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resembling in appearance a vegetation, and called arbor Dianæ.
Silver is not soluble in the hydro-chloric acid (muriatic acid), yet, when this acid is added to a solution of nitrate of silver, it unites to the oxide, and a white curdy precipitate falls down, which is the muriate of silver, or, in conformity with the new nomenclature, the chloride of silver. If this precipitate be fused by a gentle heat, a semi-transparent mass is formed, called formerly luna corned, or horn silver, the fused muriate of silver.
Silver is also dissolved by the sulphuric acid, and the sulphate of silver is used as a chemical test. Silver also unites to sulphur and phosphorus.
Silver, when employed for coin is alloyed with copper to increase its hardness.
Our coin contains thirty-seven parts silver and three parts copper.
This metal, called also quicksilver, is always fluid when in the usual temperature of the atmosphere ; but when exposed to an intense degree of cold, it is frozen into a solid mass, and is then malleable. The temperature necessary for this purpose is 39o. The cold is sometimes so great within the polar circle as to freeze the mercury in the thermometer; but in this country that can only be effected by exposing it to a freezing mixture.
Mercury also boils at 655°, and then evaporates, and may be distilled from one vessel to another.
It is sometimes found in nature in a pure state, but usually it is united to sulphur, with which it
forms the ore called cinnabar. The greatest quantity of it is found in Spain and South America.
When acted on by heat and air for a long time, it absorbs oxygen, and is converted into a red oxide called formerly precipitate per se: and when the heat is increased, the oxygen is given out, and the mercury re-assumes its metallic appearance. When it is agitated long in air, it is converted into the black oxide, which contains a smaller proportion of oxygen than the red oxide. It is the black oxide which is employed in mercurial ointment. Mercury is acted on by the acids, forming salts of mercury. It also unites to chlorine (oxymuriatic acid,) in two proportions, forming calomel and cor. rosive sublimate.
Mercury' when triturated with sulphur, combines readily into a black compound called ethiops mineral; when united to a larger proportion of sulphur, it forms the beautiful pigment called cinnabar.
Mercury combines with several of the metals, forming soft alloys called amalgams. The amalgam
with tin is used for mirrors: that with zinc is employed in electrical machines.
No metal is so universally diffused throughout nature as iron. It is never found in the earth in the metallic state, but is always procured from
Iron is of a bluish-grey colour. It is very ductile, for it may be drawn into wire as fine as human hair. It is also very malleable, and pos
sesses the property of being welded ; that is, of having two separate pieces united together by hammering when red hot. It is one of the most infusible of the metals, but may by intense heat be melted and run into moulds. It is in its
pure state among the hardest of the metals, but may be made to exceed all the rest in hardness when converted into steel.
It possesses the magnetic property, the load. Stone itself being an ore of iron.
Exposed to the action of the air and moisture, iron soon rusts or oxidates. It then attracts the oxygen and carbonic acid, and is changed into a reddish brown substance, which is a mixture of oxide of iron and carbonate of iron.
Iron unites to oxygen in two proportions. The protoxide of iron consists of one hundred parts of iron, and twenty-nine parts oxygen ; it is of a black colour ; hence it is called the black oxide of iron, formerly martial ethiops. It is formed when iron is heated red hot; scales form on the outside, which fly off when hammered. It is magnetic.
The peroxide is red, and consists of one hundred parts iron, and forty-three oxygen; it is called the red oxide of iron. The red oxide is formed by keeping iron filings red hot in an open vessel, and agitating them constantly till they are converted into a dark red powder, formerly called saffron of Mars.
Iron is acted on by all the acids, and various salts of iron are formed: the most remarkable are the following Sulphate of iron, formerly called copperas or
" Nitrate of iron, and acetite of iron, used in dying
Ferro-prussiate of iron, called prussian blue, used as a pigment.
Iron also combines with sulphur, phosphorus, carbon, chlorine, and iodine.
Sulphuret of iron, composed of sulphur and iron, is called also pyrites. Iron with carbon forms plumbago, commonly called black-lead, used for making pencils. Steel is another compound of iron with carbon.
The ores of iron consist either of the black oxide, which is called the magnetic iron ore, the red oxide or the red iron ore, carbonate of iron, and clay iron-stone.
The iron is separated from these ores by smelting in furnaces, where it is made to flow out into various moulds made in a kind of loam. The first
product is called cast iron. It contains some carbon and oxygen; and, it is thought, also silicium, besides casual impurities. Of this, cannon, pipes, grates, and other articles of cast iron are made. It is of two kinds : white cast-iron is very brittle ; grey cast iron is less brittle, though not malleable, but may be bored and turned in the lathe.
To render iron malleable it must be freed from those substances with which it is combined in the crude state. To effect this, it is kept in fusion in a furnace exposed to air and flame, and well stired. The oxygen combines with the carbon, and escapes in' the form of carbonic acid gas; and the earthy matter is vitrified, and rises to the surface as slag. It is then subjected to the action of large hammers and rollers, by which the remainder of the impurities is forced out. It then constitutes bar iron, also called wrought iron, fit for manufacturing.
Wrought iron is of a fibrous structure, and is the metal in a pure state. It is now extremely malle
able, soft, and easily filed, and also capable of being forged and welded. There are several varieties of iron in this state, arising from the ores from which they were procured, the process of smelting, or the intermixture of foreign substances.
One variety is called hot short iron; it is extremely ductile when cold, and on this account is employed for making wire; but when heated it is extremely brittle : it is also fusible. Cold short iron, on the contrary, is highly ductile when hot, but brittle when cold. The causes of these qualities are not precisely known, but it is said that the first is iron combined with arsenic, and that the latter contains phosphoric acid.
Iron is capable of being reduced to a third state, which is that of steel. It is converted into steel, by exposing it to heat in contact with carbonaceous substances, which unite themselves with it. Steel is, therefore, iron united to carbon, and is made by three processes.
Natural steel is made by keeping cast iron in a state of fusion in a furnace, its surface being all the while covered deep with scoriæ; part of the carbonic acid gas escapes, while another part combines with the iron. This steel is inferior to the other kinds.
Steel of cementation is made by placing bars of iron in charcoal powder, and exposing them to a strong heat in a furnace for six or eight days. The iron and the carbon thus combined constitute what is here called blistered steel. When this is rendered more malleable by the operation of the hammer, it is called sheer steel.
Cast steel is made by fusing blistered steel with pounded glass and charcoal powder, in a close crucible. It is also made merely by fusing iron with