176 MR W. J. M. RANKINE ON THE 
The weight of one volume of water at 41 centigrade being taken as unity, 
that of half a volume of oxygen at 0° centigrade, under the pressure of one atmo- 
sphere, according to the experiments of M. REGNAULT, is 0:000714900 
That of one volume of hydrogen, . ; - . 0:000089578 
The sum being : 3 : ‘ : - 0:000804478 
374-6 
The reciprocal of this sum being multiplied by 1364166 the ratio of 
2746 — 
dilatation of a perfect gas from 0° to 100° centigrade) the result gives, for the 
volume of steam of saturation at 100° centigrade as compared with that of water at 
4°] : : : ; : 1695:72 
And for its density, : ; 000058972 
The agreement of those results with the known volume and density of steam 
is sufficiently close to shew, that at pressures less than one atmosphere, it may be 
regarded as a gas sensibly perfect; from which it may be concluded, that in the 
absence of more precise data, the errors arising from treating it as a perfect gas 
at such higher pressures as occur in practice, will not be of much importance. 
Representing, then, by v the volume of unity of weight of water at 4-1 cen- 
tigrade, that of unity of weight of steam at any pressure and temperature will be 
given by the formula 
_ 1696 v@ ee 
Vv (7) ?p 

(38.) 
zw representing the number of units of weight per unit of area in the pressure of 
one atmosphere, and (7) the absolute temperature at which the pressure of satura- 
tion is one atmosphere; being for the centigrade scale 374 °6, and for Fahren- 
heit’s scale 674-28. 
The mechanical action of unity of weight of steam at the temperature 7 and 
pressure P, during its entrance into a cylinder, before it is permitted to expand, 
is represented by the product of its pressure and volume, or by 


(39.) 
The coefficient aoe represents a certain depth of fall per degree of abso- 
lute temperature, and is the same with the coefficient — already referred to. 
By taking the following values of the factors :— 
v=0-016 cubic foot per pound avoirdupois, 
@=2117 pounds ayoirdupois per square foot, 
we find this coefficient to be 
153°35 feet=46'74 métres per centigrade degree, } 
85:19 feet per degree of Fahrenheit ; ) 

