5. _In the cases 2, 3, 4, if the precipitate be heated to redness, in contact with an alkaline carbonate; and after dissolving out the carbonate, it be redissolved in nitric acid; then sulphuretted hydrogen will form a dark cloud with the solution._ In these experiments it is necessary that the acid used to redissolve the precipitate be not in excess; if it should so happen, the excess must be saturated, before the test is applied. It is better to use so little, that some precipitate may remain undissolved. The nitric acid, used in these experiments, should be perfectly pure; and the sulphuretted hydrogen test should be recently prepared by saturating distilled water with the gas. (_b_) _Sulphate of soda, or potass._ This test will produce a white precipitate in water, containing one hundred-thousandth of its weight of lead; and is considered by _Dr. Thomson_ as the most unequivocal reagent of that metal which we possess. “The precipitate is a fine dense powder, which speedily falls to the bottom, and is not re-dissolved by nitric acid; no other precipitate can be confounded with it, except _sulphate of baryta_, and there is no chance of the presence of baryta in solution in water.”[391] (_c_) _Muriate of soda._ One of the methods of analysis proposed by _Dr. Lambe_, consists in precipitating the lead by common salt; but as the _muriate of lead_ is partly soluble in water, this test cannot be applied to small portions of suspected water. The precipitate must, therefore, be collected from two or three gallons, and heated to redness with twice its weight of carbonate of soda. The alkaline carbonate is then to be dissolved out, and nitric acid added, in order to saturate any superfluity; the _sulphuretted hydrogen_ test will then produce its indication. (_d_) _Reduction of the metal._ This is undoubtedly the most satisfactory of all the tests; and, except the trouble of collecting a large quantity of precipitate, is not embarrassed with any difficulty. The precipitate may be mixed with its own weight of alkaline carbonate, and exposed either with, or without, the addition of a small proportion of charcoal, to a heat sufficient to melt the alkali. On breaking the crucible, a small globule of lead will be found reduced at the bottom. The precipitate from about fifty gallons of water yielded _Dr. Lambe_ about two grains of lead.