MIXTURES FOR LIGHT MACHINERY, ETC. 283
chilling quality than others, often due to some special peculiarity of the ores from which the iron was made, or working of the furnace, and which might often be explained were analyses carried beyond determining the regular five elements. However, it is often well for a founder, in starting to make light or stove plate castings, to purchase pig iron (after the methods described in page 200) from the furnaces that can show their irons are being successfully used by other light work or stove plate foundries.
If any yard or foreign scrap iron is used, care should be taken to have it clean and free as possible from rust or oxide of iron; also, no burnt iron should be used, as such will greatly cause mixtures to give hard iron in light work. (Facts treated further in pages 295 to 297.) The best test for softness in light work castings generally lies in the castings themselves, as almost every light casting if not of a sufficiently soft character is readily told by means of a file, grindstone, or chisel. If light castings crack, it is generally evidence of the iron being too high in sulphur or phosphorus, or too low or high in silicon, which latter can be told readily by an examination of the fracture, as if they are too low in silicon the edges of the casting will show a greater chill than from an excessive use of silicon. Then again, the latter will give a very brittle body, while the former will be of a stronger character. It is to be remembered that there is a limit to the use of silicon in affording softness, and that it can make very brittle castings, as shown on page 209.ossessing more of a.50 to 3.00