4108. Tests for the Presence of Lead in its Solutions

4108.    Tests for the Presence of Lead in its Solutions. The presence of lead in solutions may be recognized by the effects produced by the following reagents:

The addition of sulphuretted hydrogen, hydrosulphuret of ammonia, or the alkaline sulphurets, to a solution containing lead, give black precipitates, insoluble in cold dilute acids, alkalies, alkaline sulphurets, and cyanide of potassium.

Caustic potassa or soda gives a white precipitate, soluble in excess of the precipitant.

Ammonia throws down a white precipitate, insoluble in excess, from all the solutions of lead salts, except that of the acetate.

Dilute sulphuric acid, in excess, also solutions of the sulphates, give a white precipitate, insoluble in dilute nitric acid, but soluble in a solution of potassa.

Chromate of potassa gives a yellow precip-itate, whose soluble qualities are the same as that from sulphuric acid last mentioned.

Iodide of potassium gives a yellow precipitate, soluble in acetic acid, a solution of potassa, alcohol, and boiling water; from boiling water it is deposited in small, brilliant, golden-yellow scales, as the liquid cools. (See also Nos. 2694, etc..)

4109. To Prepare Chloride of Zinc

4109.    To Prepare Chloride of Zinc. Dilute 1 pint hydrochloric acid with 1 quart water, add to it 7 ounces zinc in small pieces; when the effervescence is nearly finished, apply heat until bubbles cease to be evolved; decant the clear and evaporate to dryness. Fuse the product in a lightly covered crucible, by a red heat; pour it out on a flat, smooth stone, and, when cold, break it into small pieces, and preserve it in a well-stoppered bottlc.

4110. Ammonio-Chloride of Zinc

4110. Ammonio-Chloride of Zinc. By dissolving 68 parts chloride of zinc and 54 parts sal-ammoniac, a crystallizable salt is formed, which dissolves oxides of copper and of iron, and is useful in tinning or zincing these metals.

4111. Chloride of Zinc

4111.    Chloride of Zinc. Dissolve 21/2 troy ounces zinc in small pieces, in sufficient muriatic acid; strain the solution, add 60 grains nitric acid, and evaporate to dryness. Dissolve the mass in 5 fluid ounces water, add 60 grains chalk, and let tho mixture stand for 24 hours; then filter, and evaporate to dryness. Lastly, fuse the dry mass, pour it out on a flat stone, and, when it has congealed, break tho mas3 in pieces and keep in a well-stoppered bottle. (Z7. S. Disp.)

4112. Precipitated Carbonate of Zinc

4112.   Precipitated Carbonate of Zinc. Take 12 troy ounces each sulphate of zinc and carbonate of soda; dissolve each separately in 4 pints water; mix the solutions and let tho powder subside; pour off tho liquid, wash tho precipitate with hot water until tho washings are nearly tasteless, and dry with a gentle heat. (U. S. Ph.)