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SUBDIVISION IV. CADMIUM, COPPER, SILVER, MERCURY, LEAD, BISMUTH,

PALLADIUM, TIN, ANTIMONY, ARSENIC, PLATINUM, RHODIUM, RUTHENIUM, IRIDIUM, OSMIUM, GOLD, TUNGSTEN, MOLYBDENUM, VANADIUM.

The prevailing colour of these metals is white, one, however, copper (Cu) is red, and one, gold (Au), is yellow. Their specific gravity varies from 5.75 to 21:47. The greater number of them are very easily obtained from the compounds (ores) in which they exist in nature, and as these ores are tolerably abundant, they exert an important influence upon civilization. Those found in the largest quantity and obtained with the greatest ease are lead, copper, tin, silver, mercury, gold, bismuth, antimony, and arsenic; platinum and palladium are of rarer occurrence, and the remainder are very seldom met with. As a rule they do not, when exposed to the air, combine with its oxygen, or at the most become covered with but a slight film of oxide or tarnish ; so comparatively slight indeed is their affinity for oxygen, that the oxides of many of them are decomposed by heat alone into metal and oxygen. As a class also they exert no action upon water or hydrochloric acid. These metals are not magnetic.

I. CADMIUM=Cd. The metal cadmium does not decompose water at the ordinary temperature, and only slightly tarnishes upon exposure to air; it is nevertheless a very oxidizable metal at a higher temperature, and when heated in the air burns with the formation of an oxide (Cd, O) of a brown or brownish-yellow colour. Hydrochloric acid acts upon it but slowly.

The colour of cadmium is white with a tinge of blue; it is soft and flexible, crackling like tin when bent; it is very fusible, melting below a red heat; it volatilizes somewhat below the boilingpoint of mercury (360° C.), and its vapour has no odour. The density of the metal is 8.604 after fusion, and 8.694 after hammering.

II. COPPER=Cu. The metal copper does not decompose water at the ordinary temperature, and but very slowly when raised to a high degree of heat. On exposure to moist air it tarnishes, and when heated in the air it absorbs oxygen and yields two oxides (Cu,O and Cu, 0); these, however, do not yield up their oxygen when further heated. Hydrochloric acid acts upon this metal with great difficulty.

Copper has a well known red colour; it is malleable; at about 788° C. it melts, and volatilizes sensibly at a very elevated temperature. Its density after fusion is 8.85, and after hammering 8.95.

III. SILVER=Ag. The metal silver does not decompose water, or withdraw oxygen from dry or moist air; if, however, it is heated in contact with air, at an elevated temperature it absorbs, or more properly, dissolves oxygen, but yields it up again on a further increase of heat. It is acted upon by hydrochloric acid with the greatest difficulty.

The peculiar lustre of silver is perhaps more beautiful than that of any other metal. It is very malleable. At about 1000° C. it melts, and volatilizes slowly at a very high degree of temperature. Its density is 10:47 after fusion, and 10:51 after hammering.

IV. MERCURY=Hg. The metal mercury does not decompose water at any temperature, nor does it combine with oxygen when exposed to dry or moist air; if heated in the air it combines with oxygen, forming the oxide (Hg,0), which is again resolved into its constituents at a higher degree of heat. Hydrochloric acid is not decomposed by this metal.

The great peculiarity of mercury is its liquidity at common temperatures; at -40° C., however, it becomes solid, and at 360°C. it boils, and is converted into a colourless vapour. In lustre and colour it resembles silver, yet has a tinge of the blue-grey hue of lead. Its density is 13.59 at 4° C.

V. LEAD=Pb. The metal lead does not decompose perfectly pure water; it tarnishes slightly in moist air ; if heated in the air it rapidly absorbs oxygen, and the oxide thus formed (Pb, 0) is not decomposed by heat alone into metal and oxygen. Hydrochloric acid acts upon this metal with great difficulty.

Lead is a metal of a bluish-white lustre, very malleable, melting at 334°C., and volatilizing to a considerable extent at high temperatures. Its density is 11.445, and increases slightly by hammering.

VI. BISMUTH=Bi. The metal bismuth appears not to decom

pose water if the latter is quite free from air; it tarnishes slightly in damp air; and if heated in the air is converted into its oxide (Bi,O), which is not decomposed by heat. Hydrochloric acid acts upon it very slowly.

Bismuth is of a reddish-white colour, rather brittle; it melts at 247° C., and can be distilled at a very high temperature. Its density is 9.82, and is slightly diminished by compression.

VII. PALLADIUM=Pd. The metal palladium does not decompose water; it does not tarnish in the air unless heated, when a blue film of oxide appears on the surface which vanishes upon further heating : cold hydrochloric acid does not attack it.

Palladium is a metal of a greyish-white colour; it does not melt at the temperature of the blast-furnace. Its density is 11:3 after fusion, and 11.8 after hammering.

VIII. TIN=Sn. The metal tin does not decompose water, nor does it absorb oxygen from the air; heated in the air it forms an oxide which an accession of temperature does not decompose ; it is but slowly attacked by hydrochloric acid in the cold.

Its brilliant white colour is well known; it is malleable, and melts at a temperature of 228° C. Its density is 7.291 after fusion, and 7.299 after rolling. .

IX. ANTIMONY=Sb. The metal antimony does not decompose water or attract oxygen from the air at ordinary temperatures ; heated in the air it oxidizes, and the oxide produced is not decomposed at an increased heat: cold hydrochloric acid acts upon it with extreme slowness.

It has a bluish-white colour, is very brittle, melts at 430° C., and has a density of 6.71.

X. ARSENIC=As. The so-called metal arsenic does not decompose water freed from air, nor does it absorb oxygen from dry air. It becomes oxidized by exposure to air and water, or to moist air only. When heated in the air it burns into an oxide not easily decomposable by heat. Hydrochloric acid is readily decomposed by this body.

The metal has a steel-grey colour, is very brittle, and volatilizes without melting at 300° C. Its density is 5.75,

XI. PLATINUM=Pt. The metal platinum does not decompose water except at a most elevated temperature; it does not absorb oxygen from the air at any temperature, nor does hydrochloric acid exert any action upon it.

Its colour is white with a tinge of grey. It is malleable, and possesses the property of welding at a white heat. It melts only at the temperature of the oxyhydrogen blowpipe. Its density is 21:16 after fusion, and 21:45 after hammering.

XII. The metals rhodium, iridium, ruthenium, and osmium are very rare, and are not likely to come in the way of the student. XIII. GOLD=Au. The metal gold does not decompose water, nor does it tarnish in the air or absorb oxygen from it at any temperature: it is wholly unattacked by hydrochloric acid.

Its rich yellow colour is well known. It melts at about 1200° C.; its ductility is very considerable. Its density is 19.2 after fusion, and 19:3 or 1904 after hammering.

XIV. The metals tungsten, molybdenum, and vanadium are not likely to pass through the hands of the student.

Metals, the majority of which do not expel Hydrogen from Hydro

chloric Acid, even at the boiling temperature.

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SUBDIVISION V.

HYDROGEN. The only member of this subdivision is the gas hydrogen, which, from the numerous chemical analogies which it bears to the metals, is expected, if ever condensed, to appear in the metallic form ; its gaseous state at ordinary temperatures is no argument against this view, since it must be remembered that many of the metals, as mercury, zinc and sodium, are known as transparent gases at an elevated temperature; it has not yet, however, been condensed, and so the features which its liquid or solid forms may present are merely a matter of conjecture.

Hydrogen is an exceedingly abundant element, occurring in combination with oxygen as water; its affinity for this body and for chlorine is very great, as exemplified by the facts stated above, which show that only a few of the metals have, by reason of their superior affinity, the power of directly expelling hydrogen from these combinations.

Since hydrogen is a substance frequently employed in chemical operations, and as it differs in many material points from the elements of the same class which have been described, it is important that the student should prepare it and examine its properties.

It occurs in nature, as many of the metals do, combined with oxygen, and in this form of combination (H, O) it constitutes a large part of terrestrial matter; it also occurs in commerce combined with various other elementary and compound bodies, forming a large class of substances to which the name of acids has been assigned, such as hydrochloric (HCI), sulphuric (H, 80,), and nitric acid (H NO.); from any one of these compounds hydrogen may be set free by employing a suitable process, or in other words, by presenting to the hydrogen compound some substance which has a greater tendency to combine with that body with which the hydrogen is united than the hydrogen itself possesses. Thus, if potassium be added to water, hydrogen (H) and the substance called potash, or hydrate of potassium (K HO), are ob

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