specific gravity of steam (air being = 1) is -0235 ; vapour of alcohol 

 rtiOS ; ether 2'5Sfi ; and the result may be thus tabulated. 



Caloric of Spec. Grav. Useful effects 



Vaporization. of Vapour. of Caloric. 



Water 997° -6235 10,000 



Alcohol 442° l-eoS 8,776 



Sulph. Ether 302° 2-5b6 7,900 



The disadvantage ol the latter fluids will be farther enhanced by the 

 circumstance that, being lighter than water, a larger boiler will be re- 

 quired to hold the same weight of vaporific fluid :— i.e., a pound of water, 

 when evaporated, will form about 21 cubic feet of steam; while a pound 

 of ether will require a larger boiler to hold it, and will only form 5 cubir 

 feet. 



Weight is one of the properties of matter which in practice we encoun- 

 ter chiefly as an obstacle or inconvenience, tending to increase friction, to 

 resist motion, and generally to crush and destroy. Meanwhile, the limits of 



its range are comparatively narrow — that is to say on one side. We can, 

 indeed, rarefy a gas until its weight disappears in infinite tenuity ; but we 

 very soon find ourselves at the extreme verge of any possible increase of 

 specific gravity. The most ponderous substance known is not quite twenty- 

 two times heavier than water. And yet there are many purposes for which 

 bodies of greater weight might he made useful. If, for example, closer or 

 deeper search amid the stores of the mineral kingdom should lead to the 

 discovery of some substance bearing the same proportionate gravity to 

 platinum, that platinum does to cork, how many possibilities of improve- 

 ment would he placed wiihin our power ! A thin sheet of such a substance, 

 interposed among the keel timbers of a ship, would give stability and other 

 sailing qualities at present unattainable. Blocks of it would afford sure 

 foundations for piers, bridges, and all marine works. It might then be 

 found no longer impossible to establish a lighthouse on the Goodwins. As a 

 regulator, or reservoir of power — for counterpoises, pendulums, and fly- 

 wheels ; for all purposes where percussive force is required; and in steam- 

 hammers, pile-drivers, and shot of long range, the utility of such a sub- 

 stance would be enormous. In each and all of these objects, we are limited 

 by ihe limits of specific gravity in our materials. 



The " Strength of Materials" is an element that enters inlo almost every 

 calculation of the mechanist ; and it is found to coustitiite not only an ab- 

 solute limit to all possibility of advance iu certain directions, but also a 

 relative limit universally, when we attempt to reduce beyond certain pro- 

 portions, the size, weight, and cost of our mechanical erections. Its 

 variations also are extensive bolh in degree and in condition. Some bodies 

 offer strong r'esislance only to certaiu modes of attack. Impervious ou 

 one surface, they will yield and splinter into laminae under a slight blow 

 upon another. Some will bear pressure to an euornious extent, but are 

 easily torn asunder; others resist the divellent forces, but crumble under a 

 light weight. A very extensive variety of substances possess a fibrous 

 texture, and are endowed with vast strength to resist a strain iu the direc- 

 tion of their lenglh, but are much weaker agaiust a lateral or transverse 

 foi'ce. This dilierence is found to vary to an intioite extent ; from that of 

 certain metals where the advantage is only four or five per cent, in favour 

 of the direct resistance, to the vegetable and aminHl fibres, such as flax or 

 silk, which possesses enormous tenacity, combined with most complete 

 flexibility. 



The variations in the natural properties of bodies have given infinite 

 scope for the exercise of human ingenuity. In Ihe erection of eiigiueering 

 works, and in a still higher degree iu the contrivance aud construction of 

 moving machinery, the combination of theory and practice is perpetually 

 exhibited in surprising perfection. By nice calculation of the opposing 

 forces, together with great practical skill in the mechanical details of con- 

 struction, we can now attain a result in which abundant strength is united 

 with the utmost possible economy of space aud material. There is no 

 waste ; no addition of useless and cumbrous weight: all irregular strains 

 are skilfully couuterbalanced, and the greatest pressure distributed over 

 the points of greatest resistance. Experience has entitled us to place im- 

 plicit confidence in the scientific precision of our engineers. Every day 

 we trust our lives and fortunes, wiibout misgiving, into situations where a 

 slight error in the calculations, or a slight defect iu the workmauship, 

 would inevitably lead to some terrible calastrophe. How little do tlie 

 crowds who throng the deck of a Thames or Cljde steamboat, or who 

 allow themselves to be hurried along at fifty miles an hour iu a I'ailway 

 carriage, reflect upon the delicate condilions which must have been fulfilled 

 — the complicated rnechanrcal problems which must have been solved, la 

 order that they might accomplish their journey in secur-ity. A multitude 

 will gather upon a suspension bridge without fear or danger, although the 

 rods by which the massive roadway and its living freight are sustained ap- 

 pear as mere threads in comparison with the mass they have to support : 

 while, if any one reflects at all upon the matter-, it is to assure hrmself that 

 every possible amount of pressure has been theoretically provided for ; and 

 that, praciically, every separate bar and joint has been severely tested, so 

 that no single Haw in the material, or defect iu the workmanship can have 

 passed without detection. Krrbourg, before the civil war of the Sonder- 

 bund had given it a political notoriety, was celebrated chiefly for its wire 

 bridge, hung at an altitude of uearly 100 feet between two summits. " It 

 looks," says a recent li-aveller, " like a spider's web flung acr'oss a chasm, 

 its delicate tracery showing clear and distinct agaiust the sky." Dili- 

 gences and heavy wagons loomed dangerously as llrey passed along the 

 gossamer fabric. 



The force that enables a suspension bridge to sustain itself is, what we 

 have called the cohesive force, and is due, we must suppose, to some variety 

 of the attractive principle among the corpuscular atoms, which causes 

 them to resist a separating or divellent strain. In ordinary bridges and 

 among the usual erectrons of architects, on the other hand, the pressure to 

 be considered is that which crushes the parts together. To resist this, the 

 piers of the bridge must have strength sufficient losupport the loaded arch ; 

 and the pillars of the cathedral to sustain the fretted vault that rests upon 

 them. In this case we tiud that the strength which arises from the co- 

 hesion of the atoms between themselves is increased by that due to another 

 quality of matter — namely, its rncompressibiluy. When any solid body 

 yields to a crushing weight, the consequent efl'ect must be, either that its 

 particles are actually pressed into a smaller space ; or that, being made to 

 exert a wedge-like action upon one another, llie exterior layers are forced 

 out laterally. The addition of a band or hoop will then bring the incom- 

 pressihility of the atoms more fully into play : and bodies that are eu- 



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