JUDGING OK AND TESTING MOLTEN IRON. 309
being poured he can often greatly control, and hence the advantage of practice in this factor causes study to train the eye, which very soon becomes expert in deciding the best moment at which to pour a mould. A like study of the molten character, combined with the temperature in a fluid state, may enable the moulder to judge as well in one case as the other, and this should be practiced more than it is, as no moulder or founder can tell when a knowledge of the former would not be as valuable as the latter.
Judging the grade of metal by its appearance in a fluid state is often done by experienced founders, and with a little study and observation the following description may often enable the inexperienced to soon become proficient in judging molten metal: A No. i or high graphite soft iron * will generally present a lively vibration of different colors having the appearance of coming up from below the surface, forming an oxidized crust. This crust has the appearance of struggling to break away from alloys, which do not take kindly to being associated with a grey or soft iron. When No. i iron is slowly cooling down from a high temperature to a low one, it will often be unable to hold all its carbon in a combined state. What cannot be retained will gradually rise to the surface as graphite in the form of a scum or kish, and in the latter state will float away in the air, often covering everything near at hand with thin flakes of shining material, looking like silver lead or plumbago. This can properly be called pure carbon freed from the metal. About blast furnaces, this latter phenomenon can often be seen, sometimes so active that the employes will be covered with "kish," making them look
*This refers to iron possessing from 2.50 to 3.00 of silicon. For results of higher silicon, see next paragraph.ron, Ferrochrom.