Hyponitrous acid (HNO) and nitrous acid (HNO,) act as reducing agents; they readily combine with oxygen to produce nitric acid. Nitric acid on the other hand is very frequently used as an oxidiser; when heated it is decomposed to water, oxygen, and nitrogen dioxide (2HNO, H2O+ 2NO, + O). All the nitrogen acids are monobasic. = 2 3 When aqueous solutions of hypophosphorous acid (H,PO, and phosphorous acid (H,PO) are boiled, phosphine (PÅ1) is evolved, and phosphoric acid (H,PO) remains in solution. The three phosphoric acids, ortho- HPO, meta- HPO,, and pyro- HP,O,, may be formed by adding water to phosphoric anhydride PO, (s. Chap. XI., par. 215). Hypophosphorous acid is monobasic, and phosphorous acid is dibasic. Of the three phosphoric acids, orthophosphoric H,PO1 forms the largest number of definite salts: sodium pyrophosphate, Na P,O,, is obtained by heating ordinary sodium phosphate (2Na,HPO = H2O + Na P,O,); sodium metaphosphate, NaPO,, may be obtained by heating sodium-ammonium phosphate (Na(NH)HPO1 = H2O + NH2+ NaPO1). When orthophosphoric acid is heated to 230° or so pyrophosphoric acid is obtained (2H,PO, H2O+ HP,O,), at a red heat metaphosphoric acid is produced (HPO = H2O+HPO2). When metaor pyro-phosphoric acid is boiled with water orthophosphoric acid is produced. 2 = 2 2 2 4 2 Metavanadic acid HVO, and pyrovanadic acid H ̧V,O,, are prepared, indirectly, from salts of these acids. Besides the salts of these acids, numerous polyvanadates (or condensed vanadates) exist; the following are given as examples, Na VO,,, SrVO 2 ვა 16 "No arsenious acid has been isolated. An aqueous solution of arsenious oxide (As,O) may contain arsenious acid; when this solution is neutralised with soda the salt NaAsO, is obtained; by adding silver nitrate to an aqueous solution of As,O,, Ag,ASO, is precipitated. The arsenites are unstable salts, their composition seems to change with small variations in the conditions of their formation. Arsenic acid, H ̧AsO1 is formed by oxidising As,O, in presence of water, either by nitric acid or by chlorine, and crystallising. This acid loses water at 150° or so with formation of pyro-arsenic acid (2H,ASO, H2O+H,As,O,), and at about 210° water is again. evolved and meta-arsenic acid remains 4 = 2 3 (H ̧As ̧0, = H ̧0 + 2HAsO ̧). Both meta- and pyro-arsenic acids are at once changed to the ortho-acid by solution in water. Antimonious oxide dissolves in hot caustic soda solution; from this solution the salt NaSbO, is obtained on cooling. Ortho-antimonic acid H,SbO, is produced, indirectly, from tartar emetic, KSbC,H,O,. The antimonites are easily oxidised; they are unstable and easily undergo change. Antimonic acid, H,SbO, is obtained by adding a little water to SbCl, and drying the solid thus obtained over sulphuric acid; at 100° water is evolved and pyro-antimonic acid, H Sb,O,, remains, and at 200° this acid again loses water with production of meta-antimonic acid, HSbO, These acids seem all to exist in aqueous solution; salts derived from HSbO, and HSb,O,, but not from H,SbO,, are known. 2 ვა 432 Salts are obtained by replacing the hydrogen of various acids by the elements vanadium, didymium, erbium, or bismuth. The salts of didymium and erbium have not been much studied; they seem to belong to the form M,3X, where X=SO, 2NO, &c. Vanadium pentoxide, V.O, interacts with alkalis to produce salts of the form M,VO; but it also interacts with sulphuric acid, and with a few other acids, to produce basic salts, e.g. (VÓ),(SO), Vanadium tetroxide, V,O,, also interacts with sulphuric acid to form the salt vo.so. 2 49 Bismuthous oxide, Bi̟,O,, forms a series of salts by interacting with acids; these salts belong to the form Bi̟,3X (X=SO, 2NO,, PO, &c.), e.g. Bi̟,3ŠO, Bi̟6NO, BiPO BiAsO Most of these salts are decomposed by water with formation of basic salts; the composition of some of these basic salts is represented by the general formula BiOX where X=NO,, SO &c.; but many others are more complex, and their composition can be expressed only by such a formula as xBi̟ O̟.yR.zHO where Ran acidic oxide, e.g. N ̧O,, SO,, 2 &c. 2 3 2 3 433 The elements of Group V. shew a gradual change of properties from the decidedly negative nitrogen to the metallic bismuth. Various small sub-classes appear in the group; thus arsenic and antimony are very closely related; so are niobium and tantalum; nitrogen and phosphorus also are very similar in many chemical properties. Vanadium appears to be more distinctly, metallic in its chemical properties than the elements which succeed it in the even-series, but it is to be remembered that the properties of these elements have been very imperfectly investigated. The group cannot be divided into two families comprising the even-series and odd-series elements, respectively. Although it cannot be said that all the elements shew marked similarities, yet the group-character is impressed on them all. All the elements of this group are distinctly more like each other than they are like the elements of any other group. Group I. presents a number of elements some of which are very similar in their chemical properties, while others are so different from these and from one another that it seems at first sight quite a mistake to place them in the same group. 434 Even-series elements, and second member of oddseries Atomic weights 23 39.04 132.7 7.01 The molecular weights of sodium and potassium are the same as their atomic weights; the other elements of the family have not yet been gasified, and therefore their molecular weights are unknown. 5 9 11 Au=197 SODIUM. POTASSIUM. RUBIDIUM. CAESIUM. 85.2 Sp. grs. (approx.) *59 1.52 58° 62° 38° 1-88 26°-27° Silicate and Compounds are 23.5 *293 Silver-white; soft; very ductile at 0°; can be distilled at redheat. Chloride, sili- Prepared by Oxidises rapidly in air. Decomposes cold water rapidly with evolution of H and production of NaOHAq. These metals all combine directly and rapidly with the halogens, and with sulphur. The following compounds of these metals have been gasified and their molecular weights determined, KI, RыI, RыCl, RbI, CsCl, CsI; in these molecules the atoms of potassium, rubidium, and caesium are monovalent. The five elements we are now considering form the family 436 of alkali metals; the prominent chemical characteristics of these metals have been already examined in Chap. XI. pars. 163-168. It will suffice to summarise these characteristics here. Oxides and hydroxides, MO and MOH, are strongly basic and alkaline; very soluble in water, M2O forming MOHAq. The hydroxides are formed at ordinary temperatures by direct interaction of oxides MO with water; they are not decomposed by heat alone. Oxides of rubidium and caesium have not yet been isolated. The oxides Na ̧O, KO,, and a few others, are known. 2 Sulphides and hydrosulphides, MS and MSH, are strongly basic; they interact with many more negative sulphides to form thio-salts. No sulphide of rubidium or caesium has yet been isolated. M,S,, MS, MS, MS, are known, where M = Na or K. Haloid compounds, MX, are very stable solids, soluble in, and not decomposed by, water. The chlorides, except LiCl, form many double compounds with chlorides of less positive elements, e.g. PtCl. 2MC1; SbCl. 6MC1. Salts, M.X where X = SO,, 2NO,, CO, 2C10,, PO, &c. are very definite, stable, bodies; very few basic salts exist. Many of the salts combine with similar salts of less positive elements forming double salts; the alums M,SO.X 3SO.24H,O are important (X = Al, Cr, Fe, Ga, In). Lithium does not form an alum. Most of the salts are easily soluble in water. Lithium is less like the other members of the family than they are like each other. LiOH is much less soluble in water than the other hydroxides; Li,CO, and Li ̧PO, are also much less soluble than the other carbonates and phosphates; Li,SO, does not combine with Al,. 3SO,, a double salt 3Li,SO. Cr ̧(SO4), is known, but it is not an alum. All the elements of the family except lithium form sulphates of the form MHSO,; Li,H,(SO), is known. 4 The odd-series elements of Group I. shew great differences 437 |