(1) Have the water lukewarm, and a little soapsuds in it. Bring the mandrel to a cherry - red, catch by the end in tongs, and be sure to dip slowly and vertically to the bottom of the tub. If moved sideways, it will camber. (2) The risk of cracking steel when hardening is much reduced by surrounding the article, when in the fire, by shreds of leather, bone, etc, or by covering it with prussiate of potash as soon as it gets to a dull red heat; then it may be heated to the proper temperature for hardening. It is a very difficult thing to prevent the spindle from being bent and distorted. If hardened in water, it is almost sure to "warp," and, if the mandrel is a large one, it is not easy to harden it in oil. If it is of moderate size, heat it as above, with leather, etc, and at a good red heat; immerse it vertically in a mixture of oil and tallow.