All the precipitates of lead salts, with the exception of the sulphide, are soluble in fixed alkalies, in ammonium acetate, ammonium tartrate, and ammonium citrate. It is possible to determine the presence of lead in a large volume without evaporating down the whole bulk of fluid. By this means liquid containing lead is treated with sulphide of copper, sulphide of mercury, or baryta-water. Meillère states that he has detected the presence of as small a quantity as 1 milligramme of lead in 1,000 c.c. of water in this manner without evaporating the liquid. Where lead is in organic combination, as is the case in the urine of persons suffering from lead poisoning, it is not decomposed by hydrogen sulphide, and the method is therefore not applicable in such cases, but is useful in water examination. =Electrolytic Reactions.=--Solutions of lead are easily electrolyzed, and give a precipitate of lead at the cathode; simultaneously the peroxide is produced at the anode, and the reaction is acid. In nitric acid solutions Riche pointed out that the whole of the lead is carried to the anode, and this is the reaction made use of in the determination of lead present in the urine (see p. 172). The presence of copper in an electrolyte regulates the precipitation of lead oxide, copper alone being deposited at the cathode, and at the same time the presence of a small quantity of copper promotes the destruction of organic materials. REFERENCES. [1] PLINY: lxxxiii., 11, N.c.v. [2] STOCKHUSEN: De Litharg. Fumo, etc. Goslar, 1656. [3] TRONCHIN: De Colica Pictonum. 1758. [4] JOHN HUNTER: Observations of Diseases of the Army in Jamaica. London, 1788. [5] MEILLÈRE, G.: Le Saturnisme. Paris, 1903. [6] BISSERIE: Bull. Soc. Pharmacol. May, 1900. [7] HOUSTON: Local Government Board Annual Report, 1901-02, supplement, vol. ii. CHAPTER II ÆTIOLOGY Lead poisoning of industrial origin rarely occurs in the acute form. Practically all cases coming under the notice of either appointed surgeons, certifying surgeons, or even in the wards of general hospitals, are of the subacute or chronic type. There is no reason to suppose that lead compounds are used more frequently by the workers in lead industries as abortifacients than by other persons. The compounds of lead which are responsible for poisoning in industrial processes are for the most part the hydrated carbonate, or white lead, and the oxides of lead, whilst a comparatively small number of cases owe their origin to compounds, such as chromates and chlorides.