Phosphorus has little effect upon the hot properties, but in the cold state makes the steel brittle and is of course highly undesirable although some writers have claimed that it adds to the tensile strength in about the same degree as carbon. SULPHUR. Sulphur has just the opposite effect of Phosphorus, and makes the steel crack while it is being hot worked, although after the metal is cold it seems to have no particular effect upon the physical properties. ELEMENTS WHICH HAVE BECOME ESPECIALLY ASSOCIATED WITH SPECIAL ALLOY STEELS. Such elements are:—Chromium, Tungsten, Molybdenum, Vanadium, Cobalt, Uranium, Titanium, Aluminum, etc. CHROMIUM. Chromium is an indispensable constituent in modern high speed steel, and does not make a poor high speed steel, even when used alone. The chief effect which chromium produces in high speed steels is undoubtedly that of “hardening”. However, chromium, like carbon, will produce brittleness, if added in too large quantities, although if kept down to between 2 to 5% it seems to allow the lowering of the carbon element, while at the same time maintaining the desired hardening effect, without causing undue brittleness. The great hardness in the face of an armor plate, and the great toughness in the back of the plate, also the superb properties in the projectile which attempts to pierce the plate, can all be induced in chromium steels to a degree unattainable by the use of any other single element. As a simple chromium steel the product may be used in five-ply plates for the manufacture of safes. These plates are made of five alternate layers, two of chrome steel and three of soft steel, and after having been hardened, offer resistance to the drilling tools employed by burglars. Hardened chromium rolls are manufactured for use in cold-rolling metals. Files, ball and roller-bearings are other noted products of this type of steel. It is the essential constituent of those steels which neither rust nor tarnish. TUNGSTEN. It was soon found that the composition of “self-hardening” steels was not the best one for high speed steels. Tungsten was discovered as an element which gave the steel properties of hardness and toughness at a red heat. After the peculiar heat treatment had been learned, and the presence of manganese or chromium in addition to the tungsten was shown to be unnecessary in appreciable amounts, it was found that more durable qualities could be obtained by increasing the percentage of tungsten, while at the same time the carbon element was greatly reduced.