Scald a granite-ware coffeepot. Beat egg slightly and dilute with one-half cup cold water, add to coffee and mix thoroughly. Turn into coffeepot and add boiling water, stir well. Place on range; let boil five minutes. If not boiled sufficiently, coffee will not be clear; if boiled too long, the tannic acid will be extracted, causing serious gastric trouble. Stuff the spout of pot with soft paper to prevent the escape of aroma. Stir down, pour off one cup to clear the spout of grounds, return to pot. Add remaining half-cup cold water to complete the clearing process. Place pot on back of range for ten minutes, where coffee will not boil. Serve immediately. If coffee must be kept longer, drain from the grounds and keep just below boiling point.