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110                       METALLURGY   OF   CAST   IRON.
run down the runner and fill the pig beds through lower outlets, as at N and M. The dotted lines O O, in Figs. 24 and 25, are supposed to be level, and the angle of the main runner shows the incline from this level line.
A plan of the pattern is seen at T, Fig. 33. The recess at A is to assist the pigs being broken in two pieces when cold, and the formation as seen at B where the pig 'and sow join to make their separation at this point easy when breaking the iron after a cast. The same number of patterns are used as there are pigs to be moulded in a bed. A good method of forming these patterns is by a combination of sheet steel and wood. The steel which forms the outside, as shown by the heavy black line at P, is about -% inch thick, and formed to shape over an iron block before the wood is secured, as shown at V V and at S, the latter being a i % -inch piece of hard wood, secured by wood screws passing through the steel at the upper edge of every 4 inches into the wood board. To secure the pattern at its end, a %-inch rod passes clear through each end and is riveted. This method makes a very light pattern, and one which will last for years, and discounts a dozen times over the old plan of making all-wooden patterns, which are still used by some. The principle involved in the construction of these patterns is one the founder and patternmaker might often well utilize. The sow pattern is made of a continuous stick of timber, having one side at T faced with a sheet of J^-mcli steel, so as to prevent warping of the pattern. There is also a piece of iron % x 2 inches set in and screwed down on the top surface of the sow pattern, as seen at K, for the purpose of leveling; as constant friction of a level ons lifted the metal will have a good chance to is often surprising how rapidly, as about 75 per cent of the heat generated from the solid fuel is utilized. This is attained where one ton of coke will produce one ton of iron; and Sir........................    2,720     "