235 



At 50% efficiency 14 x 10" B. T. U. are used in pipes at a cost of 

 $0.00. 



Cost of covering per 1,000 square feet at 25 cents per square foot, is 

 $250.00 ; interest 10% = $25.00. 



Total $275.00. 



123 X 10' -^ 14 X 10''=87.9 tons of coal required. 



87.9 X G = $527.40 loss per 1,000 feet per year. 



$527.40 — $275.00 == $252.40 saving for tlie first year for a pipe cov- 

 ering of 53% efficiency. 



Physical Laboratonj of Purdue TJnivcrsity, 

 Lafayette, Ind. 



