_Another Mode._—Make a solution by dissolving in 10 gallons of soft water, salt, 1 peck; oil vitriol, ½ pint; saltpetre, ½ lb.; prussiate of potash, ¼ lb., and cyanide of potassium, ½ lb. Heat the iron to cherry-red and plunge at once into the cold solution. This makes cast iron hard enough to cut glass, and is the method usually resorted to for hardening the cheap cast-iron glass cutters, now so common on the market. _To Soften Wrought Iron._—Heat the iron with a slow blast to a dark-red, then pour upon the burning coals half a pint of fluoric acid. Keep up the blast gently, without increasing the degree of heat, until all sign of the acid has disappeared, then lay out the iron to cool gradually of itself. _Alloy for Filling Holes in Iron._—Melt together nine parts lead, two parts antimony and one part bismuth. Pour into the hole while in a molten state, or drive in while the iron is somewhat hot. This alloy possesses the peculiarity of expanding as it cools, consequently the plug tightens as its temperature falls. _To Harden Iron for Polishing._—Pulverize and dissolve the following-named articles in one quart of boiling water: blue vitriol, 1 ounce; borax, 1 ounce; prussiate of potash, 1 ounce; charcoal, 1 ounce, and common salt, ½ pint. Add to this 1 gallon raw linseed oil. Having finished up the article ready for polishing, heat it to a cherry-red, and plunge into the mixture; a rapid stirring of the mixture should be going on at the time when the plunge is made. This preparation hardens the iron to such a degree that it takes and retains polish almost equal to the best of steel. CHAPTER XI. ON WORKING IN STEEL. _Hand-Forging Steel._—In the main this does not differ materially from the same work in iron. Special care must be exercised to have the fire clear of sulphur, hence charcoal is the best fuel to use. In cases where the use of bituminous coal cannot be avoided, the fire should be blowed up for several minutes before putting in the steel, to drive off the sulphur. Steel to be forged should not be heated to so high a degree as is employed for iron; for ordinary light work a little above a cherry-red is enough. It does not work well under a high degree of heat; and, to make amends, it can be worked much colder than iron. In fact, it is always best to hammer it with light blows until the red color of the heat has entirely disappeared, as this improves its texture by adding decidedly to the closeness of the grain.