
MECHANICAL ACTION OF HEAT. 165 
Section I].—Or REAL AND APPARENT SPECIFIC HEAT, ESPECIALLY IN THE STATE 
oF Prerrect Gas. 
(9.) The apparent specific heat of a given substance is found by adding to the 
real specific heat (or the heat which retains its form in producing an elevation of 
one degree of temperature in unity of weight) that additional heat which disap- 
pears in producing changes of volume and of molecular arrangement, and which 
is determined by reversing the sign of Q’ in equation 6 of Section I. (so as to 
transform it from heat evolved to heat absorbed), and taking its ¢ota/ differential 
coefficient with respect to the temperature. Hence, denoting total apparent spe- 
cific heat by K,— 
d.Q@ dQ dQ@ dQ av 


d 
Ces iden adn. ds. dv as 
1 3kM adV({1 aU dU 
=cam (opt — (3; (v7 ~ay) ~ ae) } O® 
Another mode of expressing this coefficient is the following :— 
: 2h 
Denote the ratio 32M PY N, 
and the real specific heat by & - . (14) 
Sitart 
~~ CaMN 
Then 

Ka {1+N (r-«) (ZG -y) -7") } as, 
The value of 3 is to be determined from the conditions of each particular 
case; so that each substance may have a variety of apparent specific heats, accord- 
ing to the manner in which the volume varies with the temperature. 
If the volume is not permitted to vary, so that _ = 0, there is obtained the 
_ following result, being the apparent specific heat at constant volume :— 
£= ohn -e-08) 
= (1-N (7-52) Res gle) 
(10.) When the substance under consideration is a perfect gas, it has already 
aU k dU 
been stated (Eq. 7), that 7-=—- a.7_7 
of weight is directly as the absolute temperature and inversely as the pressure, 
= 0; and because the volume of unity 
“FT ee Oe eek oe 
