When work on cast iron must proceed at the utmost pace, a jet of air, delivered to the chips with force enough to clear them off as fast as they are formed, enables the speed to be quickened, while, at the same time, the life of the cutter is lengthened.[18] [18] The foregoing pages on steel have been revised by Professor Bradley Stoughton, of the School of Mines, Columbia University, New York. He contributes at the end of this chapter a brief list of books for the reader who may wish to know something of the literature of iron and steel. Alloys for Electro-Magnets. In electrical art the alloy employed for electro-magnets should be permeable by magnetism fully and easily, otherwise dynamos and motors will waste energy as their magnetism is constantly gained, lost, or reversed. Once more the experimenter is Mr. Robert A. Hadfield of Sheffield, who produces an excellent alloy by uniting iron with 2.75 per cent. silicon, .08 per cent. manganese, .03 per cent. sulphur, .03 per cent. phosphorus. This alloy is improved by being heated to between 900° and 1100° C., followed by quick cooling; then being reheated to between 700° to 800° C., and cooled very slowly. Iron is largely used as an electrical conductor, so that it is well to know how its conductivity is affected by ordinary admixtures. In experiments with sixty-eight specimens, Professor W. F. Barrett alloyed iron separately with carbon, aluminium, silicon, chromium, manganese, nickel, cobalt, and tungsten. In every case there was a loss of conductivity, and usually in a degree proportioned to the atomic weight of the added ingredient. Between one element and another there was often a wide disparity of effect. For example, in admixtures, each of one per cent., tungsten increased the resistance of a conductor by two per cent., while aluminium did seven-fold as much harm. Magnetic Alloys of Non-Magnetic Ingredients.