454 
SECOND REPORT — 1832 . 
the most likely source of error ; for though Erman* has shown 
that a very minute admixture of a saline substance would cause 
an important difference in the temperature of maximum den¬ 
sity, we cannot suppose such experimenters to employ water 
that had not been several times distilled. 
Mr. Crichton f of Glasgow, by employing a thermometer tube 
with a large bulb filled with water, and allowing for the expan¬ 
sion of the glass, has more recently arrived at a determination 
agreeing very nearly with those of Muncke and Stampfer. The 
true point of maximum density he fixes at 38°*97 Fahr.; con¬ 
sequently that at which water acquires the same absolute mag¬ 
nitude as at 32°, is 45° * 94. 
Steam. —Mr. Johnson, of Philadelphia, has published the 
results of a series of experiments on the influence of tempera¬ 
ture and the powers of different metals in the generation of 
steam. He finds that more steam is generated in a given time 
by immersing in boiling water a mass of iron at a red heat, just 
visible in daylight, than by the same mass raised to a white 
heat. The steam generated bears a direct relation to the 
weight of the metal, being about one pound of steam for every 
nine pounds of iron. In comparing cast iron with malleable, 
he found that cast iron, raised to the same temperature, gene¬ 
rates more than wrought iron, being about one pound of steam 
for every eight pounds and a quarter of iron J. 
The former of these observations in regard to iron at a white 
heat corresponds with that of Leidenfrost, of the mobility and 
permanence of a drop of water on a very hot plate of iron ; and 
of Perkins, that an aperture in the side of a cylinder, which, at 
low temperatures, permits the passage of a jet of stream, ceases 
to do so when the cylinder is raised to very high temperatures. 
They call to mind also Pouillet’s observation, that water might 
be kept for a quarter of an hour in a platinum crucible, heated 
to w T hiteness, without sensible diminution. 
Ice .—Osann § has determined the specific gravity of ice at 
32° Fahr., and found, as a mean of ten weighings, of which the 
extremes were 0*9352 and 0*9198, the true specific gravity 
— 0*9268. It floated on oil of turpentine whose density at 32° 
was 0*9313, so that the specific gravity of the ice by this test 
cannot exceed 0*93. 
Per sulphuretted hydrogen .—The bisulphuret of hydrogen, 
the hydrosulphurous (hydrothionige) acid of the German che¬ 
mists, acts the part of an acid in the salts formerly called sul- 
* Poggendorf’s Ann. xii. 466. 
t Silliman’s Journal xix. p. 292. 
f Trans. Roy. Soc. Ed'inb. 
§ Kastner’s Archie, i. p. 95. 
