Dissolve four ounces of saleratus in one quart of water and boil the files in it for half an hour, wash and dry them. Have ready in a glass or stoneware vessel 1 quart of rain water to which 4 ounces of best sulphuric acid have been slowly added, keeping these proportions for any amount used. Immerse the files in this preparation, then wash them clean. Dry quickly and cover with a little sweet oil. Coarse files should remain in the diluted sulphuric acid for about twelve hours, though from six to eight hours are enough for fine ones. Files may be recut three times by this process, and the liquors may be used at different times if desired. R. B. Casey.
Schenectady, N. Y.
Brush the old files with a wire brush, put them in a tub, cover them with water and add 6 ounces of caustic soda per each 100 files. In about two hours brush them again. They will then be free of grease and metal. Then put them in a box, lined with sheet lead, on a wire stand made for the purpose, and in such a way that they will not touch one another. Cover them with a solution made of nitric acid and water, one pint of acid to each gallon of water. In 25 minutes remove them, wash them in water, brush them with a hair brush and put them back in the liquid to which one more pint of nitric acid to each gallon of water has been added. In about 50 minutes remove them again, brush them after washing them with water and put them back in the liquid to which has been added ½ pint of sulphuric acid per each gallon of water. In 15 minutes remove them; wash them first in water, then in concentrated lime water till all trace of the acid has disappeared. When dry they will have the appearance and cutting quality of new files. I used this method for rocutting old files long ago and found it O. K., and so can recommend it.
Los Angeles, Cal. J. M. Menegus.