tools, for example, have only the small edge tempered that is used for doing the work, the remainder being left quite soft, whereas in many other cases the entire piece of steel is tempered equally throughout. The tempering of a chipping chisel will explain the former process. The point of the tool is first heated to a cherry-red colour, for some two or three inches, after which it is taken from the fire and put into water, in a vertical position, for about half that distance. At this stage a very common accident, called water-cracking often takes place. It is caused by the sudden change of temperature at the surface of the water, which may be greatly lessened by imparting a slight vertical motion to the tool. When quite cold, the point should be made bright with a piece of sand-stone, in order that the colours may be seen distinctly. If everything has been done carefully and rapidly, the point should appear white, gradually changing into yellow, straw-colour, purple, and blue. These colours will now move towards the point by conduction of the heat in the body of the chisel. When the proper colour, viz., one of the shades of purple - depending on the work the chisel has to be used for - has reached the point, it should be plunged immediately into water, which will complete the operation. A little practice, so as to get acquainted with the particular kind of steel under treatment, and the proper heat required, should ensure very good work. If the steel has to be tempered uniformly throughout, then the method is quite different, the whole piece being hardened and thereafter brought back to the desired colour by borrowed heat, metal bath or 'blazing-off' with oil as commonly used for springs. Steel may be welded with care, using borax as a flux, but the greatest caution is necessary to prevent overheating, which results in the partial destruction of the steel, by liberation of the carbon, A bright red heat should in every instance be avoided, but if overheated, the damage may be partially repaired by repeated heating, and hammering till cold.