of it, pour a little very dilute sulphuric acid upon the sulphuret, so as not to wet the mouth of the decanter, and suspend the writing by means of the glass stopper, within the decanter. By an attention to the paper, the writing will become visible by degrees, as the sulphuretted hydrogen gas rises from the bottom of the vessel.

Experiment 21. In like manner add sulphuretted hydrogen to a solution of lead, and a deep brown precipitate will be occasioned. This is an effectual mode of detecting this and some other pernicious metals.

Experiment 22. If phosphorus be dropped into melted lead, they will unite, and form phosphuret of lead; or,

Experiment 23. If a mixture of equal parts of filings of lead and glacial acid of phosphorus be fused in a crucible, with one-eighth part of powdered charcoal, a button of phosphuret of lead will be formed. This phosphuret is composed of about 12 parts of phosphorus and 88 of lead.

Experiment 24. If three parts of lead be melted in an iron ladle, and one part of sulphur added, the two will unite into a sulphuret of lead, or artificial galena. We have the common sulphuret of lead, which contains about 14 per cent. of sulphur, and the super sulphuret composed of 25 per cent. of sulphur.

With respect to the uses made of lead in former times, the Romans sheathed the bottoms of their ships with this metal, fastened with nails made with bronze. During the first century, lead at Rome was twentyfour times as dear as it is now; whereas tin was only eight times its present price. Ceruse, or white lead, was in great use by the Roman ladies as a cosmetic. According to Bishop Watson, Plautus introduced a waiting woman who refused to give her mistress either ceruse, or rouge, because, forsooth, in the true spirit of a flattering Abigail, she thought her quite handsome enough without them. The use of lead, in imparting a saccharine taste to acid wines, was known to the ancients. Pliny mentions, that the Greeks and Romans proved the quality of their wines by dipping a plate of

M

lead in them. The practice of hiding the defects of wines by the use of lead, is happily abolished; its presence may be known in several ways.t

Lead has also been used to take off the rancidity of oils. Vats of lead have been used in some cyder countries, which have produced incalculable mischief.

The manufacture of lead into sheets is performed by suffering the melted metal to run out of a box through a long horizontal slip upon a table prepared for the purpose, while the box is drawn by appropriate ropes and pulleys along the table, leaving the melted lead behind it in the desired form to congeal. There is also a large consumption of lead in making shot.f

Lead is capable of combining with most of the metals, by different processes; as, with gold, platinum, silver, mercury, copper, iron and tin. The ley pewter, as well as the tin foil, of the English, is often nothing more than the alloy of tin and lead. Of the other alloys, but little is known.

Experiment 25. Mix two parts of fine powdered red oxyd of lead with one of common salt in a stone mortar, and form the two substances into a paste, with a little water, adding more occasionally as the mixture becomes dry.

The soda of the common salt becomes disengaged, and the muriatic acid unites with the oxyd of lead. Wash off the soda, dry the white mass, and fuse it in a crucible, it will form the beautiful and durable pigment called patent or mineral yellow.

The decomposition of muriate of ammonia by oxyd of lead may be effected in a similar manner when assisted by caloric.

*See Beckman's History of Inventions, i. 398. 400. † Lambe on the Nature of Spring Water. Johnstone on Poisons, 113.

For a description of the process, see Black's Chemistry, ii. 604.

Experiment 26. Lead and tin form an alloy, which is more fusible than either of the metals separate, in the following manner: This alloy, which is known by the name of plumbers solder, is made by fusing together in an iron ladle, two parts of lead and one of tin.

Experiment 27. That lead precipitates silver or mercury, is obvious from the following experiment. Suspend a piece of lead, scraped bright, in a concentrated solution of nitrate of silver, or nitrate of mercury. The lead, by its greater affinity for oxygen, will first become black, and then separate the silver or mercury from the solution.

A similar effect will take place by distilling muriate of mercury with granulated lead. Mercury will pass over into the receiver, and muriate of lead remain in^ the retort.

Experiment 28. That zinc precipitates lead in a metallic state forming the lead tree, is shown in the following manner: Dissolve one part of acetite of lead in 36 or 40 parts of distilled water; put this solution into a glass bottle, suspend a cylinder or ball of zinc in it, and then leave the vessel containing it undisturbed. The zinc will soon become covered with a mosslike substance, which increases gradually, shooting out symmetrical leaves of a metallic splendour, which arrange themselves into a kind of tree.

Rationale. The explanation of this experiment is obvious; the zinc has a greater affinity for oxygen than the lead has, it therefore deprives the latter of it, which being thus reduced to the metallic state, arranges itself by virtue of its molecular attraction into a symme trical form.

SECTION XV.

OF ZINC.

Experiment 1. In order to obtain zinc from its ores, they must first be torrified, and then mixt with half their weight of charcoal powder, and distilled in an earthen retort three quarters full (to which a receiver is luted) in a strong heat gradually increased for some hours. The zinc in its metallic form, is then found in the neck of the retort. In order to obtain the metal in a pure state, dissolve it in diluted sulphuric acid, and boil the concentrated solution for a few minutes upon granulated zinc. Then filter it, and precipi tate, wash the precipitate, and when dry mix it with half its weight of charcoal-powder, and submit it to a red heat in an earthen retort. Pure zinc will then be found in the neck of the retort.

Theores of zinc are analyzed in the following manner: Experiment 2. Let one part of the powdered ore be gently boiled in six of diluted nitric acid in a flask to dryness, and repeat this operation with the same ore two or three times. Then dissolve the dry mass in a sufficient quantity of water in which about one-fourth of nitric acid has been added, and precipitate the fluid by a solution of soda. Collect the precipitate on a filter, wash it by passing water over it, and re-dissolve it in muriatic acid. Then decompose this solution by liquid ammonia in excess, in order to separate the iron, lead, and alumina which may have been dissolved. If this precipitate be boiled in four times its quantity of potash, the alumina will be separated.

From the before-going solution the zinc may be separated by the addition of an acid. It may be reduced to the metallic state by strongly igniting it with half its weight of charcoal in a closed crucible.

Experiment 3. In order to analyze calamine, let it be digested repeatedly in diluted nitric acid, and the insoluble residue boiled in concentrated muriatic acid

three times, What remains after ablution with boiling water is silex.

The nitric solution obtained before contains the zinc, and also iron and alumina, if they were present in the ore. Let the solution therefore be evaporated to dryness; re-dissolve it in nitric acid, and evaporate it again as before, in order to render the iron as insoluble as possible. Then dissolve the mass in water.

A tolerably exact assay of the ore called calamine, may be made in the following manner.

Experiment 4. Mix any quantity of the pulverised ore, previously freed from sulphur by roasting, with oneeighth part of charcoal powder. Put this mixture into a crucible capable of containing thrice the quantity. Diffuse equally amongst this mixture a quantity of small grains or thin plates of copper equal to that of the calamine or ore employed, and upon the whole lay another equal quantity of grains or plates of copper, and lastly, cover this latter portion with charcoal powder. Lute a cover upon the crucible, and apply a red heat during one or two hours. The volatilized zinc will thus combine with the copper, and convert it into brass. By comparing the weight of the metal after the operation with the weight of the copper employed, the quantity of zinc united with the copper will be known.

More copper with fresh charcoal powder, may be again added in the same manner to the remaining ore, and the operation repeated with a heat somewhat more intense, in order that any zinc remaining in the ore may be thus extracted. A curious circumstance is, that a much greater heat is required to obtain zinc from its ore without the interposition of copper, than in the process now described of making brass; in which the separation of the zinc from its ore is certainly facilitated by the interposition of the copper.

Although we have no positive proof that the ancients were acquainted with zinc as a metal, yet they knew a mineral called Cadmia (from Cadmus, who first taught the Greeks to use it) which when melted with