310 On the Rapid Production of Steam. 
stated at 8 atmospheres ; so that by adding the 523 derived from 
the over-heated metal we should have no less than 603 atmospheres 
or 906 Ibs. to. the square inch for the resulting elasticity. ~ This is 
upon the assumption that steam obeys the same law in regard to its 
relative bulk and elasticity, as that which governs atmospheric air. 
Bat if it do not follow that law, there is no probability whatever that 
the pressure would be less than in the direct ratio of the density. | i 
Before proceeding to the detail of experiments on other metals, 
think it proper to present the following series of results, in which my 
main object was to ascertain, accurately, the rapidity of cooling of © 
iron from incandescence down to 212°, taking into consideration the 
temperature of the water, both at the beginning and end of the ex- 
periment, its weight in some cases, and the relation, in all cases, be- 
tween the weight of metal and the amount of its generating surface. 
These experiments were performed in an apparatus similar to that 
described in my former communication, but furnished with an at- 
- tached thermometer to mark with accuracy the temperatures attained. 
The result, as will be seen, is, that the times approximate to an in- 
verse proportion to the generating surface. 'This proportion will not 
be found to obtain, where part of the heat was employed in raisiDg 
temperature, and a part in generating steam. The time demanded ; 
for cooling a given mass of metal from redness to 212°, by the latter 
process, must be greater than by the former, both because the tem- 
perature of the liquid, which is to receive heat, is greater, and the 
difference between it and the metal less, and because the surface of 
the iron is momentarily denuded of water and prevented from acting 
by a constant and uniform communication. The temperature, 4 
few instances, was calculated by multiplying the weight of water by 
the number of degrees through which it was heated, and dividing the 
product by the weight of metal multiplied into its specific heat. - 
the quotient was, of course, added 212°, the temperature at which 
the metal was withdrawn after every trial. 
4 
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