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.