SECT. II.]
PROPERTIES OF STEAM.
83
9 q~r\ ) v = the volume at the temperature t'.
Rule. As the volume the vapour occupies is to the volume it would become
by expansion, so is the elastic force at the lower temperature to that at the
higher one.
Or,
. /459 + f \
' '459 + * /
459 + t'\
459 + V
Taking as an example M. Cagniard de la Tour’s experiments on ether, it is
stated that it was completely in a state of vapour at a lower degree; but the
differences do not indicate this to have taken place till it was 447°, and its force
was 68*8 atmospheres; required its force at 617°. In this case
459 + 617 v
459 + 447 X
68-8 = 81*7 atmospheres.
In the experiment he states it as 94 atmospheres, and undoubtedly in conse
quence of the vapour of mercury forming in the apparatus, (art. 107.) ; and a like
remark applies to all his experiments ; for our rule for the expansion rather
exceeds the truth than otherwise.
120. By reversing the process, we may find the volume steam will occupy
under any compressive force not exceeding 60 atmospheres, when its volume is
known for a given temperature and pressure. For example, at 60° its force being
30 inches of mercury, its volume is 1324 times its volume in water. 1 Now by
increasing its temperature to the degree t' its volume would be,
1 The volume of any vapour or gas at 60° and 30 in. is easily found from chemical tables con
taining their specific gravity, compared with air at that temperature and pressure; for air is 828
times the volume of an equal weight of water; consequently, the number 828 being multiplied
by the specific gravity of the liquid, and divided by the specific gravity of the vapour in question,
gives its proportion of volume to an unit of volume of the liquid.
Thus steam is of the specific gravity ‘625; and
828
•625
1324.
The following table may be found useful in similar calculations with various liquids.
Substance.
Specific gra
vity in liquid
state, water
being unity.
Specific gra
vity in vapour,
air being unity.
Volume of va
pour for one of
liquid at 60°
and 30 in.
Constant
number for
formula.
Volume at the
boiling point
of the liquid.
Boiling point.
...
Water
1-000
0-625
1324
76-5
1711
212°
Alcohol
•825
1-6133
423
24-5
476
173
Sulphuric ether
•632
2-586
203
11-7
220
104
Sulphuret of carbon
1-272
2-6447
398
23-0
440
116
Naphtha
•758
2-833
224
13-0
280
186
Oil of turpentine
•792
5013
130
7-5
193
314
Oil gas liquid
•85
2-7
260
15-0
337
186
From this table it appears that one volume of water produces more vapour than an equal volume
of any other substance in the list.