with a View to the Saving of Fuel. 355 



And as in the case where the boiler is constructed on 

 a great scale, the seven tubes that descend from the bot- 

 tom of the boiler into the fire may be made of cast-iron, 

 whilst the body of the boiler is composed of sheet-iron 

 or sheet-copper, it is certain that a boiler of this kind, 

 sufficiently large for a steam-engine, a dyeing-house, or 

 a spirit-distillery, would cost much less than a boiler of 

 the usual form, of equal surface and power. 



But in all cases where it is required to produce a great 

 quantity of steam, it will be always preferable to em- 

 ploy several boilers of a middling size, placed beside 

 each other, and heated each by a separate fire, instead 

 of using one large boiler heated by one fire. 



I have shown in my Sixth Essay, on the management 

 of fire and the economy of fuel, that beyond a certain 

 limit there is no advantage derived from augmenting 

 the capacity of a boiler. 



It will be perceived that the boiler which I have the 

 honour of presenting to this Society is of a form fit for 

 being placed in a portative furnace, and it was actually 

 intended for that purpose. 



Its furnace, which is made of bricks, with a circular 

 iron grate of 6 inches in diameter, is built in the inside 

 of a cylinder of sheet-iron, 17 inches in diameter and 3 

 feet high, and can be easily transported from place to 

 place by two men. 



This cylinder of sheet-iron, which is divided into 

 two parts, in order to facilitate the construction of the 

 masonry, weighs only forty-six pounds. The masonry 

 weighs about a hundred and fifty pounds, and the boiler 

 twenty-two pounds. 



In order to form an estimate of the advantage which 

 the particular form of this boiler gives it in accelerating 



