349 
&eam Engine* 
I have lately begun, and shall pursue, a set of experi- 
ments, with the intention of regulating by this safety pis- 
ton, the quantity of admitted air to fire-grates, and to ef- 
fect, by that means, a new mode of regulating the fire, 
and the elasticity of steam in boilers, with less expendi- 
ture of fuel and of force than usual ; of which idea a hint 
is given in the work and place above mentioned. The 
result of these researches I shall at some future period do 
myself the honour of communicating to that society. 
Description of a new Boiler constructed with a view to the 
saving of Fuel By Benjam n Count of Rum- 
ford. Read at a Meeting of the first Class of the 
National Institute the 6th October^ 1 806, 
IT is well known that much is gained in the saving of 
fuel, when an extensive surface is given to that part of the 
boiler against which the flame strikes, but this advantage 
is often counterbalanced by great inconveniences. For a 
boiler of the form usually employed, having the bottom 
very much extended in proportion to its capacity, must 
necessarily present a great surface to the atmosphere, and 
the loss of heat, occasioned by the cold air coming in con- 
tact with this surface, may be more than sufficient to 
compensate the advantage derived from the extended 
surface of the bottom. And where the boiler is employ- 
ed for producing steam, as it is indispensably necessary 
that it should be of a thickness sufficient to resist the ex- 
temperature. But as in practice the cylinder is commonly ex- 
posed to a lower temperature than the piston, heated by the steam, 
a little increase of friction will take place by an increase of heat. 
To prevent the effect of this, I have found it useful to employ for 
the piston a metal of somewhat less expansive power than the cy- 
linder ; and the expansion of red copper being to that of brass 
i nearly as 10 to 1 1, I prefer making the piston of the former metal^ 
j when the cylinder is made of brass. 
I Voi. II. y V 
