The base of all steels is Iron. It goes without saying that this element should be obtained in the best and purest state possible. Probably the best “base” iron comes largely from Sweden, which country seems to have produced the highest quality of iron on the market today. CARBON. Carbon has already been discussed under Carbon Steels, although, of course, its importance in Alloy Steels must not be under-estimated. The proportion of carbon aimed at in high speed tool steels is about 0.65%, which in simple steel would not be enough to give the maximum hardness, even if the steel were heated above the critical point and quenched in water, and still less so when the steel is cooled as slowly as these steels are in their treatment. This shows that the carbon element acts in a different way from what it does in simple carbon steels as previously discussed. MANGANESE. Manganese Steel is a typical self-hardening steel and so, obviously, is any steel which is in the austenitic condition at atmospheric temperatures, that is to say, whose critical temperature is below atmospheric temperature. Thus, self-hardening steels are non-magnetic. Because of its low-yield point, manganese steel does not give satisfaction in many lines, for which otherwise it might be eminently fitted. Manganese used in =small= quantities (.30% to 1.50%) will produce certain desired effects. Under these conditions it acts as a purifier. And when added in the form of Ferro Manganese to a heat of steel it unites with the oxygen and transforms it to slag as oxide of manganese. There is also good reason for believing that manganese prevents the coarse crystallization, which impurities such as Phosphorus and Sulphur would otherwise produce. Five per cent to 14% manganese renders the steel non-magnetic as well as a poor conductor of electricity. SILICON. The dividing line between silicon-treated steels and silicon-alloy steels is not clearly defined, but the latter are used for several important purposes. Such steel has been used in springs of the leaf type for automobiles and other vehicles, the silicon being considered to add slightly to the toughness of the springs. However, the most important use of steels of this type is probably in the manufacture of electrical machinery. It is possible to produce a silicon-alloy steel which has not only a greater magnetic permeability than the purest iron, but also, a high electrical resistance. Its hysteresis is, of course, low, this property always accompanying a high permeability. It therefore is a very valuable material for use in electro-magnets, and in electric generating machinery, is the most efficient material known. In silicon-treated steels, the silicon is used somewhat as a scavenger, although it also produces results somewhat similar to manganese. PHOSPHORUS.