12 



THE CIVIL ENGINEER AND ARCHITECT S JOURNAL. 



[January, 



the progress of its combustion. He is, liowever, unreasonably fas- 

 tidious witli respect to certain received expressions, and frequently 

 diverts the reader's attention from the immediate object of inquiry by 

 ill-timed repetitions and observations, which render the perusal ex- 

 ceedingly tedious. 



The 1st section treats of the constituents of coal, and the generation 

 of coal-gas. In reading this, we were surprised to find that the 

 author, who is so strenuous an advocate for accuracy of expression, 

 even where it does not afl'ect the facts considered, has himself, in one 

 instance, made use of an inappropriate term, and that in a case where 

 it has a tendency to mislead as to the main fact on wliich he is dilating. 

 In the 22nd page he considers coal as consisting of two portions, viz., 

 " the carbonaceous or solid, and the bituminous or volatile portions." 

 Farther on he observes : 



"The first leading distinction is, that the bituminous portion is 

 com crtible to the purposes of heat in the gaseous slate atone; while 

 the carbonaceous portion, on the contrary, is combustible only in the 

 solid state ; " and again, 



"The bitumen of the coal, by reason of the great proportion of 

 hydrogen which it contains, absorbs heat with great avidity, the first 

 result of which is its change from the state of a solid to that of a tarry, 

 viscous, semijluid ; and, subsequently, by further increments of heat, 

 to the state of gas, with its enormously expanded volume." 



These quotations sufiiee to show that the gases which result from 

 the application of heat to coal are considered by the author to be 

 produced by a simple distillation of the bitumen contained in the coal, 

 which suffers thereby no alteration in its chemical composition; 

 whereas the truth is, that they result from the chemical decomposition 

 of the bitumen, which, by the agency of heat, is resolved into a volatile 

 portion, which is evolved in the gaseous form, and an excess of 

 carbon, which remains behind in the solid state. Or rather, the coal 

 should be considered as originally a homogeneous substance, which, 

 by the action of heat, is first fused, and afterwards, when its tempe- 

 rature becomes sufficiently elevated, is decomposed as above. It will 

 be evident, from these remarks, that the exjiressions "bitumen" and 

 "bituminous portion" ought to be rejected, and "gases" and "gaseous 

 or volatile portion" substituted in their place. 



The 2nd section, which contains merely some general notions of 

 gaseous combinations, is very tedious, and might, without detriment 

 to the work, be omitted. We shall, however, just quote one specimen 

 of the sujierfiuous observations with which this work abounds. We 

 read, page 3(i, 



" Although, for the purposes of the/;(n!aee, so much value is set on 

 the solid carbonaceous portion — the coke, we must not, on that ac- 

 count, undervalue the heat-giving properties of the gas. Indeed, the 

 extent of those powers is strikingly brought before us by the fact that, 

 for every ton of 2U cwt. of bituminous coal, no less than 10,000 cubic 

 feet of gas are obtained, for which we pay at the rate of 10s. for every 

 lOUO feet; the heating and lighting properties of the gaseous portions 

 alone of one ton of coals thus costing five pounds sterling." 



Is this fact a proof of the great value of coal gas as a heat-giving 

 body ? Certainly not ; it is, on the contrary, rather an evidence of 

 the great quantity of heat expended in evolving the gas, which is no 

 advantage, but very much the reverse. This, however, is not the 

 question ; for, unless we are content to use coke from the gas-works, 

 we must be at the expense of separating the gas from the carbona- 

 ceous portion of the coal, and all that remains to be considered is, 

 what amount of heat is the gas, when separated, capable of evolving, 

 how we can utilize the greatest possible proportion of that heat, and 

 lastlv, whetlier the amount gained is worth any additional expense 

 whicli may be incurred in its attainment. 



The yrd section makes us acquainted with the proportions of carbon 

 and hydrogen which constitute carburetted hydrogen gas, and with 

 the quantity of oxygen necessary for the combustion of each of its 

 constituents, as well as the quantity of atmospheric air which is 

 requisite to furnish that quantity of oxygen. It should be here ob- 

 served that the author has applied the term " atom" to atmospheric 

 air, solely for the purpose of reducing the latter to an unitbrmity with 

 the other gases concerned, being perfectly sensible that atmospheric 

 air is not a chemical combination, but a simple mixture of oxygen and 

 nitrogen gases, not exactly in the proportions required by the theory 

 of chemical equivalents, the volume of the oxygen gas being 21 in- 

 stead of 2U per cent, of the whole volume of air. This diflerence is 

 neglected for the sake of simplicity. We have also to point out an 

 error in page o 1, lines 0, 10, 13 and 14, where " eight atoms of air " is 

 put for " four atoms." 



This section is followed by an explanation of two diagrams, repre- 

 senting the combustion of carburetted and bi-carburetted hydrogen, 

 ■which present the volumes of gases used, and of the products of com- 

 bustion, certainly in a very striking form, to the imagination of the 



reader, but we doubt whether a simple table of volumes would not 

 have answered the purpose equally well. 



In tlie 4th and .")th sections the author disposes of the questions of 

 the qhuntity of air rtquiredfor the combustion of the carbon, after the gai 

 has ban generated, and of the quality of the air admitted to a furnace. 

 The lith section treats of the incorporation of air nilh coal gas, and the 

 time required for effecting the same, and the 7th of the mode of effecting 

 that incorporation in the furnace, preparatory to combustion, which are 

 very important points to be considered in the present investigation. 

 In the latter the author explains the principle of his patent furnace, in 

 which the air is introduced to the gases evolved from the coal bv 

 means of tubes pierced with numerous small orifices, tlie effect of 

 whicli arrangement is compared to that of a blow-pipe. 



The Sth and last section of this Part has reference to the place or 

 situation where the air may be admitted into the furnace, so as to act its 

 part with the greatest effect ; and the conclusion arrived at is, for 

 reasons therein developed, that the air for the carbonized fuel on the 

 bars must come from the ash-pit, and that that for the gas must be 

 introduced beyond the bridge. 



Pambour on Locomotive Engines. London; John Weale, 1840. 

 (Second Notice.) 



In our last number we were unable, for want of time, to give more 

 than a very brief notice of this work, but we hope this month to make 

 amends by analysing it throughout with that care which its importance 

 deserves. 



The mode of investigation adopted is briefly explained in the fol- 

 lowing paragraph, which we quote from the introduction of the first 

 edition. 



"The method constantly followed consists in taking, first, the pri- 

 mary elements of the question from direct experiment ; then making 

 use of those elements to establish a calculation in conformity with 

 theoretical principles; and, lastly, submitting the results to fresh and 

 special experiments, in order to obtain their verification. For the 

 further elucidation of the formula, they are each time carefully sub- 

 mitted to particular applications; and, finally, to extend the use of 

 the work to persons who raav wish to find the results without calcula- 

 tions, the formulae are followed by practical Tables, suitable to the 

 cases which occur most frequently in practice." 



The work is divided into IS chapters, in which the various divisions 

 of the subject are treated, followed by an Appendix, shewing the 

 Expenses of Haulage by Locomotive Engines on Railways, from the 

 Accounts of the Liverpool and Manchester, and the Stockton and Dar- 

 lington Railways. 



The first chapter is merely a description of a Locomotive Engine, 

 and therefore needs no comment. 



The second chapter, as we mentioned in our last number, is nearly 

 a copy of the corresponding chapter of another work by the same 

 author, entitled "Theory of the Steam Engine," a review of which will be 

 found in the 2nd volume of this Journal, page 466. The present work 

 contains, however, besides, in the 6th section of this chapter, a Table 

 of 37 of the experiments made by the author with the view of ascer- 

 taining whether or not the steam left the Engine in the saturated state, 

 that is, with the maximum pressure and density corresponding to its 

 temperature, which experiments were merely alluded to in the above 

 mentioned work. The results of these experiments are truly remark- 

 able, since there is no exception to the perfect coincidence of the 

 pressures, on the one hand, indicated immediately by the air-gau^e, 

 and on the other, calculated from the temperature marked by tlie 

 thermometer. But, surprising as this coincidence is, we would by no 

 means conclude therefrom, that such results were not actually obtained, 

 being convinced of the fact which it tends to prove, viz. that the steam, 

 after passing through the cylinder, leaves the engine in the saturated 

 state ; we would rather infer that the experiments were made with 

 extraordinary care and with every precaution to avoid error. 



The third chapter treats of the Pressure of the Steam, and Article- 

 I. of the Safety-Valves in particular. 



After explaining, in the 1st section, the mode of calculating the 

 pressure according to the levers and the spring- balance, the author 

 indicates, in the following section, the corrections to be made to the 

 weight marked by that instrument. And here we cannot but express 

 our dissent from the doctrine laid down with respect to the eftect pro- 

 duced by the rising of the safety-valve on its surface exposed to the 

 pressure of the steam. We read, page 90, 



" ; but whenever the steam, being generated in 'greater 



quantity than it is expended by the cylinders, escapes with force 

 through the valve, it raises considerably the disk of the valve : the 

 consequence then is, that, instead of acting merely on the inferiorsur- 



