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compositions of the gaseous molecules of these compounds are
expressed by the formulae As.. and Sb,06 The formulae
of the following oxides of nitrogen are molecular N,O, NO,
NO, N,0. A few oxychlorides, e.g. NbOCI,, have also been
gasified.

The formulae of the other compounds are not necessarily
molecular ; they are the simplest formulae that can be given,
consistently with the determined values of the atomic weights

of the elements, and with the reactions of the compounds. 427 The hydrides MH, are gases under ordinary conditions.

Ammonia, NH,, is obtained in small quantities by the direct union of nitrogen and hydrogen under the influence of the induced electric discharge; also in many reactions in which hydrogen is produced in contact with nitrogen, e.g. when steam and nitrogen are passed over hot iron, or when nitrogen is produced in contact with hydrogen, e.g. when hydrogen and nitric oxide are passed over hot finely divided platinum. Ammonia is usually prepared by heating a mixture of ammonium chloride and lime;

2NH,Cl + CaO = CaCl, + H,0 + 2NH,.
Phosphoretted hydrogen or phosphine, PH,, may be obtained
by heating a mixture of phosphonium iodide and an alkali;
PH I + KOHAq = KIAq+H,0 + PH,; it is however more
usually prepared by heating a solution of an alkali with
phosphorus; 3KOHAq + 31,0 + 4P = 3KH PO Aq + PH,

3H
(potassium hypophosphite remains in solution, phosphine is
evolved as a gas).

Arsenuretted hydrogen or arsine, AsH,, is obtained by
producing hydrogen in contact with a solution of an arsenic
compound. Antimonuretted hydrogen, or stibine, SbH,, is
obtained by a similar method. Thus,
M.O,Aq+xM,O,Aq+12H +«H=2MH +3H,0+«H+«MO Aq
(the hydrogen must be produced in contact with the M,O,Aq; M=As or Sb).

Ammonia, NH,, combines with most acids to form am-
monium salts ; e.g. NH2 + HCl = NH,Cl; 2NH2 + H SO,
(NH),SOC. Phosphine, PH,, combines with hydriodic acid,
and with hydrochloric acid under increased pressure, to form
phosphonium salts; e.g. PH, + HI = PHI. (Regarding ammo-
nium salts s. Chap. XI. pars. 210, 211, and Chap. XVII.
par. 371.) Arsine and stibine do not combine with acids.

The hydrides MH, can be oxidised to oxides and water;
ammonia is oxidised by mixing it with much oxygen and

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bringing a flame to the mixture; water, nitrogen, and a little ammonium nitrate (NH NO,) are formed; phosphine is oxidised to phosphorus pentoxide (P,03) and water by mixing it with air or oxygen and raising the temperature; arsine and stibine are oxidised by mixing with air or oxygen

and bringing a flame to the mixture; if much oxygen is present the products are water and arsenious or antimonious oxide; if little oxygen is present, water, arsenic or antimony, and a little arsenious or antimonious oxide, are formed.

Arsine and stibine are decomposed by heat; ammonia and phosphine are much more stable towards heat.

The most important and best studied oxides of the 428 elements of Group V. are those whose composition is expressed by the formulae M,O, and M,0g, respectively.

The trioxides M,0, may be formed by the direct union of their elements; N5,0, and Ta, O, have not yet been prepared, and as erbium has not been isolated it is uncertain whether the oxide Er,0, would or would not be formed by heating erbium in oxygen. Nitrogen and oxygen combine only when a mixture of the gases is submitted to the continued action of electric sparks, and then only a small quantity of N,Og is formed; the other elements of the group are readily oxidised to M,0, by heating in air or oxygen.

The oxides M,0, may be divided into three classes: (1) acidic oxides, N, O, P Os; (2) basic oxides, Di, 0.3, Er 03, Bi,Oz's (3) oxides which are both acidic and basic, As Oy, Sb 0 (? V,03). The oxides N o, and P,O, dissolve in water to form solutions of nitrous acid ÄNO, and phosphorous acid H PO,

, respectively; neither oxide shews the smallest tendency to interact with acids and form salts. The oxides Di,O,, Er, 0 and Bi 0, interact with acids to produce salts; they are all insoluble in, and unchanged by contact with, water. Arsenious oxide, As, 3, dissolves in water and the solution interacts with caustic soda or potash to form salts of the composition M Aso, (M = Na or K); but no oxyacid derived from As, has been obtained. Antimonious oxide, Sb,Оg, is slightly soluble in water and the solution reacts with potash or soda to form antimonites M SbOg; the acid H Sb0, is known as a solid, but it is not obtained by the direct interaction of water with Sb Oz. Arsenious oxide interacts with concentrated hydrochloric acid to form arsenious chloride, AsCl,; it is also said to form a salt AsKC,H,O, by reacting with solution of potassiumhydrogen tartrate, antimonious oxide forms SbCl, by reacting M. E. c.

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with concentrated hydrochloric acid, it forms SbKC,H,O, by dissolving in KHC 11,0 Aq and crystallising, and it probably interacts with concentrated sulphuric acid to form Sb (SO) Vanadium trioxide VO, is said to interact with acids to produce a series of unstaốle, easily oxidised, salts.

The pentoxides, M,Og, can be obtained by heating the elements in oxygen when M=P, V, Nb, or Ta; by evolving oxygen in contact with M,Owhen M = As, Sb, Di, or Bi; and by withdrawing water from nitric acid in the case of N,0; (2HNO3-H,=N,Os).

The oxides NO, and P,0; dissolve in water to form acid solutions from which the acids HNO, (from N 03), HPO, H PO, and H PO, (from P,0) can be obtained. The oxides As o, and Sbo. are slightly soluble in water forming acid solutions from which salts can be obtained, e.g. Ag, AsO,, KSbO3; V,0, is scarcely soluble, Nb,05, Ta,,, Di, 0 , and Bi, o, are insoluble, in water; salts of the forms MVO, MTao,, and M,Nb,, &c. are obtained by heating the pentoxides of Ý, Ta, and Nb, with molten potash or soda; no salts derived from Di,o, or Bi,O, are known; Bi,O, however dissolves in much molten potash and possibly forms very easily decomposed salts.

Of the remaining oxides, nitrous oxide N, O, nitric oxide NO, nitrogen dioxide NO,, and nitrogen tetroxide N, O,, are gases; they are all obtainable by reactions between aqueous solutions of nitric acid and various reducing agents; the oxide NO, exists at moderately high temperatures, when this oxide is cooled it becomes very dark reddish black in colour and the vapour density now shews that its molecular composition is expressed by the formula NO. All the oxides of nitrogen are acidic; none shews any basic properties.

The haloid compounds are generally obtained by the direct union of their elements; also in many cases by dissolving the trioxides, M,0, in haloid acid and evaporating. Those elements of the group which form pentachlorides MCI, are P, Nb, Sb, and Ta; the compounds MCl, are produced by heating these elements in excess of chlorine. Trichlorides MCly, are formed by heating arsenic or bismuth in chlorine ; vanadium heated in a stream of chlorine forms the tetrachloride VCI. Pentahaloid compounds (MX,) of nitrogen, vanadium, arsenic, didymium, and bismuth, have not yet been obtained; no trihaloid compound (MX,) of tantalum is known; haloid compounds of erbium have not as yet been isolated. Vanadium

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is the only member of the group which forms a haloid compound of the form MX, stable in the state of gas. Niobium and tantalum pentachlorides can be gasified; the pentachlorides of phosphorus and antimony are dissociated to MCI, + Cl, when heated.

The haloid compounds are all decomposed by water, generally forming solutions of haloid acid and the hydrated oxide of the element; thus PCI, gives H PO,Aq, Asci, gives As O, Aq, VCI, gives V,0 Aq, NbCl, gives N6,02H,O, Tači, gives Tao, XH,O, Sből, gives S6,0, Aqif much warm water is used but solid SbỚCl if less water is added, in each case HCIAq is also formed ; BiCl, gives BioCl and HCIAq whatever be the quantity, or the temperature, of the water employed.

Many oxyhaloid compounds of Group V. exist; the more important belong to the forms MOCI and MOCI,

The sulphides, M.S,, of the lower members of the group 430 generally interact with alkaline sulphides to form thio- (or sulpho-) salts; thus As, S, dissolves in ammonium sulphide solution to form a solution of ammonium thio-arsenite, (NH),AsS,; Sb S, under similar conditions forms a solution of NH Sb. The best studied and apparently most distinctly acidic sulphides are As Sy and Sb,Sg; P,S, and V S, also interact with alkaline sulphides to form thiosalts. Ta S, is not known, but Ta,S4 is said not to react with alkaline sulphides. Bi S, shews no acidic properties. Nitrogen forms the sulphide NS,; it is prepared by passing ammonia into sulphur dichloride (SCI); it is very easily decomposed by heat. Phosphorus forms several sulphides, P,S, PS, P, S, P,S, &c.; they are generally obtained by direct union of phosphorus and sulphur. The highest sulphide of vanadium V S, is formed by passing sulphuretted hydrogen over hot V,05; Ta S, is produced by passing carbon disulphide (CS.) over hot Ta O. The sulphides As,Sa, Sb,Sz, and Bi,S, are produced as solid precipitates when sulphuretted hydrogen is passed into acidulated solutions of the oxides M,Oz.

The acids formed by the combination of elements of 431 Group V. with hydrogen and oxygen are numerous and important. The following table shews the compositions of

. the best marked of these acids, and exhibits the relations of composition between them and their corresponding oxides.

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HNO3

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Acid.
Corresponding

Remarks.
Oxide.
HNOA*

N20 Acid not formed from oxide; but

aqueous solution of acid boiled

gives the oxide. HNO.AZ

N203 Oxide dissolves in water to form a

solution of the acid. N,Og Oxide reacts with water to form the

acid; oxide also obtained from the acid by withdrawing water,

but not by action of heat. H.H.PO,A

No oxide known corresponding to

acid. HQ.HPO,Aq P,0zl Oxides interact with water to form HPO3, H,PO. H.P,0,

P205)

the acids; oxides not obtained

by heating the acids. HVO3, H.V,O(also salts 1,05 Acids not obtained directly from of form M,VO)

oxide; oxide obtained by heating

the acids. Salts of form MASO, and As,, Solution of oxide in water interacts M.As.

with alkalis &c. to form salts. HASO3, H, AsO., H.As,O As,Og Acids not obtained from the oxide

by action of water; oxide is

obtained by heating the acids. No definite acid of Nb, only hydrates

Nb,05.«H,O; Nb,O; Oxide obtained by heating the hy. most salts are complex,

drates; hydrates not obtained may be represented as

directly from the oxide. &Nb,05.yRO where

RO=K,, CaO, &c. HzSb0, (also salts of form Sb,0, Acid not obtained directly from MSb0)

oxide; oxide formed by beating

the acid. HSbO3, H2Sb04, H,Sb,0, Sb,0; Acids not obtained directly from

oxide; oxide formed by heating

the acids. H,Ta,O, (also salts of Ta,0, Acid not obtained directly from form Msa), and various

oxide; oxide produced by heating complex salts

the acid. «Ta,Oz.yRO)

No acids, or salts derived from acids, of didymium, erbium, or bismuth, have been isolated.

* The symbol Aq here signifies that the acid to the formula of which it is added exists only in aqueous solution, and has not been isolated as a solid.

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