Lead. Lead is only prepared on the large scale. It is usually extracted from galena, a natural sulphuret of lead, by roasting the ore in a reverberatory furnace, and afterwards smelting it along with coal and lime. Its specific gravity, in a state of absolute purity, is 11.38 to 11.44, but ordinary lead seldom exceeds 11.35. It melts at about 612° Fahr., and when very slowly cooled, crystallizes in octohedrons. It is malleable and ductile, but devoid of elasticity. Lead is not dissolved by muriatic, sulphuric, or the vegetable acids, unless by free contact with air, and then very slowly: but nitric acid rapidly oxidizes it, forming a solution of nitrate of lead. Pure water, put into a leaden vessel, and exposed to the air, soon corrodes it, and dissolves the newly-formed oxide; but river and spring water exert no such influence, the carbonates and sulphates in such water destroying its solvent power. Lead may be alloyed with most metals, except those which differ greatly from it in specific gravity and melting point. It has a strong affinity for gold and silver, and is therefore employed to separate those metals, by cupel-lation, from other metals and minerals.

3254. Cautions on the Use of Lead for Cisterns, etc.

3254. Cautions on the Use of Lead for Cisterns, etc.. Ordinary water, which abounds in mineral salts, may be safely kept in leaden cisterns; but distilled and rain water, and water that contains scarcely any saline matter, speedily corrode, and dissolve a portion of lead, when kept in vessels of that metal. When, however, leaden cisterns have iron or zinc fastenings or braces, a galvanic action is set up, the preservative power of saline matter ceases, and the water speedily becomes contaminated with lead. Water containing free carbonic acid also acts on lead; and this is the reason why the water of some; springs, kept in leaden cisterns, or raised by leaden pumps, possesses unwholesome proper- ties. Free carbonic acid is evolved during the fermentation or decay of vegetable matter, and hence the propriety of preventing the leaves of trees falling into water-cisterns formed of lead.

3255. To Test the Richness of Lead Ores

3255.    To Test the Richness of Lead Ores. Lead ores, or galena, may be tested in different ways. The wet way is as follows: Digest 100 grains of the ore in sufficient nitric acid diluted with a little water, apply heat to expel any excess of acid, and largely dilute the remainder with distilled water. Next add dilute hydrochloric acid, by drops, as long as it occasions a precipitate, and filter the whole, after being moderately heated, upon a small paper filter. Treat the filtered liquid with a stream of sulphuretted hydrogen; collect the black precipitate, wash it, and digest it in strong nitric acid; when entirely dissolved, precipitate the lead with sulphuric acid dropped in it, evaporate the precipitate to dryness, the excess of sulphuric acid being expelled by a rather strong heat applied towards the end. The dry mass should be washed, dried, and exposed to slight ignition in a porcelain crucible. The resulting dry sulphate is equal to .68 per cent, of its weight in lead.

3256. To Find the Percentage of Lead in Lead Ores

3256.    To Find the Percentage of Lead in Lead Ores. This can be done by applying the test in the wet way (see No. 3255 (To Test the Richness of Lead Ores)), and multiplying the weight of the product obtained in grains by .68. It may also be found in the dry way, as follows : Plunge a conical wrought iron crucible into a blast furnace, raised to as high a heat as possible ; when the crucible has become of a dull red heat, introduce into it 1000 grains galena (lead ore) reduced to powder, and stir it gently with a piece of stiff iron wire flattened at the end. This wire must never be suffered to get red hot. To prevent the ore from adhering, after 3 or 4 minutes, cover up the crucible; and when at a full cherry-red heat, add 2 or 3 spoonfuls of reducing flux (see No. 3464 (Flux for Reducing Lead Ore)), and bring to a full white heat; in 12 to 15 minutes, after having scraped down the scoria, etc., from the sides of the crucible, into the melted mass, the crucible should be removed from the fire, and the contents tilted into a small brass mould, observing to run out the metal free from scoria, by raking the latter back with a piece of green wood. The scoria is then reheated in the crucible with 1/2 spoonful of flux, and this second reduction added to the first. The weight in grains of the metal obtained, divided by 10, gives the percentage of metallic lead in the sample of ore.

3257. To Make a Lead Tree

3257.    To Make a Lead Tree. Dissolve 1 ounce sugar of lead (acetate of lead) in 11/2 pints distilled water; add a few drops of acetic acid; place the liquid in a clear white glass bottle and suspend a piece of zinc in it by means of a fine thread secured to the cork.