CHAPTER XVIL CONSTANT AND CHANGEABLE METALLOIDS IN MAKING IRON. If, in making iron, all the metalloids remained fairly constant, not varying in their percentage one cast from another, we could obtain a uniform product and have no such thing as different grades of iron from like mixtures of ore, fuel, and flux. But this condition does not exist; instead, we find that a furnace, at the present state of advancement, seldom makes two casts of iron exactly alike in analysis or grade from the same mixtures of like ores, fuels, and fluxes. The elements that vary the most and effect the greatest change in the grade or the carbons of iron are silicon and sulphur. A furnaceman can be most particular and have all conditions alike as far as lies in his power, but for all this he may have some casts which will differ widely in silicon and sulphur contents, especially when making iron over 1.50 silicon and in all grades during very hot weather. It is true there will be changes in the total carbon, manganese, and phosphorus, but these rarely cause radical changes in the grade of an iron coming from like mixtures. Some experiences on this latter point are related in Chapter XVIII., page 136. It is to be remembered that the author is not claiming- that manganese and phosphoruss to evolve ideas which may favor the inauguration of new practices that to-day might seem absurd and impracticable.