102 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



same thinw of otlier lengths. Besirles, there is another consideration 

 which requires attention, namely, the distance of these pins from each 

 other ; since, were they too close, they would counteract tlie object 

 intended, and prevent access of tlie mass of moving heating gases to 

 their sides or surfaces. Indeed, in certain parts of tlie fines, par- 

 ticularly of marine boilers, I believe the heat transmitted will consider- 

 ably exceed the above proportion of nine to one, a point which here- 

 after will be practically illustrated. 



Of the transmitting power of a metallic conductor, if the reviewer 

 will consult "Brande's Manual of Chemistry," (2nd ed. p. 155,) he 

 will there find the doctrine explained, and a diagram, representing the 

 very experiment, as I saw it illustrated by Professor Brande himself, 

 in liis Lectures at the Royal Institution, and which first suggested to 

 me the idea that longitudinal conduction by metallic pins was available 

 for increasing the effective heating suifaces of boilers; and on this 

 ground, that the receiving or heat-absorbing surfaces were large, and 

 the discharging or conveying areas were small— a circumstance which 

 so admirably fell in with the restricted conditions of marine boilers. 

 To this also, I soon found that in practice the system of luiigitudinal 

 conduction had another important feature, namely, that it extended 

 or projected the receiving surfaces, beyond the mere surface of the 

 plate through which the pin passed, and which too often was covered 

 by a coat of non-conducting soot ; and further, that the pins presented 

 themselves to the direct action of the current of heated gases, whereas 

 the plates themselves lay in the same direction and plane of the cur- 

 rent, and therefore receive but indirectly, and in a less degree, the 

 heat of such current. 



Practice has since fully established the correctness of Mr. Brande's 

 illustrations, and the inferences wliich I drew therefrom ; and I can 

 assure the reviewer, that although there were above 1000 persons 

 present, none ventured to call the theory an "absurdity," or imagine 

 that he meant to say that the heat transmitted was in the ratio of 

 the surface and sectional area of the bar he employed. 



The mistake, however, into which the reviewer has fallen, and in 

 the enjoyment of which he revels, has arisen from his overlooking the 

 fact, that this conducting power of a given length of bar, though true 

 to a certain extent, is uevertheless not infinite; and that the mere 

 amount of surface is not to be taken as the measure of the heat trans- 

 ferred. This I have sufficiently explained ; the reviewer, however, 

 led away, no doubt, by the heat of his own imagination, has taken the 

 length of the bar and the stretch of his own fancy as equal measures 

 of inferential absurdity. 



The reviewer observes, "These spikes will, of course, speedily 

 attain the temperature of those particular parts of the flue where they 

 are inserted." This, I take leave to say, is another of the practical 

 errors into which his fancy (or, perhaps, a foregone conclusion that Mr. 

 Williams must be proved to be wrong,) has led him. If this doctrine 

 were true, then we should find the plates also of a boiler attaining the 

 temperature of the flues adjoining, which would at once negative 

 any conducting power. So far, however, from these spikes attaining 

 such high temperature, ))ractice proves, that so long as water is the 

 recipient of the heat they convey, the temperature is, in fact, so low 

 as to be touched without inconvenience, the heat passing through 

 them as fast as it is received, thus preventing such an accumulation 

 of heat as would injure or effect their structure; such, indeed, is the 

 well-known cause of the material of all boilers remaining uninjured, 

 although exposed to very intense heats. 1 here beg to refer to a paper 

 and diagram in the Mechanic's Magazine, No. 9(57, in which I have 

 gone more at large into this important subject. 



I here pass over the strange train of reasoning which the reviewer 

 indulges in, and the equally strange hypothesis he broaches, manifestly 

 from the mistake above noticed ; namely, that "a single spike will be 

 as efficacious as any given number of spikes, provided it have a com- 

 mensurate surface," and the ingenious corollary which follows, that 

 "since a given quantity of spike surface is, by hypothesis, of equal 

 efficiency to the same quantity of ordinary flue surface, an excellent 

 boiler may be constructed wtlhout any fine iurface at all.'" How any 

 one could deduce such extravagancies from the well-known theory of 

 conduction, is not for me to say. Doubtless under the influence of his 

 imaginative powers, the reviewer had forgotten this theory ; for, as 

 Pope observes, 



" Where beams of warm imagination play, 

 The memory's soft image melts away." 



As a plain, matter-of-fact man, however, I beg to refer the reviewer 

 to a diagram (see Mechanic's Magazine, No. 951, containing the very 

 report from which he has so largely quoted,) describing an experiment 

 which he may at any time make. He will there see two boilers de- 

 scribed, having the same extent of flue surface, and Iti every respect 

 alike, with this exception, that one was furnished with conductor pins, 



while the surface of the other was plain. Yet, with the same measure 

 of heat, (from thirty cubic feet of gas,) passing through the flue, the 

 former evaporated S lb. 5 oz. of water, and the latter but 4 lb. 14 oz. 

 Such experiments, which convince ordinary men, however, appear to 

 have no effect upon this imaginative genius and hypothesis-monger, 

 for he observes, of the value of practical experiments, that "though 

 we cannot fail to be convinced by such an argument, we unhappily are 

 not converted." "Unhappily!" I repeat. But we have good au- 

 thority for saying, 



"A man convinced against his will, 

 Is of the same opinion still." 



On the second part of the reviewer's labours — respecting the 

 "smoke-preventive plan," fearing to occupy too much of vour valuable 

 space, I will defer its consideration to my next communication. 



I am, Sir, 



Yours, &c. 

 Liverpool, Feb. IG. C. Williams. 



[We very much regret that Mr. Williams has not favored us with 

 the remainder of his comments, as it is our particular desire that all 

 controversial articles should be brought to a close as soon as possible, 

 and not be allowed to take a range over the Journal for several months, 

 we must therefore request that Mr. W. will conclude his communica- 

 tion in the ensuing journal. We have received two or three other 

 communications on the same subject, which for want of room we are 

 obliged to postpone until next month, when we shall offer some remarks 

 on their contents, as well as on Mr. Williams's communications. — Ed.] 



SANDSTONE. 



Sir — Will you allow me space in your valuable journal, to ask for infor- 

 mation concerning sandstone as a building material ? 



I live in a neighbourhcod which abounds in red and white sandstone, both 

 of which are frequently used for building ; but I have heard many complaints 

 uttered against its use, on account of its great absorption of water, while 

 others affirm that it is equally dry with brick work, provided it be used in 

 the form of rubble work, and well flushed with mortar. It is important, in 

 many places where sandstone abounds, to ascertain its nature with relation to 

 its absorption, because its cheapness renders it very often desirable to use it. 

 Some persons also have great objection to brick buildings, preferring the ap- 

 pearance of the sandstones from the neighbouring quarries, which often 

 present in rubble work a very pleasing and picturesque appearance of warm 

 tints of a variety of hues. 



I am just about to build a house for myself, and should feel greatly obUged 

 by any one favouring me with any facts connected with this subject , par- 

 ticularly as they are of general importance. 



I am, Sir, , 



Your most obedient servant. 

 Sandstone. 



[If our correspondents will refer to the second volume of the Journal, he 

 will find some valuable information on all kinds of stone. — Ed.] 



EVAPOR.^TION OF WATER IN MARINE BOILERS. 



Sir — Can any of your readers state the results of experiments made under 

 their own observation on evaporation of water in boilers for land or marine 

 engines of the usual construction ; the results to be given in the following 

 form ; — Dimensions of boiler — Water evaporated in lbs. — Coals consumed in 

 lbs. — Description of coals used — Time occupied in the experiment. 



I think such information may be applied to some advantage. 



Your obedient servant, 



N. H. A. 



[We refer our correspondent to Mr. Wicksteed's very elaborate experi- 

 ments detailed in a work lately pubUshed, and which was noticed in the 

 Journal of last year. — En.] 



ON THE ORIGIN AND HISTORY OF THE OBLIQUE ARCH. 



Sir — Your correspondent OUver Twist, after describing the Loughborough 

 and Stamford Road Bridge, on the Midland Counties Railway, makes the 

 following assertions : — " The above is a unique specimen, being the only one 

 ever erected, and is the bold invention of Mr. Woodhouse, and was erected 

 in 1839 — 40." As the preceding is an incorrect statement, I beg you will 

 insert in your next number this refutation, in order that, to use your corre- 

 spondent's own words, " the real inventor may have his due meed of praise." 



