(2) Is wrought iron almost free from carbon. Heated particles thrown from wheel follow straight line. These become broader and more luminous some distance from their source of heat.
(3) Illustrates mild steel action. Small amount of carbon present causes a division or forking of the luminous streak.
(4) Shows the effect of increasing the carbon from 0.50 to 0.85 per cent in mild steel. The iron spark lines diminish: the forking of the luminous streak occurs more frequently, being subdivided by re-explosions from smaller particles.
(5) Is a piece of carbon tool steel. The iron lines are practically eliminated with the increase of the explosions and subdivisions, causing display of figures.
(6) Gives the spark of high-speed steel, containing in addition to 65 per cent carbon, other alloying elements, chiefly tungsten and chromium.
(7) Represents a manganese spark. (Occasionally found in cast iron.)
(8) Shows spark thrown from old grade of “Mushett” steel.
(9) Represents a magnet steel spark.
(67) Externally cast iron usually has some sand on its surface and its cross-section shows the grain to be fine, even, and to have a dull grayish color. The surface of malleable iron contains no sand and its grain is very fine, such as cast iron, but slightly darker in color. A very fine steel veneer is on all surfaces of malleable iron, which is much lighter in color. When the welding torch is applied to cast iron, no sparks are given off, but when applied to malleable iron a bright spark is thrown off which breaks in falling, showing that the outside material is steel. These sparks soon cease and the metal which is molten is covered by a heavy oxide or skin which recedes or draws away from the flame slightly, showing a very porous cast-iron interior. When brought in contact with the emery wheel steel sparks, which are very luminous and break in falling, are given off first in the case of malleable iron, but they soon change to the dull red spark of cast iron. When a chisel is applied to cast iron, the iron chips off; when applied to malleable iron the edge will curl up, then chip off when the cast iron is reached. The cross-section of cast steel shows a bright, coarse, silvery gray grain. When the torch is applied a distinctively steel spark which is luminous and breaks in falling is thrown off. When applied to the emery wheel steel sparks are thrown off; when the edge is chipped by a chisel it will curl up.
METHODS OF DISTINGUISHING METALS