178

SILVER.

LESSON 79.

Silver and Mercury.

Ful'minate, to explode with a loud report.

SILVER is a heavy, sonorous, brilliant, white metal, only moderately hard, but exceedingly ductile, and of great malleability and tenacity. It is found in various parts of the world, particularly in Peru and Mexico, in a metallic state; also in the state of an alloy, of a sulphuret, of a salt, and in that of an oxyd. It is the most brilliant of metals, and nothing surpasses it in splendour except highly polished steel. It is chiefly used for ornamental work, for domestic utensils, and for current coin: but for these purposes it is generally alloyed with copper, without which it would not have sufficient hardness to sustain much wear. You may know when silver is pure by heating it in a common fire, or in the flame of a candle; if it be alloyed, it will become tarnished; but if it be pure silver, it will remain perfectly white. Of the salts of silver the nitrate is best known, and when melted and run in moulds, it forms the lunar caustic of the apothecary. A solution of it mixed with a little gum water, forms, in conjunction with an alkali, the indelible ink, used in marking linen.

Silvering may be performed on the same substances, and by similar methods with gilding. But as works of this kind are liable to tarnish, they are seldom used. Plating with silver is performed in the following manner: one of the surfaces of an ingot of copper is rendered smooth and clean, and is sprinkled over with a saturated solution of borax; upon this is laid a plate of fine silver, about one twelfth the weight of the copper, and the two are carefully bound together by wire. The mass is now exposed to a full red heat, and the silver adheres to the copper. The ingot is then passed through a rolling-press, and formed into a plate; both the silver and copper extending uniformly during the whole process, at the conclusion of which, the two metals are inseparably united.

Mercury or quicksilver has been known from the earliest ages of the world. In the temperature of our atmosphere, it is a white fluid metal, having the appearance and brilliancy

of melted silver. When submitted to a sufficient degree of cold, it is similar in appearance to other metals, and may be beaten into plates. At the poles it would probably be always solid. It readily combines with several of the other metals, and forms with them what are called amalgams. Mercury is used in large quantities for separating gold and silver from their ores; for silvering mirrors, for water-gilding, for making barometers and thermometers; by the philosophical chemist for many purposes of the laboratory; and in the manufactory of vermilion. It has also various and important uses in medicine. By dissolving mercury in nitric acid, a fulminating powder is obtained, two or three grains of which, laid on an anvil and struck smartly with a hammer, will explode with a loud report. Four grains will occasion indentation in the hammer and anvil. By exposing mercury to cold of a proper degree of intensity, which may be easily accomplished by certain freezing mixtures, it becomes a solid metal. If a lump of this be dropped into a cup of warm water, the solid metal will immediately become fluid, and the fluid water in the same instant will become solid. If a glass be used for the experiment, it should be infolded within a cloth to prevent accidents; for sometimes it will be shivered in pieces by the rapidity of the action.

The quicksilver mine of Guanca Velica, in Peru, is 170 fathoms in circumference, and 480 deep. In this profound abyss are seen streets, squares, and a chapel. Thousands of flambeaux are continually burning to enlighten it. The mine generally affects those who work in it with convulsions. Notwithstanding this, the unfortunate victims of an insatiable avarice are crowded together, and plunged naked into these abysses. Tyranny has invented this refinement in cruelty, to render it impossible for any thing to escape its restless vigilance :—

For in the dark Peruvian mine confined,
Lost to the cheerful commerce of mankind,
The groaning captive wastes his life away,
For ever exiled from the realms of day;
While all forlorn and sad, he pines in vain

For scenes he never shall possess again. FALCONER. QUESTIONS.-1. What is silver? 2. In what states is it found? 3. For what used? 4. How can you ascertain its purity? 5. What is said of nitrate of silver? 6. Of silvering? 7. Plating? 8. Describe

mercury. 9. For what is it used? 10. What is said of fulminating powder? 11. Of mercury as a solid metal? 12. What is the description of the quicksilver mines in Peru? 13. How much must the temperature of mercury be reduced before it will become solid? (see Appendix.) 14. What is said of freezing mixtures?

LESSON 80.

Copper and Lead.

Concen'trated, usually applied to fluids which are rendered stronger by evaporating, by means of heat, a portion of the water they contain.

Heterogeneous, dissimilar in nature. Homogeneous, having the same nature or principles.

Culinary, relating to the kitchen.

COPPER is a brilliant metal, of a red colour, very hard, sonorous, and elastic; and the most ductile of all the metals, except gold. Its malleability is also so great, that it is hammered into leaves, and sold in thin paper books in imitation of leaf-gold. It will not burn so easily as iron; which is evident from its not striking fire by collision. On this and other accounts it has been substituted for iron in the machinery which is employed in gun-powder mills. The salts of copper are numerous, and much used in the arts connected with chemistry. Concentrated sulphuric acid dissolves copper by the aid of heat, and thus the sulphate of copper or blue vitriol is formed. Copper exposed to the vapour of vinegar or acetic acid becomes acetate of copper or verdigris. All the salts of copper are poisonous, therefore great care should be taken not to taste wantonly the solutions. The uses of this metal are too various to be enumerated. Besides its employment to make boilers and other vessels of capacity, and to sheathe the bottoms of ships, it enters as a component part into several of the most valuable alloys. The most important of these alloys is brass, which is formed by the union of copper and zinc, though brass is never made with pure zinc, but generally with calamine, which is a native oxyd, or rather carbonate of zinc. Bronze and gun-metal are formed by the union of copper and tin in the proportions of a hundred parts of the former to ten or twelve of the latter. Bell-metal is also an alloy of tin with copper, but this usually contains one fourth

of its weight of tin. Oxyd of copper is used by the colouredglass makers. It forms a beautiful green glass.

Lead is a metal of a bluish white colour, very brilliant when first cut with a knife, but it soon tarnishes by exposure to the air; it will mark writing-paper, though in a fainter manner than plumbago. It is malleable and ductile, but possesses very little tenacity. Lead may be mixed with gold and silver in a moderate heat, but when the heat is much increased, the lead rises to the surface, combined with all heterogeneous matters. Upon this property of lead is built the art of refining the precious metals. If melted lead be exposed to the atmosphere, a greyish-yellow powder begins to form upon the surface. By keeping it exposed for some time the powder becomes more yellow. In this state it is called massicot, or yellow oxyd of lead. By a second exposure this oxyd appears capable of combining with more oxygen. It gradually changes colour, and ultimately assumes a splendid red. In this state it is called minium or red lead. The process requires considerable management with regard to heat and the access of air. If the heat be too great or rapid, the lead becomes converted into a flaky substance, called litharge; and a still greater heat converts it into a clear, transparent yellow glass. Thin plates of lead, exposed to the fumes of vinegar at a certain temperature, are gradually corroded and converted into a heavy white powder, used as paint, and called white lead.

The ore of lead is so poisonous, that the steam arising from the furnaces where it is worked, infects the grass in all the neighbouring places, and kills the animals which feed on it. Culinary vessels, lined with a mixture of tin and lead, which is the usual tinning, are apt to communicate to acid foods pernicious qualities, and require to be used with great caution. The same may be said of liquors and other acid substances kept in glazed ware, and of wines adulterated with litharge, and such other preparations of lead as are sometimes used for the purpose of rendering them sweet.

QUESTIONS. 1. What is copper? 2. Why is it substituted for iron in some machinery? 3. What is said of the salts of copper? 4. What is brass? 5. What are bronze and gun-metal? 6. Bell-metal? 7. Describe lead? 8. Why is it used in refining metals? 9. How does lead become oxydized so as to form massicot, and minium? 10. What is litharge? 11. How is white lead formed? 12. What is said of the poisonous qualities of lead?

It

LESSON 81,

Iron and Tin.

Chalyb'eato, a term descriptive of those mineral waters which are impregnated with iron.

Pyrites, a name given to certain ores, as of iron, copper, tin, &c. which contain a large quantity of sulphur, and have a metallic lustre.

IF utility were made the standard of estimation, iron would hold the first place in the class of metals, and would be counted more valuable than gold, as it appears indispensably necessary to the carrying on of every manufacture. It appears to be one of the principal means of civilizing mankind. There has never been an instance of a nation, acquainted with the art of manufacturing iron, which did not in time attain to a degree of civilization infinitely beyond the inhabitants of those countries where this metal was wanting, or its use unknown. It is plentifully and universally diffused throughout nature, pervading almost every thing, and is the chief cause of colour in earths and stones. may be detected in plants and in animal fluids. There is a great variety of iron ores, which have different names given them by the workmen, and are of very different qualities. They are chiefly composed of the oxyds of iron and clay. This metal is susceptible of two degrees of oxydizement—the scales, which are detached from forged iron by a high degree of heat, are in the state of black oxyd, and the common rust of iron is the red oxyd. If a bar of iron be heated red-hot, and a stick of sulphur applied to it, a fluid substance will drop from its end, which is found to be a compound of sulphur and iron, and in chemistry is called sulphuret of iron. Iron-filings mixed with sulphur, and made into a paste with water, in a certain time become very hot, and even produce flame. This mixture is sometimes buried under the ground to produce an artificial volcano. In this experiment the water is decomposed, the oxygen unites with the iron to form an oxyd of iron, and with the sulphur to form sulphuric acid, while the hydrogen combines with another portion of the sulphur, and produces sulphuretted hydrogen gas, which occasions the flame. Green vitriol or copperas, which is of so much use in dyeing, in colouring