25G METALS 



refining, must consist in the removal of this carbon ana any remaining 

 impurities. This i$ done by buriring it out, and for this purpose the 

 poorer kinds of cast iron answer as well as the best. Formerly the 

 metal was melted three or four times, and then hammered w r ith a large 

 forging hammer to remove the scoria. In the next improvement, the 

 metal while in fusion was stirred for a while to effect the more com- 

 plete combustion of the carbon ; and in this way it gradually lost its fusi- 

 bility and became stiff enough for forging. This process is called pud- 

 dling. The metal passes first through one fusion as preparatory. It ia 

 next placed on plates in a furnace of the reverberatory kind, the metal 

 being loosely piled in the middle of the horizontal furnace ; 3£ cwt. is 

 an ordinary charge. The flame plays over it, and in half an hour it 

 begins to melt. The workmen now stir it about, occasionally dashing 

 in a scoopful of water. The metal gives off freely bubbles of gas, which 

 burn with a blue flame, (carbonic oxyd) ; in about twenty minutes the 

 whole falls to pieces like a coarse gravel, and a lurid flame appears over 

 it. The whole is still kept in motion and well heated, and soon it be- 

 gins to unite again, when it is separated into several lumps of the size 

 of three or four bricks. These masses as they assume a clotty consis- 

 tency (sometimes called " coming into nature,") are drawn from the 

 furnace and dolleyed or stamped into cakes with hammers. The plates 

 are thrown while hot into water, which renders them brittle ; they are 

 then broken into pieces, again placed together in the furnace, heated to 

 a welding heat, and finally forged under a ponderous hammer, moved by 

 machinery, into short thick bars called blooms. 100 parts of cast iron 

 yield about 63 of blooms. Some of the steps in this process are often 

 neglected in making the ordinary iron. 



It has been found that full 24 per cent, of the gas escaping from an 

 iron furnace is carbonic oxyd, and in the boshes this is the only gas 

 This gas has been used as fuel in the refining of the iron, and by this 

 means the whole expense of fuel for refining is saved. (See the Amer. 

 Jour. Sci., vols. i. and ii.,2d ser., where the theory of the blast furnace 

 is well explained.) 



The iron produced is said to be cold short if it is brittle when cold, 

 and this has been attributed to the presence of silicium. It is termed 

 red short when it becomes brittle on heating. 



Cast iron is also changed to malleable iron by covering castings with 

 powdered hematite or other oxyd of iron, and exposing to heat below 

 fusion. The carbon is removed by the oxygen of the oxyd. The scales 

 of oxyd thrown off in the forging of iron are much used. This process 

 was first introduced in 1804, and is one of great importance in the arts. 

 Malleable iron is also obtained directly from the ore by a single fusion 

 in what is called a Catalan forge. It has a rectangular crucible or basin 

 below the fire, about 18 inches by 21 in width and 1 7 inches deep. The 

 twier enters about 9£ inches above the bottom and receives the blast 

 from a water-blowing machine ; and it admits of a change of position 

 so as to give a change of direction to the blast as is required in the 



Describe the manufacture of wrought from cast iron. How is the 

 gas used in heating 1 What are cold short and red short iron ? What 

 other mode is there of rendering cast iron malleable ? Describe a mode 

 of obtaining malleable iron direct from the ore. 



