These metals are unable to decompose water at any temperature. They have but a feeble attraction for oxygen; the oxides of the first five being decomposed below a red heat, the metal remaining in an uncombined form; and in many cases simple exposure to a strong light produces a similar decomposition: all of them yield more than one series of salts. Mercury and silver are often found mineralized in the form of sulphides, but the other metals of this group usually occur in the native state, several of them being frequently associated together. Their attraction for sulphur and for chlorine is much stronger than for oxygen. All of them form at least two chlorides, and some three or even four: the chlorides of the noble metals have a strong tendency to form double chlorides with the chlorides of the metals of the alkalies. Silver exhibits considerable analogy with lead: it is powerfully basylous; palladium is somewhat allied to copper. § II. GENERAL PROPERTIES OF THE COMPOUNDS OF THE METALS WITH THE NON-METALLIC ELEMENTS. (533) THE OXIDES.-The most important compounds of the metals with the non-metallic bodies are those which they form with oxygen. The oxides in many cases constitute abundant and valuable metallic ores; such as the different forms of hæmatite, the specular and magnetic iron ores, and tinstone, the ordinary ore of tin. The metallic oxides may be subdivided according to their chemical function into 3 classes :-viz., 1, basic oxides; 2, saline or indifferent oxides; and 3, metallic anhydrides, which when hydrated form the metallic acids. The atomic proportions in which the constituents of the principal varieties of metallic oxides are united are exhibited in the following table : 2 1. Suboxides, „Ne, of the type H2O; feebly basic, such as— Suboxide of copper „Eu¿Ð. 2. Monoxides,* M', or N", of the type H.; strongly basic, such as- Oxide of silver Ag Lime Єa". * These oxides may, in fact, be regarded as compounds formed upon the type 2 THE OXIDES. 6 343 3. Sesquioxides, N'""',, of the type H., ; feebly basic, neutral, or even acid, such as 4. Three-fourths oxides, N,,, of the type H.; saline oxides, such as 2 3 Magnetic oxide of iron, Fe" (Fe"), or Fe ́ ́ЂFe ́ ́¿Ð ̧ 2 5. Binoxides, Nive, of the type HO; rarely basic, but generally neutral or acid, such as— Binoxide of platinum, Pt1Ð ̧ Binoxide of barium, BaÐ, 6. Teroxides, Nie, of the type, H.; metallic anhydrides, such as 3 Molybdic anhydride, Movie, 7. Anhydrides, R',,, of the type H100 Arsenic anhydride, As,, Antimonic anhydride, Sb... The oxides constitute so important a series of compounds, that it will be necessary to consider their relations, particularly to water and to the acids, somewhat more in detail, classifying them in the order just indicated. of a single atom of water, HH, if each atom of hydrogen in the molecule is displaced by an atom of a metallic monad, such as potassium; or if both atoms of hydrogen be displaced by a single atom of a metallic dyad, such as barium, we have an analogous oxide; for example: : HHO, water, Ba", anhydrous baryta; but if only one atom of hydrogen be displaced by the metallic monad we have a hydrate of the metallic oxide. If the metallic dyad displaces half the hydrogen of two atoms of water, we have a hydrate of the oxide of the metallic dyad, as for instance : In the sesquioxides and teroxides the molecular type is a group consisting of three atoms of water, each atom of the metal representing 3 or 6 atoms of hydrogen in the combination; alumina being (Al""),,, and its normal hydrate (A"")Н ̧Ð ̧. The binoxides correspond in composition to a group containing 2 atoms of water; the oxides to a group containing 4 atoms of water, and so on, as indicated in the table. 344 VARIETIES OF THE METALLIC OXIDES. 1. Suboxides, of the type,,N,.-A few of the dyad metals, such as copper, lead, and mercury, form oxides in which one atom of the metal, which usually is equivalent to two atoms of hydrogen, becomes for the time equivalent only to a single atom of hydrogen. Thus we have the cupreous oxide, or red oxide of copper (Eu¿Ð); mercurous oxide, or black oxide of mercury (Hg,O); and a suboxide of lead (Pb,). Though each of these oxides gives rise to an unstable series of salts, it frequently becomes decomposed into the normal oxide and free metal; suboxide of copper, for instance, becoming converted into metallic copper and the red oxide; Єu, Єu+Єue; but with hydrochloric acid the reaction is as follows; Eu,+2 HCl=H2O+ 2 EuCl. No normal hydrates of these oxides appear to exist, the suboxides of mercury and lead being anhydrous, and the yellow hydrate of cupreous oxide being 4 Єu,,H,, instead of EuHO. 2. Monoxides, of the type M',, or N"O.-This class of oxides includes all the most powerful bases: they are formed by the union either of 2 atoms of a metallic monad with 1 atom of oxygen, or by the union of 1 atom of a metallic dyad and 1 of oxygen. The first subdivision includes the five alkalies and the oxides of thallium and silver. Among the members of the second subdivision are included the alkaline earths, the oxides of lanthanum, didymium, magnesium, zinc, and cadmium, and the protoxides of cerium, uranium, cobalt, nickel, iron, chromium, manganese, tin, copper, lead, mercury, and palladium. The anhydrous oxides of the alkali-metals become converted into hydrates with extrication of intense heat on the addition of water, which dissolves them rapidly and in large quantity; one atom of water and one of alkali yielding two atoms of the hydrate: e.g., KKO+HHO= 2 KHO. The hydrates of the alkalies cannot be again decomposed by exposure to heat, but are slowly volatilized without decomposition by a prolonged elevation of temperature. No definite hydrate of oxide of silver is as yet known, though it is soluble in a very slight degree. 2 The action of water upon anhydrous baryta, strontia, and lime is also very energetic, a single atom of the hydrate being in each case formed by the combination of single atoms of water and the earth; as, for instance, Єa+H2O=Єaн ̧ ̧. The hydrate of lime requires a full red heat for its decomposition, but the hydrates of baryta and strontia fuse at an elevated temperature, and do not part with their water even by prolonged ignition. These hydrates are soluble in water, though that of lime is but sparingly so. Magnesia combines very slowly with water. It is VARIETIES OF THE METALLIC OXIDES. 345 very sparingly soluble; the oxides of lead and mercury are somewhat more soluble. The other oxides above enumerated do not when anhydrous combine with water when mixed with it. Their monohydrates may usually be obtained by precipitating a solution of one of their salts by the addition of a solution of one of the alkalies in slight excess. The hydrated oxide of copper has the formula Єue, 2 H2; those of lead and tin consist of 2 Pb,H¿Ð, and 2SnᎾ,H Ꮎ, Most of the monoxides, by their reaction with the ordinary acids, form salts which are neutral in their action upon test-paper. The following equations may be taken as exemplifying some ordinary cases of the action of acids upon these oxides and their hydrates: 3 3. Sesquioxides, of the type N'"',.-Most of the oxides of this class are feeble bases; among them are included alumina, and the sesquioxides of cerium, uranium, iron, manganese, chromium, antimony, and bismuth. They furnish salts when acted upon by acids, but all these salts redden litmus: usually 3 atoms of water are separated by the reaction of the base upon the acid; as, for instance, The oxides of iron, antimony, and aluminum, occasionally, and the oxide of uranium invariably, however, form salts, with the elimination of 1 atom of water only, two-thirds of the oxygen remaining in a state apparently of intimate combination with the metal; for instance: Sesquioxides of cobalt and nickel exhibit no tendency to form salts by reaction either with acids or bases. When heated with hydrochloric acid, they evolve chlorine and furnish a lower chloride; no chloride corresponding to these sesquioxides is known : 2 2 : €02Ð ̧+6 HCl=2 €0Cl2+ Cl2+3 H2O. Sesquioxide of arsenic possesses no basic properties, but when dissolved in water is feebly but decidedly acid; the sesquioxide of gold is insoluble in water, but its hydrate (H,,Au, ̧, or Auн→2) presents the properties of an acid, though they are but feebly marked. 346 VARIETIES OF THE METALLIC OXIDES. The basic sesquioxides have but a feeble attraction for water; when precipitated by alkaline solutions from the solutions of their salts, they furnish very bulky gelatinous precipitates, which easily lose water during drying. 4. Three-fourths Oxides, of the type N2, or N"→‚N”''203· These oxides do not form salts with acids, being probably compounds of a protoxide with a sesquioxide, into the compounds corresponding to which they are resolved by the action of acids; as for instance: Fe3O4+8HCl= FeCl2+Fe2Cl + 4H,. Magnetic oxide of iron, Fe,, or Fee,Fe,,, is the best representative of the class, which is rather numerous, and includes corresponding oxides of chromium, uranium, manganese, nickel, and cobalt, besides the double oxides, chrome ironstone, Fee,Cr,,; spinelle, MgOA,,; gahnite, ZnO,Ale 4 2 5. Binoxides of the type M,O, or Nive. Of these there are three distinct varieties. The first variety comprises the basic oxides, of which the binoxides of platinum (Pt,) and palladium are the most important: they are feeble bases, and with water form hydrates, such as (Pt,, 2 H2O). The second variety is represented by the peroxides of sodium (Na,,) and silver (Ag,,), and those of barium (Ba✪2), manganese, and lead. These oxides do not form corresponding salts with acids, nor do they yield corresponding chlorides: they retain the second atom of oxygen but feebly. When heated with oil of vitriol they give off oxygen, and form a sulphate corresponding to the protoxide; 2 MnO2+2 H2SO ̧=2 MnSÐ ̧+→2+2H ̧Ð. When treated with hydrochloric acid they either furnish peroxide of hydrogen or liberate chlorine and form water; for example: 4 Of these oxides some, as those of potassium and sodium, are decomposed with evolution of oxygen when thrown into water; peroxide of barium forms the hydrate (BaÐ,, 6 H2O); whilst the peroxides of manganese, lead, and silver do not become hydrated, the three oxides last mentioned conduct the voltaic current: peroxide of lead, indeed, exhibits some properties of a metallic anhydride, and when fused with the hydrated alkalies furnishes compounds known as plumbates, whilst water is evolved; 2 KHO+ PbO2=K,Pb✪2+H2Ð. 3 In the third variety of binoxides the character of the metallic anhydrides is distinctly marked; such, for example, as the stannic |