Unlike puddling furnace and open-hearth no burning out of the silicon, manganese and carbon is desired, though, of course, some occurs and has to be allowed for in calculating the mixture. The intention is simply to melt together with the least possible loss a mixture of such materials as will give the average final composition which long experience has shown to give the proper qualities to the finished product. Charges usually are of certain percentages of pig iron with not too much phosphorus, sprues from previous melts, more or less good malleable iron scrap and small amounts of steel scrap. These are melted down as quickly as possible. Occasionally the slag which accumulates is skimmed off and, after rabbling, test plugs are poured from the fractures of which the composition of the iron is judged. When the silicon content is deemed proper or has been adjusted through longer action of the flame if too high or addition of more silicon in the form of a high silicon alloy if too low, the iron is tapped, provided it is hot enough. Malleable iron is largely used for very small castings. These require very hot and fluid metal. So, even if it is of proper composition, the metal must be held in the furnace until it is of a high enough temperature to pour properly. Through prolonged and strong heating the iron may easily become oxidized or “burnt” and much skill is necessary for proper operation of the furnace. After tapping, the iron must be got into the molds with the least possible delay. As has been mentioned with former processes the melting of iron in contact with coke or coal results in more or less contamination with sulphur. For this reason cupola malleable has considerably higher sulphur than has malleable cast iron made in the air furnace. Cupola and air furnace each has certain advantages and certain disadvantages. While strength and elongation are somewhat greater in air furnace than in cupola malleable, both anneal well and give materials which are satisfactory for the purposes for which they are intended. Cupola metal has an advantage in that the temperature and the composition can be closely maintained the same throughout the heat, perhaps more so than with the air furnace. With the latter the metal at the top of the bath is hotter than that underneath, and, through action of the flame and air, silicon is somewhat lowered before all of the heat can be poured, especially with air furnaces of large size. The metal can easily be “burnt” unless extreme care is taken. In the cupola we can get very hot iron continuously so that it is unnecessary to prolong the heat with the danger of burning that occurs with the air furnace.