Fig. 1431.

“Experiment No. 7.—To ascertain the amount of scaling which took place in heating and cooling under same conditions as Experiment No. 6, a wrought-iron plate was cut from the same piece as No. 6, thickness .74 in., planed on both surfaces and all edges to a form nearly rectangular, and to the dimensions given in [Fig. 1431].

“The only difference (except the very small difference in the dimensions) between this and [1430], was that the principal grain of the iron was in [1431] in the direction of the arrow, whereas in the other it was lengthwise of the plate.

“This piece was subjected to fifty heatings to redness and sudden coolings in water of ordinary temperature, as in the case of No. 6. The change in form was exactly the same in general character, but the contraction was not quite so great either in length or breadth; the increase in thickness, however, was proportionately greater, the volume (measured by displacement of water) after fifty heatings being 48.6 cubic inches, which is nearly the same as in No. 6 after the same number of heatings. The weight of the piece:—

Avoirdupois.
lbs.oz.dr.
Before heating141015
After fifty heatings13510
Difference115

“This represents a loss of 9.07 per cent. of the original weight by scaling, and upon the whole original surface (sides and edges) represents a thickness of .0284 of an inch for the fifty immersions, or .00057 of an inch for the thickness of the film lost at each immersion over the whole surface.

“Calculating the weight of No. 6 before and after experiment from the volumes and specific gravities, we find the following:—

Volume. Mean
specific
gravity.		 Weight of
cubic inch
water.		 Pounds.
Weight before heating should be53.08 × 7.64 × .036 = 14.599
„after„„48.72 × 7.562 × .036 = 13.262
Difference in weight1.337