On chemistry applied to the arts

F.Crace Calvert
1865 Journal of the Franklin Institute  
portions of oxide are carried into these joints, and it is at any rate certain that iron gives way easiest at these places. This points to the great value of really homogeneous plates, such as those of cast steel, in which homogeneity has been obtained by the only known means of fusion. The remarkahle diminution of elasticity and of tenacity caused by the combination of the red-hot iron with sulphur ; the absence of all elasticity and tenacity in the oxides of iron, show that, even if a flue do
more » ... , even if a flue do not at once collapse, or a shell explode, through getting red-hot, the boiler is more or less injured every time it gets overheated. A defective circulation, by permitting such a temperature as to drive the water off the plate, would soon lead to local injury. Particular spots in externally fired cylindrical boilers are sometimes, as is stated by Mr. L. Fletcher, of Manchester, thus affected, and in an apparently mysterious way. A new boiler in which a heap of rags were accidently forgotten, had the spot burnt out in a few days,* doubtless through the resulting defective circulation and its consequences. The plates just above the fire of internal flues also suffer in this manner. It is perhaps possible that turned joints, secured by bolts, and allowing an occasional reversing, or rather rotating, of the ring, might, in some eases, be here of service. At any rate, universal experience proves that the thicker the plate the easier does it get red-hot ; and these chemical facts also point to the desirability of a minimum of thickness. In fact, the wearing away of the plates through these causes, if mechanically strong against pressure, often gets arrested at a certain thickness. In Germany and France, some of the best manufacturers still make the plate over the fire of, for instance, inside flues, slightly thicker than anywhere else; but the combined chemical and mechanical actions of the heated fuel cause most wear and tear in a thick plate, and thus justify American practice in this respect. In that country, fire-box plates of good charcoal iron are made only ~¢ or ~ of an inch thick, and with stays four inches apart, give good results under nearly 150 lbs. steam pressure. (To be continued.)
doi:10.1016/0016-0032(65)90447-3 fatcat:xys43skuhnbnpaewehtspkikie