On the Density of Steam at all Temperatures. 201 
long. The globe was enclosed in a copper boiler, forming a steam- 
bath by which it could be uniformly heated. The copper steam- 
bath was prolonged downwards by a glass tube enclosing the globe 
stem. To heat this tube uniformly with the steam-bath, an outer 
oil-bath of blown glass was employed, heated like the copper bath by 
gas jets. ‘The temperatures were observed by thermometers exposed 
naked in the steam, but corrected for pressure. The two mercury 
columns forming the saturation gauge were formed in the globe stem, 
and between this and the outer glass tube; so long as the steam in 
the glass globe continued in a state of saturation, the inner column 
in the globe stem remained stationary, at nearly the same level as 
that in the outer tube. But when, in raising the temperature, the 
whole of the water in the globe had been evaporated and the steam 
had become superheated, the pressure no longer balanced that in 
the outer steam-bath, and, in consequence, the column in the globe 
stem rose, and that in the outer tube fell, the difference of level 
forming a measure of the expansion of the steam. Observations of 
the levels of the columns were made by means of a cathetometer at 
different temperatures, up to 10° or 20° above the saturation point ; 
and the maximum temperature of saturation was, for reasons deve- 
loped by the experiments, deduced from a point at which the steam 
was decidedly superheated. 
The results of the experiments, which in the paper are given in 
detail, show that the density of saturated steam at all temperatures, 
above as well as below 212°, is invariably greater than that derived 
from the gaseous laws. 
The apparatus for the experiments at pressures below that of the 
atmosphere was considerably modified ; and the condition of the steam 
was determined by comparing the column which it supported with 
that of a barometer. The results of these experiments, reduced in 
the same way, are extremely consistent. 7 
As the authors propose to extend their experiments to steam of a 
very high pressure, and to institute a distinct series on the law of 
expansion of superheated steam, they have not at present given any 
elaborate generalizations of their results. The following formule, 
however, represent the relations of specific volume and pressure of 
saturated steam, as determined in their experiments, with much 
exactness. 
Let V be the specific volume of saturated steam, at the pressure P, 
measured by a column of mercury in inches ; then 
49513 
V=25°62 eRe ead e e e e e 2. 
wu ee p- me 
49513 : 
— el 4 e.  8 ° e e e e Se 
wn at SUN ses 
In regard to the rate of expansion of superheated steam, the ex- 
periments distinctly show that, for temperatures within about ten 
degrees of the saturation point, the rate of expansion greatly exceeds 
that of air, whereas at higher temperatures the rate of expansion 
approaches very near that of air. Thus in experiment 6, in which 
the maximum temperature of saturation is 174°°92, the coefficient of 
