On the Production of Steam from heated Iron. 71 
Art. IX.—Observations and Experiments on the variable rapidity 
of action, between water and hot iron; by Watter R. Jounson, 
Professor of Mechanics and Natural Philosophy in the Franklin 
Institute, Philadelphia. 
Tue several series of experiments heretofore detailed, in relation 
to the actual guantity of vapor yielded by red hot metal, and to the 
time employed in producing it, have furnished some of the data for 
calculating the effect of overheating a steam boiler and immediately 
furnishing it with water. It is evident, that even with the same tem- 
perature in the metal, certain circumstances may exist at one time 
which shall modify the result exhibited at another. ‘The tenth ex- 
periment in the fourth series,* in which 60 ounces of metal continued 
red for 82 seconds, beneath the surface of boiling water, and after- 
wards oce ipied 46 seconds in parting with the excess of heat above 
212° Which then remained, might possibly lead to the inference, that 
the quantity of heat disengaged in the former part of the operation 
Was at least twice as great as that which was given out in the latter. 
This would imply that the temperature, (omitting difference in spe- 
cific heat,) had been at first three times as much. above 212°. aaa 
Was at the moment when redness disappeared. But the whole of the 
fourth series, as well indeed as all the other seriés heretofore given, 
had manifested in the performance of the experiments, a muc re 
vigorous action subsequent to the disappearance of redness, than be- 
fore that period. It was therefore necessary, in order to obtain some 
degree of clearness on this head, to perform several courses, each 
“onsisting of a number of series of experiments. 
The general fact that red hot metal repels water, or at least does 
Not appear to exercise upon it any contiguous attraction, has long 
been familiar, The smith who plunges a piece of iron, at a white 
heat, mato his trough, sometimes sees with astonishment that scarcely 
Y ‘gitation of the liquid occurs for the first few seconds; and he 
ioe that this is not due to the coldness of the walet requiring 
seta eated up to boiling temperature, before it can . - 
elie Consequent upon the formation of steam; for by plunging 
: Piece of metal at a black heat into the same liquid, the ac- 
0 becomes immediately and distinctly perceptible. 
. A €n water is sprinkled upon a stone plate, even below redness, 
Na sc often observed to roll, apparently with little or no adhe- 
2 0m side to side, until slowly dissipated, or until they at length 
“See Vol. XX, p. 311, of this Journal. 
