Each bed of iron when cast is obviously in the form of a huge comb and to render it merchantable this comb requires to be broken apart, and almost universally in foundry work the individual pigs require to be broken in two. This labor was in earlier days performed exclusively by hand and still is in many cases. There are two ways of breaking, hot and cold; the former requires the less labor but is the hotter and the more disagreeable. It is done by catching the iron at the temperature immediately below solidification, when it still has very little strength, and breaking the pig from the sow by the use of a crowbar applied under the junction of the two. The men wear clogs with wooden soles an inch thick, kept soaked in water when not in use, which are strapped to their shoes. A good deal of dust arises from the disturbance of the sand, while the radiation from the pig beds is very great in spite of the fact that a thin layer of sand is sprinkled over them, which cuts the heat down very greatly.

In the South, where the conditions of atmospheric heat and humidity are relatively bad, the custom has arisen of allowing the men to break the iron cold. The beds are watered down as soon as they are cooled below the point where sudden chilling affects the fracture and appearance of the iron, the men then go on the beds with heavy sledges and crowbars and break the iron from the sow and break the individual pigs in two. This requires more labor and so is more expensive, but the work is more endurable for the men.

When the iron is cast in chills it is watered down and as soon as it has solidified the men work on it in pairs. One takes a short crowbar in each hand and pries up the point of the pig where its contraction has shortened it up so as to leave a gap of about half an inch between it and the chill. This man puts a heavy upward strain on this point with his hand bars, while his partner strikes a hard blow at the junction of the pig and the sow with an extra heavy sledge. This breaks the pig off from the sow and the latter is pried up and broken into two or three pieces by sledging, after the pigs are all broken from it. Casting the iron into chills instead of casting it in sand exercises a profound influence on its structure, particularly with irons low in silicon such as are required for the basic open-hearth process and for which chills are used. If the iron be 1 per cent. or over in silicon its fracture is markedly different, when cast in chills, from that produced by casting in sand; it is much closer and finer grained, but the general nature of the iron is not much affected. But when the silicon gets down below 0.8 per cent., particularly if the sulphur be above 0.05 per cent., the iron begins to chill, and if the silicon drops still further it becomes perfectly white, very hard and excessively brittle. This is an advantage for steel-making purposes since it has been proven that chilled iron melts more easily than the same iron not chilled, and therefore this facilitates melting down the iron in the open-hearth furnace.

But for general foundry work iron cast in chills has only been introduced very slowly and after much missionary work among foun-drymen who have very largely learned to judge the iron by its fracture and general appearance, an iron of open grain with large crystals being in general much superior from the foundryman's point of view for general work to a close-grained iron with small crystals. Therefore casting in chills converted good iron into bad from the foundryman's point of view, and if the silicon was a trifle low, converted a really useful iron into one which foundrymen would not consent to use under any circumstances because it was "white".

This condition is gradually wearing away as foundrymen come to use analysis instead of fracture to judge the quality of their iron, but many merchant furnaces supplying the foundry trade still continue to cast their iron in sand, and will for years to come.

Fig. 212. Interior of cast house with pile of "combs" from pig beds. Crane lifting one pig bed out of sand.