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until a condition of temperature equilibrium is obtained — that is, the 

 electrical input just compensates for the tliormal output — and a second, 

 and exactly similar pipe, be covered with a 'non-conducting' cover and 

 heated in the same niAiiner, it will be found that much less electrical 

 energy is needed to keep the covered pipe hot than is required by the 

 bare pipe. The difference represents the saving due to the use of the 

 covering." — Laboratory Notes, Massachusetts Institute of Technology. 



In accordance with the above plan, we are now vising for a lab- 

 oratory exercise for engineering students the apparatus shown in Fig. 1. 

 Two pieces of ordinary three-inch gas pipe of equal length (40 inches), 

 are closed by means of caps at both ends. They are mounted on an oaken 

 support, and separated by a g-inch oak board, which prevents one pipe 

 receiving heat from the other. Three short pipes are fitted into holes in 

 the upper cap extending through about an inch; one (B. Fig. 2), of 

 f-inch pipe, five inches long in the center, another (A), of ^-inch pipe, five 

 inches long, for the support of a thermometer, and a third (C). of §-inch 

 pipe, nine inches long on the opposite side of the center from the second, 

 for the lead wires of the heating coil. 



The heating coils (G), made of No. 16 advance wire, are wound on a 

 paper-insulated brass tube, which extends along the axis of the pipe. 

 Each turn of the coil is separated from the neighboring coil by a hemp 

 cord. The tube is held in position at the top by telescoping over the lower 

 end of the pipe which pierces the middle of the cap. At the lower end 

 it is held in position by a wooden frame (E), clamped rigidly around it 

 by means of screws. This frame also holds firmly the lower end of the 

 heating coil and the lower part of the paper insulation. A similar clamp 

 holds the upper end of the coil and insulation. 



The two pipes are covered alike at the ends by means of magnesia 

 covering one inch thick (D and F), leaving 36 inches of each one bare. 

 Brass collars having a flange extending out flush with the circumference 

 of the covering are clamped to the pipes and prevent the end covering from 

 slipping along the pipes. W:hen a test is to be made, a piece of pipe 

 covering of regulation length (36 in.) and suitable size, is placed on one 

 of the pipes, thus completely covering it, while the other one has an 

 equal length left bare. 



The tube (Fig. 3), upon which the heating coil is wound, acts also as 

 the cylinder for a puni]). by means of which the oil is stirred. It is J inch 



