Lagging of Steam-Pipes. 



the result is independent in any further 

 and E ; the equation in fact becomes 



1 1 . -234 

 „ -234 + -57 l 0g6 ^i9" 



5ft 



way of both k 



h + 



log< 



■57 Wft °-i9 



Thus it is unnecessary to know the absolute values of k and 

 E, though we shall discuss these later on. 



This theoretic equation is represented by the continuous 

 curve on fig. 3. It will be seen that it corresponds with a 

 fair amount of accuracy with the experimental values. 



Fig. 3. 



i-fc 



(0 



p 





 r 

 

 01 



p 





Theo-relSc Curve 

 Ex f>e.Ti mental Fbi 



nl"s O 



? 







U 



o / 

 o / 



\ 1° 



3 

 O 







L° 





o\ 











Ootev Radius^ 







1 cm 



z 



It was considered worth while to obtain the absolute values 

 of the emissivity and conductivity of the asbestos paper 

 employed. The former was obtained from the rate of cool- 

 ing of a thinly coated bar, the temperatures being read by 

 the thermoelectric potentiometer method. Plotting a curve 

 of temperatures against time, and finding graphically the 

 slope at the 100° point of the curve, the emissivity was cal- 

 culated from the slope and the dimensions of the bar. The 

 value so obtained was '000275. 



