KFKKCT OF KXPANSION ON SIIKINKAUK, KTC. 40^
throe thirty-seconds of an ineh of the short-arm lever-movement, I. e., of aetual extension of the bar); and consequently, the test bar, 48 inehes long as poured, \va,s elongated in solidification to 48-.^ inches, and then contracted in cooling to 47JZ inehes, its final length at atmospheric temperature.
The eloek shown at I, Fig. 78, with its face-plate, R. can be set independently, with a single recording-lever, to receive on the revolving face expansion and contraction curves from one end of the bar only, or it can be supported, as shown in Pigs. 76 and 77, so as to record curves in connection with the records made on the stationary or sliding- face-board, A.
The whole apparatus is of wood, except the fulcrum bars, I', Pigs. 76, 77, and 78, the casting-pin, >S, Pig. 75, and the pin-holding plates, K, Pig. 76. By a study of these levers in Pig". 79 it will he seen that a little pressure on the spring" side at B will instantly release the casting-pin seen at K, The :vi" casting-pins seen at. vS, Pig. 7«X, and in position at K, Fig', 79, arc. m:ule tapering, so that they can be' readily mov<kd from a test-bar and used again. They cause the levers to record sensitively any movements due* to expansion <>r contract ion after the bars arc poured. At the left of Fig. 79 is seen the form of pattern used for moulding the test bars. The projection at A is cast on, as shown, so as to insure equal action in recording* tin* expansion and contraction at. each end of the bar. At f> is a recess, which gives guide to mala,1 the same in the mould, so that in pouring the bars lt open-sand," the metal will ** flow off" at this point when it comes tt> that level, and thereby insure all burs being1 east eioselv to the same thickness.of ^