Cut bones into parts 2-2.4 inches (5-6 cm) long. Cut heads of tube bones. Pour cold water into cut bones, bring quickly to a boil, reduce heat and simmer, skimming foam constantly. Boil beef bones for 4 hours, pork and mutton bones for 2-3 hours. To improve taste and smell, add carrot, onion and parsley root 30 minutes before the end of the cooking.