So far from being simply iron, pig contains a large and variable proportion of other matters amounting often to 10 or 12 per cent.; and these confer upon it its fusibility. The principal one is carbon, which is found in the metal partly in the state of chemical combination with it, and partly in the form of small crystals similar to those of graphite or plumbago, disseminated through the mass. When there is a comparatively small proportion of the carbon combined with the iron, the substance is grey, and it can be filed or drilled or turned in a lathe. In white cast iron the combined carbon predominates, or is sometimes accompanied by scarcely any graphitic carbon; it is brittle and so very hard that a file makes no impression. It fuses at a lower temperature than the other varieties. A third kind is the _mottled_ cast iron, which shows a large coarse grain when broken, and distinct points of separate graphite particles; it is tougher than the others, and therefore when cannon were made of cast iron this variety was preferred. The following table giving the percentage composition of four samples of crude cast iron will show their diversities. ┌─────────────────────────────────┬────────┬────────┬────────┬────────┐ │ │ White.│ White.│Mottled.│ Grey.│ ├─────────────────────────────────┼────────┼────────┼────────┼────────┤ │Iron │ 88·81│ 89·304│ 93·29│ 90·376│ │Combined carbon │ 4·94│ 2·457│ 2·78│ 1·021│ │Graphite, or uncombined carbon │ ...│ 0·871│ 1·99│ 2·641│ │Silicon │ 0·75│ 1·124│ 0·71│ 3·061│ │Sulphur │ trace│ 2·516│ trace│ 1·139│ │Phosphorus │ 0·12│ 0·913│ 1·23│ 0·928│ │Manganese │ 5·38│ 2·815│ trace│ 0·834│ └─────────────────────────────────┴────────┴────────┴────────┴────────┘ The reader will observe that the last item in the table above is a substance that he has not yet made the acquaintance of, namely, _manganese_. This is a metal which in many of its chemical relations much resembles iron, and ferruginous ores usually contain a greater or less proportion of it. Manganese is of great importance in the manufacture of steel, as we shall presently see; but as a separate metal it has no application, and is obtainable in the metallic state with much difficulty. One of its oxides has however very extensive applications in the chemical arts, and others form acid radicles, which in combination with potash or soda give rise to useful products. The well-known “Condy’s fluid” is a solution of one of these.