1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



2-25 



which brought down the partU in liifge masses ; it was tlii'U loiUiceil into 

 smaller pieces, and carried away in waggons. In this way the wliole of the 

 upper part of the excavation was removed, to the depth of the gullet, by which 

 time a similar gullet was brought up from the commencement of the work, 

 which lowered the excavation twelve feet more; and so on, until the whole 

 was removed ; and each of these steps is called a " lift." 



The new process is the result of necessity, the parent of many useful in- 

 ventions. This excavation was the key to the whole contract, and had to be 

 pushed on with the utmost despatch j and as wages were high and the men 

 intractable, it occurred to the conti'aetor that a plough might be effectually 

 used. The material was a hard, dry marl ; and after a few trials, and by 

 increasing the strength and altering the form of the plough, the plan was 

 crowned with a success far beyond what was originally contemplated ; for in 

 was found that, in addition to dispensing with a number of men, employed it 

 undermining, wedging, and breaking up, it reduced the material to such small 

 pieces, that the labour of several men, who used to break it up at the foot of 

 the embankment, was saved ; and many excavations are now entirely worked 

 with the plough. 



PROCEEDINGS OF SCIENTIFIC SOCIETIES. 



INSTITUTION OF CIVIL ENGINEERS. 

 April 'is, 1839. President in the Chair. 



The following were balloted for and elected : — T. J. Maude, W. Pearce, 

 S. B. Worthington, as Graduates; J. C. Prior, Lieut. R. C. Moody, R. E., 

 as Associates. 



On Steam Sailers and Steam Engines. By Josiah PabivEs, M. 

 Ikst. C. E.* 



In a preceding communication-t- the author had treated of the amount of 

 evaporation in different kinds of boilers in common use; in the present, he 

 treats of their peculiar and relative merits as evaporative vessels ; tlie laws 

 which regulate the amount of evaporation for assigned heated surfaces ; and 

 the practical rules whereby the performance of boileis may be tested. The 

 water evaporated and fuel cousumeJ, had been tabuhiled in the previous 

 communication ; the author now gives the dimensions of the several boilers — 

 the area of the grates — the area of heat absorbing surfaces, and the rates of 

 combustion and evaporation. The connexion of the boiler with the 

 engine as regards the proportion of boiler to engine power, is reserved for 

 consideration in a subsequent communication ; the attention is now confined 

 to the influerice of the proportions of the parts on the performance c.f boilers 

 for a given weight of coal. Evaporation may be considered as the measure 

 of the useful effect obtained from any weight of fuel, or, together with the 

 duty done by an engine, the measure of the useful effect of a given weight of 

 water, in the shape of steam. The author insists on the importance of ascer- 

 taining with accuracy the weiglit of the water, which in the shape of steam 

 has passed through the cylinder of an engine. The weight of water, or 

 quantity of steam, requisite for producing a given effect or duty, was the subject 

 of continual research by Smeaton ; and the basis of Watt's discoveries. 



The author being led to make observations on evaporation twenty years 

 ago, soon perceived that the completeness and rate of combustion, tlie pro- 

 portion of the grates to the combustion effected upon them and to the whole 

 heat-absorbing surface, were important elements in evaporative economy. 

 These elements, in ttie author's own experiments at Warwick, where slow 

 combustion was pushed to nearly its furthest limits — in those of Smeaton at 

 Long Benton — of Rcnnie and Watt at the Albion Mills — of M. de Pambour 

 on the Locomotive Engine, in which intensity of combustion and evaporative 

 power are at their highest limits — of Nicholas Wood on the Killingworth 

 Engine — and of Mr. Henwood, and others, on the Cornish boiler — are the 

 data for the analysis of tiie evaporative effects; the true causes of which in 

 the several experiments, the author now attempts to develop. J The 

 authentic facts here recorded of the working of boilers and engines of 

 established credit and notoriety, will enable the employer of any boiler or 

 engine to compare his practice with specimens of acknowledged and well- 

 attested merit. 



The results derived from the above data are arranged in a tabular form, so 

 as to exhibit at once the relation which any one property and the several 

 parts of the boiler bear to any other, and to the effects produced, the amount 

 and activity of the combustion (to which the author assigns the term calori- 

 Jic forces), and the modifications it experiences by the structure and disposi- 

 tion of tlie several parts. 



There are also certain quantities and relations which exert a peculiar 

 influence over the results, which, being rightly ascertained, are exponential 

 or indicative of the practice of each partioular boiler ; these Mr. Parkes 

 ci"' *'!= exponents of that boiler, and are as follow : — 



The quantity of coal burnt under a boiler in a given time, — the quantity 

 burnt on each square foot of gnafe per hour, — the quantity of water evapo- 

 rated per square foot of heated surface, — and the number of pounds of water 

 evaporated by a given quantity of coal. Besides this, the influence of lime, 

 that is, the time of duration of any given portion of heat about a boiler, and 

 about equal areas of surface, demands our most attentive consideration, and 



» This paper was commenced February 26th, and was continued during four meetings 

 before the Easter recess. 

 + See Transactions, Vol. 9. 

 t The author has beeu unable to obtain any similar data for the Marine Boiler. 



is specially treated of at the close of flic paper. It appears most distinctly, 

 that the boilers tested as to their merit by their respective evaporative 

 economy, arrange themselves in the inverse order of the rate of combustion 

 — the Cornish boiler being greatly superior to all the others when tested in 

 this manner, as well also as in respect if time is selected as the standard of 

 comparison, whereby to mark the scale of descent from the highest point of 

 excellence yet attained in evaporative economy. For this purpose, then, the 

 Cornish results are considered as unity. 



The value of the exponents for the Cornish, Wagon and Locomotive 

 Boiler respectively, are collected together in the following table, will serve to 

 show at one glance the respective values of the boilers on this comparison : — 



The Cornish boiler possesses some peculiar advantages, both as regards 

 structure and the practice of slow combination, shice, by the former, great 

 strength is attained, and, by the latter, time is given for the complete com- 

 bination of air with the heated fuel, for the transmission of heat through the 

 metal, and for the escape of the steam through the water. The plates of the 

 Cornish boiler are usually i an inch thick ; whereas those of a low pressure 

 boiler are usually l-4th to .5-16ths of ,an inch thick; thus a much larger 

 extent of surface is necessary to transmit a given quantity of heat in a given 

 time in the former than in the latter case. The Cornish engineers allow 

 seven times as much surface as in the general wagon boiler practice, for the 

 evaporation of equal weights of water in equal times, and twelve times as 

 much as in the locomotive; from wliich there is a gain of fiom 30 to 40 per 

 cent, in the former, and of 64 with coke and 100 with coal in the latter 

 case. 



The Wagon boiler has great disadvantages of structure, being ill adapted to 

 resist interna! pressure, liable to collapse, and greatly affected by incrustation. 

 According to the above table, which exhibits the mean of eight experiments, 

 the combustion is 2h times more rapid per boiler, and 3 times more rap-d per 

 square foot of grate per hour, and the rate of evaporation is 7 times greater 

 than in the Cornish. The loss of heat, the Cornish being unity, is 24^ per 

 cent. 



The construction of the locomotive boiler is so very different from that of 

 every other species of evaporative vessel, that no strict analogy can be 

 drawn betwixt it and any other. From the above practical results, it appears 

 that the rate of combustion per boiler is nearly 7 times, and per square foot of 

 grate per hour 23 times more rapid — that the rate of evaporation from equal 

 surfaces 12 times more rapid than the Cornish boiler — the loss of heat, the 

 Cornish being unity, 51 per cent. 



The author discusses at length the varying circumstance! connected with 

 different boilers, and the corresponding influence on the above results, and 

 particularly the system of management by which he was enabled with a 

 Wagon boiler to approach the Cornish results. The table accompanying this 

 paper will frequently enable the intelligent employer of a bsiler to ascertain 

 the best proportion of parts, and the best practice. For, having decided on 

 the quantity of steam required, he knows the quantity of fuel which will 

 generate it if he adopts the measures of surface and proportions of parts, 

 which have given relative effects ; or he can ascertain whether his present 

 practice be good or defective. Notwithstanding the great stride which has 

 been made in the economy of fuel by the Cornish engineers, the sources of 

 waste are still great, and we may hope for great advances in evaporative 

 economy, when combustion as a science and practical art has received the 

 attention which it merits. 



The effect of a different practice as regards rapidity of combustion and 

 arrangement of parts, entirely disturbs the relation betwixt boilers of equal 

 surfaces ; the table shows an almost perfect identity in the total, the radiant, 

 and the commimicative areas, between the mean of eight experiments on the 

 wagon and eleven on the locomotive boiler, and the locomotive boiler would 

 present between 3 and 4 times greater surface to absorb the heat generated 

 on the grate than the wagon, if the rate of combustion were the same 

 in both, but the rate of combustion is seven times more rapid in tlie 

 locomotive, and consequently the locomotive does not offer one-half 



■ The results for the Wnfion Boiler are ths mean for eight bgilefp; 



