rans: IN; V. AC. nace. = M0 Dee. 19, 
in which ¢ represents the quantity of heat in units of heat per second, 
and ¢ the specific heat of air at constant pressure (¢ = 0,238.) 
All of the above formulas are well known. The following are 
believed to be new: 
The quantity of heat imparted to the air may also be represented 
by ¢’= Oe in which is the quantity of heat imparted per 
ae 
second, and as from the nature of the problem 9 = ¢’ we have 
Sees Sale 
= gee ee aD 
Sere —"L) 
a rg ee (WSF 3600 1 aD 
combining this equation with (8) we have— 
bi ee) V'2 
Siti = 5 = XE 12 
‘i 3600 20 H. i (2) 
V2 Wc 
d = 4, 
an PO ee (TT) (13) 
3600 
This expression gives the total heating surface in the pipes in terms 
of the velocity, the height of the flue, the weight of air discharged per 
second, and the absolute temperature of the external air. 
If we substitute for V’ its value in terms of V, the actual velocity, 
we have— 
a= 2.7 AGT) \ See 
3600 | 
and others WD MVavAs 
pi Ke OVS Dea Ts 
| 2p Bee (ee 7.) 
3600 
(15) 
another expression for 5S’. 
These two expressions exhibit the laws of the movement of the air, 
giving the quantity of heating surface required under any special con- 
ditions of area and height of flue, temperature of external air, and 
velocity of discharge. 
The constant (7) may be found approximately from the experiments 
of Mr. C. B. Richards, made at Colts Arms Co., of Hartford. The 
constant A depends upon the frictional resistance which the air 
encounters in its passage into and through the flues. The velocity V 
may be assumed, and should not be greater than four or five feet per 
second, The smaller the velocity and the larger the flues, the less will 
be the required heating surface, and the greater the economy of the 
apparatus for ventilation, 
