ConJlruUhn of Furnaces. Saving of Fuel. ~ 165 



out, namely, that flame will act more efFeflually the greater the furface ; and this is propor- 

 tionally greateft in fmall furnaces : and, fecondly, that the cooling cSedc of the mafonry and 

 apparatus will be greater the greater its mafs ; and this alfo is proportionally greater in fmall 

 furnaces. The exaft fize to produce the greateft effedl is not eafy to be afcertained; but fup- 

 pofing this to be done, it will follow, as the Count has remarked to me, that in all eftablilh- 

 ments of confiderable magnitude, it will be better on this and many other accounts, to heat the 

 veflel by a number of fmaller fires, inftead of one large one. 



In the conftru6lion hereafter to be defcribed, the flame was at firft made to circulate round 

 the fides of the boiler ; but by fubfequent experiments, in which the circulation through thofe 

 fide flues was prevented (the hot vapour being ftill fufFered to enter them), it was found that 

 the efFefl: was accelerated by the fpeedier draft of the chimney, without any greater ex- 

 pence of fuel. 



In every furnace there feems to be a rate of working, at which the heat is more cheaply pro- 

 duced than at any other ; that is to fay, if there be too little fuel in the fire-place at once, the 

 procefs will be longer, and the lofs, by the conducSting power of the apparatus, more confiderable ; 

 if there be too much, the bufinefs will be performed more fpeedily, but at a greater expence, 

 chiefly from the efcape of heated vapour by the chimney. In fome cafes, it may be moft pro- 

 fitable to fave time ; in others, fuel. In the experiments, no. 31 and 32, it was found, that 

 to abridge the time one-third, there was an additional confumption of about one-eighth more 

 fuel. 



The progreflive improvements in the faving of fuel, as fummed up at page 12 1 of the eflay, 

 are very curious. With a common open fire, carefully managed, the precife refult was i.ii. 

 or lib. of fuel raifed i|^ lb. of water 180°. But in the experiment, no. 20. with the improved 

 fire-place and boiler, the refult was 20.1 ; or 20iybs of water, were boiled with lib. of 

 wood. So that it appears that the latter procefs was eighteen times more economical than the 

 former, and that feventeen parts out of eighteen of the fuel were confumed to no purpofc in the 

 firft experiment. With regard to the abfolute quantity of heat, the author deduces from the expe- 

 riments related in Dr. Crawford's treatife, that lib. of charcoal would caufe 57. 6 lbs. of water to 

 boil, if none of the heat was fufFered to efcape. And by Lavoifier's experiments, the quantities 

 of heat generated by equal weights of charcoal and dry oak are as 1089 to 600 ; and the Count 

 takes it to be nearly true, thal^equal weights of oak and of dry pine wood will afford equal quan- 

 tities of heat. Thefe pofitions afford the refult, that 31,74 lbs. of water would have been 

 brought from the freezing to the boiling heat by the combuftion of ilb. of his fuel. It follows, 

 therefore, that in the method of boiling over common open fire, nearly 28 parts out of 29 of the 

 heat are loft ; and that in the Count's experiments the abfolute lofs amounted to about one-third. 

 When the generation and lofs of fteam, the condu6ling power of the materials, and the quan- 

 tity of heat which muft neceffarily be fuffered to pafs up the chimney in order to produce a draft, 

 are confidered, it may be doubted whether the economy of fuel can be carried much farther. 



As the fuel of this country confifts of coal and coke, and not wood, it feems requifite to 

 ftate their comparative powers of affording heat by combuftion. The experiments of Lavoifier, 



Vol. III. — July 1799. Z quoted 



