METAL SURFACES AND LIQUIDS IN CONTACT WITH THEM. 77 
and the jackets. The water in each cod being raised to the same temperature, 
To say, the scale reading was taken. The initial temperature of the water flowing- 
through the pipe was then set to a given value, say hs fde temperature of the jacket 
water being regulated so that the scale reading remained the same as before. When 
the final temperature of the water flowing through the pipe became steady, its 
value was taken. The temperatures of the pipe and jacket water were then again 
brought to the common value they had initially, and the scale reading again taken. 
If this agreed with the first reading, the experiment was taken as correct; if not, it 
was rejected and another made. 
The observations would be as follows :— 
Experiment 1, —'Water, 148 grins, per second. 
(a.) Measurement of Surface Temperature ;— 
Temperatui’e of iacket water = 47-8° I 
7 ocale reading, d'O/ centmis. 
nine .. = 47 8 J 
pipe ,, = 47'8' 
(b.) Measurement of Heat transmitted :— 
Initial temperature of water in pipe = 17-08'’. 
„ „ „ jacket = 07-60°. 
Final ., ,, pipe = 2445°. 
,, „ „ jacket = 61-10°. 
(c.) Clieching Surface Temperature : — 
Temperature of jacket water = 47-9° | 
pipe 
47- 
Scale I’eacling, 6-56 centims. 
Results of the Experiments, 
Tq = temperature of the inner surface of the pipe in degrees Centigrade. 
t = mean temperature of the water in the pipe at any cross section. 
V = velocity of the water through the pipe in centims. per second. 
p = pressure of the water. 
r — radius of the pipe in centims. 
L = length of the pipe in centims. 
Then, for a small element of the internal surface of the pipe = ^irr dl, we may 
w rite, for the case of transmission of heat from metal to water, 
Heat transmitted = c/H, 
= K , ^TTvdl (f) (Tf), t, (Tq — i). p . . r), 
where K and the function (f) are to be determined by experiment. 
From the description of the apparatus given above, it will be seen that the effect 
