As a rule the prognosis of cases of lead poisoning occurring in industrial conditions is more favourable when colic is a marked feature than when it is absent, and there is no doubt that the prognosis in cases of industrial lead poisoning at the present time is more favourable than it was before the introduction of exhaust ventilation and general medical supervision--a fact no doubt to be explained by the relative decrease in the amount of lead absorbed. REFERENCES. [1] GOADBY, K. W.: Journ. of Hygiene, vol. ix., 1909. [2] HUNTER, JOHN: Observations of Diseases of the Army in Jamaica. London, 1788. [3] DRISSOLE AND TANQUEREL: Meillère’s Le Saturnisme, p. 164. [4] HOFFMANN: Journ. de Méd., October, 1750. [5] WEILL AND DUPLANT: Gazette des Hôpitaux, lxxix., 796, 1902. [6] BRIQUET: Bull. Thérap., Août, 1857. [7] PEYROW: Thèse de Paris, 1891. [8] STEVENS: Bulletin of Bureau of Labour, U.S.A., No. 95, p. 138, 1911. [9] ZINN: Berl. Klin. Woch., Nr. 50, 1899. [10] SERAFINI: Le Morgagni, No. 11, 1884. CHAPTER XII PREVENTIVE MEASURES AGAINST LEAD POISONING =Amount of Lead Fume and Dust in the Atmosphere Breathed.=--Lead fuses at 325° C. and boils at between 1450° and 1,600° C. It is volatile when heated to a cherry-red colour--about 550° C. Experiments[A] carried out in the laboratory of a lead smelting works in London to determine the temperature at which leady fumes rise from the surface of open baths of molten lead, showed that unless pure lead is heated to about 500° C., and at the same time stirred, no appreciable fume comes off, and that from lead, at the same temperature, under ordinary working conditions, little or no lead in the form of oxide passes into the air. From lead that has been unrefined or which contains zinc--that is, lead in the earlier stages of its manufacture (in the reverberatory furnace)--leady fume was not given off at temperatures less than 760° C. even when stirred, because at a temperature of 600° C. the surface of the molten metal became covered with fluid slag, which will not allow any oxide to be given off. Impurities such as tin or antimony prevent the oxidation of molten lead at lower temperatures, and give it a bright, shiny colour. When heated to about 600° C., these impurities form a slag on the surface of the lead containing antimoniates and stannates of lead, which do not evolve lead fumes unless heated to temperatures never likely to be reached in open lead pots. The reason why molten refined lead can give off lead fume more readily than those named is because the oxide formed on the surface is a dry powder and not in the form of slag. Hence, when the bath is stirred, some of the dry oxide is broken up and may rise into the air. When a bath of molten lead is not stirred at all, it can be heated to over 740° C. without finding oxide in the air aspirated--a temperature not obtained under ordinary working conditions.