NATURAL PHILOSOPHY. 



verse strains, is increased sixty per cent, by its continued exposure in 

 fusion." 



In most of the books which treat of the strength of cast iron, the resistance 

 which it opposes to certain strains, is given ; but little useful information can 

 be obtained in them respecting the difference of strength in different kinds of 

 cast iron. But as the density between the lower and higher grades of this 

 metal differs as 6.9 to 7.4 a difference of thirty-one pounds per cubic foot, 

 and as the tenacity of the metal has a relationship to its density, it was found 

 by these experiments that cast iron, having a density of 6.900, had only 

 a tenacity of 9000; while that having a density of 7.400, had a tenacity 

 of 45, 970. 



Castings of the greatest weight, according to their size, are by far the 

 strongest, and weighing them is a ready means of judging comparatively of 

 their strength. 



Some important facts were also developed in relation to the cooling of heavy 

 castings. At the Fort Pitt Iron Works, two eight-inch and two ten-inch 

 guns were cast, one of each in the common way, solid, and one of each with 

 a core on a tube of iron, through which water was made to circulate after 

 casting, to cool it from the interior, according to an invention of Lieutenant 

 Kodman. The solid eight-inch gun burst at the 73d discharge ; the hollow 

 cast one stood 1,500 discharges, and did not burst; the solid ten-inch cast 

 gun stood only 20 fires, while the hollow ten-inch gun stood 249. These guns 

 were cast of the same material, and at the same tune; the difference in favor 

 of the hollow cast guns is astonishing. This is attributed to the method of 

 cooling, it being supposed that in cooling, the solid guns contract entirely 

 from the outside, and that a strain is exerted upon the arrangement of the 

 particles of the metal in the same direction as the strain of the discharges. 

 In addition to these facts, Major Wade gives some additional information in 

 relation to the effect of time, after the castings are made, and before they are 

 used Eight-inch guns proved 30 days after being cast solid, stood but 72 

 charges ; a gun of the same bore, proved 34 days after being cast, stood 84 

 charges ; while one which was proved 100 days after being cast, stood 731 

 charges, and another, proved after being cast six years, stood 2,582 charges. 

 Major Wade accounts for this phenomenon hi cast iron, by supposing that the 

 particles strained in the cooling re-adjust themselves in the course of time to 

 their new position, and become free or nearly so. In regard to the necessity 

 of care in the selection of iron, Major Wade says, " What most demands 

 attention at present, is the ascertaining and prescribing the conditions to be 

 exacted of the raw material, and of its treatment up to, and exclusive of the 

 casting ; for if we do not make sure of obtaining a good quality of iron at the 

 time of its casting into the mould all else is useless, and worse than useless." 



So much for the experiments on cast iron. Those in relation to brass and 

 bronze castings, made at the works of the Ames Manufacturing Company, 

 near Springfield, Mass., are no less valuable and interesting. 



Brass founders have often noticed a remarkable difference in the color and 

 quality of castings made from the same molten mass of brass, and have been 

 puzzled to account for this. It is believed by many persons that in forming 



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