Sulphur is another impurity and high sulphur is even a greater detriment to steel than phosphorus. High sulphur up to 0.09 per cent helps machining properties, but has a tendency to make the steel "hot short," i.e., subject to opening up cracks and seams at forging or rolling heats. Sulphur should never exceed 0.06 per cent nor phosphorus 0.08 per cent. Steel used for tool purposes should have as low phosphorus and sulphur contents as possible, not over 0.02 per cent. We can sum up the various factors something as follows for ready reference. The ingredient Its effect Iron The basis of steel Carbon The determinative Sulphur A strength sapper Phosphorus The weak link Oxygen A strength destroyer Manganese For strength Nickel For strength and toughness Tungsten Hardener and heat resister Chromium For resisting shocks Vanadium Purifier and fatigue resister Silicon Impurity and hardener Titanium Removes nitrogen and oxygen Molybdenum Hardener and heat resister Aluminum Kills or deoxidizes steel PROPERTIES OF ALLOY STEELS The following table shows the percentages of carbon, manganese, nickel, chromium and vanadium in typical steel alloys for engineering purposes. It also gives the elastic limit, tensile strength, elongation and reduction of area of the various alloys, all being given the same heat treatment with a drawing temperature of 1,100 deg.F. (600 deg.C.). The specimens were one inch rounds machined after heat treatment. Tungsten is not shown in the table because it is seldom used in engineering construction steels and then usually in combination with chromium. Tungsten is used principally for the magnets of magnetos, to some extent in the manufacture of hacksaws, and for special tool steels.