1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



289 



nearer to the centre of E, and consequently carries the ratchet round 

 a greater distance. The slot should of course be made so that G 

 might be carried to the very centre of E, though not so shown in the 

 figure. Instead of a rod, G, a string with a weight or spring for 

 bringing it back might be employed : and instead of the bell-crank, 

 H, a chain or piece of silk or catgut, with a couple of puUies and a 

 spring, might be used. These puUies, or one of them, might mani- 

 festly be made spiral, so as to move the pin of G out and in, according 

 to any desired ratio; or the same effect is accomplishable by a suitable 

 construction of the spring. 



We do not think it of the least use to register the pressure of steam 

 beneath the piston as well as above, in any double-acting engine ; as, 

 if the valves are properly proportioned, the upnor and under pressures 

 must be always the same. It is desirable to ascertain by a common 

 indicator that the action in the up and down stroke is identical ; and 

 then the registration of the difference of pressure during one part of 

 the stroke will be a correct indication of the engine's performance. 



We are glad to find that Professor Moseley's indicator is about to 

 be applied to the Great Western, and we anticipate vast benefit to 

 steam navigation from its application to steam vessels in general. We 

 trust Professor Moseley will urge the advantages of such a species of 

 registration upon the attention of steam ship owners. It is of the last 

 importance, and the public is greatly indebted to Professor Moseley 

 for his successful labours in removing many of the difficulties which 

 stood in the way of the establishment of a comprehensive and efficient 

 system. We shall be greatly disappointed if he fails to follow these 

 labours up, or neglects the steps necessary to render them beneficially 

 available in practice. Some representation should be made to the 

 Steam Association on the subject. 



THE ELEMENTS OF STEAM IlfPROVEMENT. 



One of the most important improvements in the steam engine developed 

 of late years is expansion ; and although it can scarcely now be called 

 an irnovation, yet it has not, up to the present time, come into uni- 

 versal use, and where adopted, has not been carried to that degree to 

 Vfhich it might be beneficially extended. In Cornwall, it is true, ex- 

 pansion has accomplished the greatest wonders, and in our largest 

 steam vessels the most eminent benefit has been derived from its use ; 

 but in many steam vessels, expansion is very little or not at all prac- 

 tised, and in those in which it has been carried farthest, it has not, we 

 think, been carried sufficiently far. We know it will be objected to, 

 that to carry expansion much farther in steam vessels would require 

 high pressure boilers, and that such boilers are too dangerous to be 

 admissible. But we do not think high pressure boilers, if made as 

 they ought to be made, in the least more dangerous than the low pres- 

 sure boilers in ordinary use. On railways they are regarded without 

 apprehension; and among the innumerable locomotive boilers in use, 

 there has been scarcely any example of accident. There would, 

 therefore, seem to be no good objection to locomotive boilers in steam 

 vessels on the score of danger, and they have already been introduced 

 by Messrs. Bury and others in river steamers with eminent success. 

 But there is a serious objection to tbem in the case of sea going 

 steamers, in consequence of the deposition of scale, which would soon 

 prove destructive to the brass or copper tubes. This difficulty, how- 

 ever, is surmountable by the use of some of the contrivances already 

 before the public for keeping the boilers supplied with fresh water ; 

 and the necessity of those contrivances to locomotive boilers, confers 

 upon them an importance to which they would not otherwise be en- 

 titled. 



There are two modes of returning the same water continuously to 

 the boiler, so as to obviate the necessity of replenishing the boiler 

 with water from the sea — the one is to condense the steam by the 

 interposition of cold surfaces, the other to cool the water which lias 

 become heated by the condensation of the steam, and use it over again 

 for the purpose of condensation. The first plan is that carried out in 

 Hall's condensers, and in the condensers of Mr. David Napier and 

 others ; the second is known as Symington's system of refrigeration : 

 and we think it important to inquire which of these plans is the least 



objectionable, and whether one of them, at least, may not be carried 

 out in practice without giving rise to evils that will more than neu- 

 tralize the benefits derivable from an extension of the principle of 

 expansion. 



The condensers of Hall require to be provided with large pumps 

 worked by the engine ; they occupy considerable room in the ship, 

 and the weight of water and weight of metal in them are both very 

 great. The refrigeratory pipes require to be made strong enough to 

 resist the atmospheric pressure, and all the joints, of which there are 

 a vast number, require to be particularly good for the same reason. 

 These are serious objections, and another, also of considerable weight, 

 is to be found in their expense. Condensers for engines of 300 H. P. 

 cost several tho\isands of pounds, and contain about ten miles of pipe. 

 Mr. David Napier's condenser is only applicable in the case of iron 

 vessels, and has the same disadvantage as Hall's in having the pres- 

 sure of the atmosphere to sustain. It is, however, less expensive, but 

 is rather susceptible, we apprehend, of derangement from leakage, 

 and it is almost impossible to repair it when deranged. Symington's 

 plan consists in leading a flattened copper pipe proceeding from the 

 hotwel! forward and aft on the outside of the ship near the bilge, so as 

 to be always beneath the water, and out of the reach of injnrv either 

 from ice, barges, or buoys, as well as from the ship taking the ground. 

 This pipe is so made as to possess the requisite surface for cooling 

 down the water proceeding from the hotwell to the temperature ade- 

 quate for injection ; and is at the same time so nicely fitted to the 

 vessel as not to constitute any appreciable impediment to her progress. 

 Indeed, we do not see why this pipe might not be so constructed as to 

 form jDro tanlo the copper of the vessel, which, in effect, it would be 

 if made with only a very small projection and a considerable depth. 

 In Symington's plan this pipe forms the whole apparatus — there are 

 no pumps or other machinery to work, and as the condensation is not 

 performed within the pipe, it has no atmospheric pressure to sustain, 

 and therefore may be made of light materials, and without any par- 

 ticular care in jointing. Indeed, even if there were a hole purposely 

 made in the pipe, it is very questionable whether a drop of water 

 would leak either in or out, the pressure within and without being 

 just about the same. 



It would be foreign to our present purpose to enter into anv enu- 

 meration of the various benefits to be derived from feeding marine 

 boilers with fresh water. It is sufficient to say that they are eminent 

 and manifold, and involve, to a considerable extent, the question of 

 economy of fuel. In muddy rivers, too, it is very important, after 

 starting with clean water in the boilers, to use the same water over 

 and over again, and we believe that, in such situations, this will be 

 found the only remedy for priming. But these considerations, though 

 important, are poor and insignificant compared with those which flow 

 from an effectual extension of the principle of expansion in steam ves- 

 sels, and to which the use of fresh water in the boilers is, in our 

 opinion, indispensable. 



We understand that Symington's plan of refrigeration has been 

 applied to several steam vessels with eminent success; but one vessel 

 to which it was applied, the Cil;/ of Londonderry, it svas subsequently 

 removed from. This certainly looks unfavourable ; yet, if the plan 

 has been found to answer well in the case of some vessels, it is diflSoult 

 to perceive why it should fail to answer universally. The most natural 

 supposition therefore is, that the failure in the case of the Citi/ of 

 Londonderry was the result of accidental circumstances, such as will 

 often befall the best devised schemes, b\it which are always suscep- 

 tible of rectification. As we happen to be intimately acquainted with 

 the causes which led to the removal of Symington's apparatus in this 

 particular instance, we shall briefly state them, partly as an act of 

 justice to that scheme, and partly to exemplify how easily the most 

 trivial and irrelevant circumstances may sometimes conspire to con- 

 demn and render vain even the best contrived arrangements. 



Anteriorly to the application of Symington's plan, the City of Lon- 

 donderry was an old and had always been a slow vessel : it was resolved 

 upon to lengthen her, with the view of increasing her speed, and the 

 occasion of this alteration was seized upon for the application of 



