548 
l 
STEAM ENGINE. 
The vessel was half filled with distilled water which had 
been purged of air by boiling. The lid was then fixed on, 
having the third hole S, plugged up. A lamp being placed 
under the vessel, the water boiled, and the steam issued co¬ 
piously by the safety-valve. The thermometer stood at 213, 
and a barometer in the room at 29.9 inches. The weight 
was then put on the filth division. The thermometer imme¬ 
diately began to rise ; and when it was 220, the steam issued 
by the sides of the valve. The weight was removed to the 
10 th division ; but before the thermometer could be distinctly 
observed, the steam was issuing at the valve. The lamp was 
removed farther from the bottom of the vessel, that the pro¬ 
gress of heating might be more moderate; and when the 
steam ceased to issue from the valve, the thermometer was at 
227. The weight was now shifted to 15; and by gradually 
approaching the lamp, the steam again issued, and the ther¬ 
mometer was at 132J. This mode of trial was continued all 
the way to the 75th division of the scale. The experiments 
were then repeated in the contrary order; that is, the weight 
being suspended at the 75th division, and the steam issuing 
strongly at the valve, the lamp was withdrawn, and the mo¬ 
ment the steam ceased to come out, the thermometer was 
observed. The same was done at the 70th, 65th, division, 
&c. These experiments were several times repeated both 
ways; and the means of all the results for each division are 
expressed in the following table, where column 1st expresses 
the elasticity of the steam, being the sum of 29.9, and the 
division of the steelyard; column 2d expresses the tempera¬ 
ture of the steam corresponding to this elasticity. 
I. 
II. 
35 inches. 
219° 
40 
226 
45 
232 
50 
237 
55 
242 
60 
247 
65 
251 
70 
255 
75 
259 
80 
263 
85 
267 
90 
270J 
95 
274y 
100 
278 
105 
281 
A very different process was necessary for ascertaining the 
elasticity of the steam in lower temperatures, and conse¬ 
quently under smaller pressures than that of the atmosphere. 
The glass syphon S G F, was now fixed into its hole in the 
lid of the digester. The water was made to boil smartly for 
some time, and the steam issued copiously both at the valve 
and at the syphon. The lower end of the syphon was now 
immersed into a broad saucer of mercury, and the lamp in¬ 
stantly removed, and every thing was allowed to grow cold. 
By this the steam was gradually condensed, and the mercury 
rose in the syphon, without sensibly sinking in the saucer. 
The valve and all the joints were smeared with a thick 
clammy cement, composed of oil, tallow, and rosin, which 
effectually prevented all ingress of air. The weather was 
clear and frosty, and the barometer standing at 29.84, and 
the thermometer in the vessel at 42°. The mercury in the 
syphon stood at 29.7, or somewhat higher, thus showing a 
very complete condensation. The whole vessel was sur¬ 
rounded with pounded ice, of the temperature 32". This 
made no sensible change in the height of the mercury. A 
mark was now made at the surface of the mercury. One 
observer was stationed at the thermometer, with instructions 
to call out as the thermometer reached the divisions 42, 47, 
52, 57, and so on by every five degrees till it should attain 
the boiling heat. Another observer noted the corresponding 
descents of the mercury by a scale of inches, which had its 
beginning placed at 29.84 from the surface of the mercury in 
the saucer. 
The pounded ice was now removed, and the lamp placed 
at a, considerable distance below the vessel, so as to warm its 
contents very slowly. These observations being very easily 
made, were several times repeated, and their mean results are 
set down in the following table: Only observe, that it was 
found difficult to note down the descents for every fifth de¬ 
gree, because they succeeded each other so fast. Every 10th 
was judged sufficient for establishing the law of variation. 
The first column of the table contains the temperature, and 
the second the descent (in inches) of the mercury from the 
mark 29.84 :— 
32° 
3 
40 
0.1 
50 
0.2 
60 
035 
70 
0.55 
80 
0.82 
90 
1.18 
100 
1.61 
110 
2.25 
120 
3.00 
130 
3.95 
140 
5.15 
150 
6.72 
160 
8 65 
170 
11.05 
180 
14.05 
190 
17.85 
200 
22.62 
210 
28.65 
Four or five numbers at the top of the column of elastici¬ 
ties are not so accurate as the others, because the mercury 
passed pretty quickly through these points. But the pro¬ 
gress was extremely regular through the remaining points; 
so that the elasticities corresponding to temperatures above 
70° may be considered as very accurately ascertained. 
Not being altogether satisfied with the method employed 
for measuring the elasticity in temperatures above that of 
boiling water, a better form of experiment was adopted. A 
glass tube was procured of the form represented in fig. 2, 
having a little cistern L, from the top and bottom of which 
proceeded the syphons K and M N. The cistern contained 
mercury, and the tube M N was of a slender bore, and was 
about six feet two inches long. The end K was firmly fixed 
in the third hole of the lid, and the long leg of the syphon 
was furnished with a scale of inches, and firmly fastened to 
an upright post. 
The lamp was now applied at such a distance from .the 
vessel as to warm it slowly, and make the water boil, the 
steam escaping for some time through the safety-valve. A 
heavy weight was then suspended on the steelyard ; such as 
it was known that the vessel would support, and at the same 
time, such as would not allow the steam to force the mer¬ 
cury out of the long tube. The thermometer began imme¬ 
diately to rise, as also the mercury in the tube M N; their cor¬ 
responding stations are marked in the following table:— 
Temperature. 
Elasticity. 
212 ° 
0.0 
220 
5.9 
230 
14.6 
240 
25.0 
250 
36.9 
260 
50.4 
270 
64.2 
280 
106.0 
This form of the experiment is much more susceptible 
of accuracy than the other, and the measures of elasticity- 
are more to be depended on. In repeating the experiment, 
they were found much more constant; whereas, in the former 
method, differences occurred of two inches and upwards. 
We may now connect the two sets of experiments into 
one table, by adding to the numbers in this last table the 
constant 
