TK AXSVl-.KSK, CRl'SHING, IMPACT AND SMOCK TKSTS. 441
bridge found that shocks or light blows delivered on lest bars increased their strength, and therefore illustrate the benefits to be derived by the gradual increase of severity in shocks to strengthen castings, such as guns which are subjected to great, strains from sudden jars or blows to the metal comprising their bodies. They also show wherein many castings long iu use can have their durability increased, becoming really better than new castings.
These tests were made by means of twelve companion test bars that had been moulded in one flask and cast with the same gate and ladle of iron. Six. of these test bars were subjected to shocks by reason of tumbling in a "tumbling barrel,'1 and in other cases the shocks were transmitted to the test bars by means of tapping them on their ends with a hand hammer. The six bars not receiving shocks in any manner were invariably found the weakest. The bars receiving the shocks were shown by a large number of tests made by Mr, Outerbridge to have been increased in strength from ten to (iftern per cent, and the largest gain, in a few instances, was found to be about 19 percent, The bars tested were one and one-eighth ineh round, and also square bars of one inch section, both fifteen inches long, Mr. < hiterbridge says the crucial test was in subjecting six bars to 3,000 taps each with a hand hammer upon one end only of each bar, The tumbling barrel process of giving shocks to bars continued for about four hours. The publication of Mr, < hsterbridge's discoveries by trade papers has led many founders to experiment in testing his deductions, and all have found them to be true, some oven exceeding the strength obtained by Mr. < hiterbridge.ts, Mr. Outer- t.2 grammes on the diamond. Three estra weights, I, are used when necessary. Tlniy are each of the same weight as II. Uc-nee, with one weight, scale division m eorre:,ponds to m y^rammes on the diamond, with two weights i«> corresponds to '/o grammes,with thr<*e weights to -\n ^nimmes, and \«-ith tour weights to ,|o grammes, the other scale division:, in Volume XXIII. of the .*