The urine is evaporated down to the consistency of gruel, and the fæces mixed in distilled water to a like consistency. They are then treated by the wet method, as given above. The filtrate after cooling is placed in a glass cell, the bottom of which consists of a sheet of vegetable parchment; the cell is immersed to such a depth in a deeper cell, containing distilled water acidulated with a few drops of sulphuric acid, that the liquids in the inner and outer cells stand at the same level. A piece of platinum-foil enclosing a surface of about 50 square centimetres, constituting the kathode, was submerged in the liquid contained in the inner cell, a similar piece of platinum-foil, constituting the anode, being immersed in the outer cell. The pieces of foil are so placed as to be opposite each other, separated by the parchment diaphragm. A current, 3 or 4 volts, is then passed through for from six to eight hours, after which the foil is removed from the inner cell and gently washed and dried. The metallic lead is dissolved off the foil with dilute nitric acid aided by heat, and after driving off most of the free acid the solution is decomposed with dilute sulphuric acid with an equal volume of alcohol added. It is then set aside for twenty-four hours. The precipitate of lead sulphate is washed with water containing 12 per cent. of alcohol, until all the free acid is removed; it is then separated by decantation, ignited, and weighed. The amount of lead is calculated from the weight of the sulphate; 100 parts of sulphate are equal to 68·319 parts of metallic lead. Whether the moist or the dry process is used, the residue after the primary filtration should be tested for lead, which may be present as sulphate and remain undissolved. If the original substance contains lead as sulphate, the salt should be dissolved with heat in an aqueous solution of ammonium tartrate to which a little free ammonia has been added, then precipitated with sulphuretted hydrogen (100 parts of lead sulphide equal 86·61 parts of metallic lead). It is better, however, to convert the sulphide into sulphate by treating it with nitric and subsequently sulphuric acid, after which it is ignited, weighed, and the amount of the metal calculated by the lead sulphate factor. Having obtained the substance by decomposing the organic matter, two methods of estimation may be made use of: (1) Colorimetric; (2) gravimetric.