1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



399 



duty, which was for six hours only,) by the engine, coals from the 

 same heap being used." The experiment lasted ISj hours. In these 

 16 observations the highest duty was 118,522,475 t1>. lifted one foot 

 high witli 04 16. of coals, the lowest 03,650,298 It)., and the average 

 Sli,4S0,U18 16. From which it appears that the A; "'^ts/ duty was 37 

 per cent, above the mean, and the hivesi 26 per cent, below the mean. 



" Finding the disparity so very great in these experiments," the 

 author "commenced a fresh series, with a view of ascertaining the 

 actual evaporation of water with cylindrical and wagon-head boilers 

 under different circumstances of surface exposed to the action of heat, 

 of coals burnt per square foot of grate, of quantity of water evaporated, 

 and, as regards the wagon-head boiler, /eith and without clothing: 

 wishing also to ascertain the comparative merits of the tw'O engines, 

 he recorded the average quantity of water used per strolce in the form 

 of steam." 



The following statements are calculated to give weight to the re- 

 sults recorded by Mr. Wicksteed in the work before us. 



" The time occupied in the trials upon the cylindrical boilers was 

 above 3400 hours, the coals consumed above 900,000 lb., and the water 

 evaporated nearly 7 j millions of 16. Upon the wagon-head boiler the 

 time occupied was 1291 hours, the coals consumed nearly 600,000 16., 

 and the water evaporated above 44 millions of 16." 



The quantity of water supplied to the boilers was accurately deter- 

 mined by means of a cistern "gauged by weighing 21 cvit. of water 

 into it, and marking the height of each cwt. upon a floating gauge- 

 rod ;" which is of course the same thing as if it had all been weighed. 



" The coals were actually iccighed, not measunS, into the stoke-hole, 

 and the surplus, if any, was also weighed at the end of every 12 

 hours'" 



The results of these experiments on boilers are contained in Table 

 No. v., in which are also given all the details of the experiments ; 

 and, from a comparison of columns 16 and 22, which show Me it'tighl 

 of fuel burned per square foot tif grate per hour, and the neight of rcatei 

 evaporated by one 16. of coals from 8u^, respectively, we should con- 

 clude the latter to be independent of the former, since there is not the 

 slightest correspondence to be perceived in the variations of the two 

 quantities, if these variations be observed throughout the whole series 

 of experiments ; but the author, by comparing only the six experi- 

 EQents upon all four Cornish boilers, and the one upon the wagon-head 

 boiler, when most perfectly clothed, found the evaporative effect of a 

 pound of coals to increase with the rate of combustion per square foot 

 of grate. He gives the follow ing table of the mean results of the six 

 experiments upon the Cornish boilers, three with quick, and three 

 with slow combustion. 



Quick. Slow. 



Pound of coals per hour - - - 342- 1S8. 



Cubic feet of water per hour - - 46-9 25-4 



Pounds of coals per square foot of grate per hour 4'682 2'59G 



Pounds of water evaporated per ft. of coal from 80° 8-524 8-426 



Ratio - - - - - 100 98-8 



In this comparison the advantage of increasing the rate of combus« 

 tion from 2-596 16. to 4-GS2 16. per square foot per hour, or a little 

 more than SO per cent, appears to be nearly 1^ per cent. But if this 

 advantage can with certainty be attributed to the more rapid combus- 

 tion, ought we not to expect the same advantage to accrue from a still 

 greater increase in the rate of combustion, with two or three of the 

 same boilers ? — This does not, however, appear to have been the case. 

 The mean rate of combustion in the 26 experiments upon 2, 3 and 4 

 cylindrical boilers was 5,01316. per square foot of grate per hour, and 

 the mean evaporation per 16. of coals, 8-224 tt>. of water from 80°. The 

 slowest rate of combustion was 2*475, with the 4 boilers, and the cor- 

 responding evaporation, 8*258 ft., or 0-41 per cent, above the mean ; 

 and the quickest rate of combustion, with two of the same boilers, was 

 8-708 lb. with an evaporation of only 8-082 lb. of water per lb. of coals, 

 which is 1'73 per cent, below the mean. The mean of the six highest 

 rates of combustion with the cylindrical boilers was 7-7171bT and the 

 corresponding mean evaporative effect of a pound of coals, 8-038 lb., 

 or 2-26 per cent, below the mean of all the 26 experiments upon Cor- 

 nish boilers. The rate of combustion under the wagon-head boiler 

 (when well clothed, as the comparison [would not otherwise be fair) 

 was 10-89 lb. per square foot of grate per hour, and the evaporative 

 effect of a pound of coals in that boiler under those circumstances, 

 8-301 lb. ; but the engine was only worked during the day time, whence 

 resulted a loss of effect equal to 1-78 per cent., so that the evapora- 

 tion per pound of coals, if the boiler had been worked continuously 

 night and day, as the cylindrical boilers were, would have amounted to 

 8-449 lb., or 2-74 per cent, more than the mean of the cylindrical 

 boilers, the rate of combustion being rather more than double. If, 

 Ijowever, Mr. Wicksteed had happened to make only one experiment 



with the cylindrical boilers (as he did witli the wagon-head boiler well 

 clothed), and that one had been the 2nd in the table, in which the rate 

 of combustion was equal to the mean of the 26 experiments, but the 

 evaporation 8-605 lb. per pound of coals, the advantage would have 

 appeared in favour of the cylindrical boilers with slow combustion. 

 It would seem, therefore, from these results, either that the propor- 

 tions of grate and heated surface to the quantity of coals burned per 

 hour exercise little or no influence on the evaporative economy of a 

 boiler, or that experience is not yet sufficient to justify any conclusions 

 on that head. However this may be, the facts here recorded are ex- 

 tremely valuable, inasnnich as they are the results of long continued 

 and carefully conducted experiments, of which we are made acquainted 

 with all the circumstances generally considered necessary to be known. 

 They seem to indicate that each experiment, in order to be conclusive, 

 ought to last as long, or nearly so, as all the experiments upon the 

 cylindrical boilers taken together, and that all the circumstances con- 

 nected with the management of the flres ought to be closely attended 

 to, some of which are not observed at all, such as the supply cf air t» 

 the furnace, and the temperature of the air in the chimney, if they 

 can be ascertained, even comparatively ; for it is very probable that 

 these circumstances varied much in the experiments under consider- 

 ation without its being perceived, and thus caused variations in the 

 evaporative results, which may be ascribed to other causes. The ex- 

 periments upon the wagon-head boiler appear, however, to prove very 

 clearly the great advantage of efficient clothing, since the evaporative 

 effect of a pound of coals increased invariably with the quantity of 

 clothing, the advantage of a well clothed boiler over the same boiler 

 entirely exposed being shown to be equal to 10-8 per cent, which pro- 

 duces so important a saving of fuel, that the practice of clothing boilers 

 cannot be too strongly recommended. 



We extract the following calculation made by Mr. Wicksteed to 

 show which kind of boiler is preferable in a commercial point of view. 



"One wagon-head boiler evaporated 54-5 cubic feet per hour, and 

 weighed 7i tons. Four cylindrical boilers evaporated 46-9 cubic feet 

 per hour (the most rapid evaporation), and weighed 48 tons. If 46*9 

 cubic feet required 48 tons of boiler, 54-5 cubic feet would require 

 5oi tons. 



£ s. d. 

 Cylindrical boilers, 654 tons at ^27 - 1498 10 

 Wagon-bead boilers, 7i tons at £27 - 195 15 



Difference 



- 1302 15 



"Supposing the boilers are worked 365 days, the whole 24 hours,the 

 coals consumed by the cylindrical will be equal to 1556 tons per annum, 

 and by the wagon-head boiler 1569 tons, the saving in favour of the 

 cylindrical boilers is equal to 13 tons of coals, which at 20s. is equal 

 to 13/. It would be useless to continue the comparison of the com- 

 mercial merits of the two classes of boilers farther." 



From the results of his experiments on the evaporative power of 

 various coals, the author has formed the following table, 



"SHOWIXG THE COMMERCIAL VALUE OF THE COALS. 



The price of small Newcastle coals evaporating 7-68 ft. of water per It. of 

 coals was, in 1S40, I4s. 6d. per ton m the Pool ; this price is taken as a 

 standard, and the value given is according to the evaporative power of the 

 different varieties. 



The best M'elsh 



Anthracite . . . - 



The best small Newcastle 



Average small Newcastle 



Average Welsh ... 



Coke from Gas-works 



Coke and Newcastle small J and -} 



AVelsh and Newcastle, mixed 4 and J - 



Derbyshire and small Newcastle, i and i 



Average large Newcastle 



Derbyshire 



Blythe ilain, Northumberland 



We have seen that Mr. Wicksteed's experiments upon Cornish and 

 wagon-head boilers do not establish any certain superiority of either 

 over the other in evaporative economy, although Mr. Parkes, in his 

 paper on Steam Boilers and Steam Engines, published in the 3rd 

 volume of the Transactions of the Institution of Civil Evgineers, states 

 the Cornish to be superior to the common wagon boiler by as much as 

 one-third. It is, however, to be remembered that this conclusion is 

 drawn from experiments of short duration compared to those made by 



3 C 2 



