Encyclopaedia Britannica Volume 3, Part 1, Slice 1 Part 19

On the outbreak of the first war of independence, d'Azeglio donned the papal uniform and took part under General Durando in the defence of Vicenza, where he was severely wounded. He retired to Florence to recover, but as he opposed the democrats who ruled in Tuscany, he was expelled from that country for the second time. He was now a famous man, and early in 1849 Charles Albert, king of Sardinia, invited him to form a cabinet. But realizing how impossible it was to renew the campaign, and "not having the heart to sign, in such wretched internal and external conditions, a treaty of peace with Austria" (_Correspondance politique_, by E. Rendu), he refused. After the defeat of Novara (23rd of March 1849), Charles Albert abdicated and was succeeded by Victor Emmanuel II. D'Azeglio was again called on to form a cabinet, and this time, although the situation was even more difficult, he accepted, concluded a treaty of peace, dissolved the Chamber, and summoned a new one to ratify it. The treaty was accepted, and d'Azeglio continued in office for the next three years. While all the rest of Italy was a prey to despotism, in Piedmont the king maintained the const.i.tution intact in the face of the general wave of reaction. D'Azeglio conducted the affairs of the country with tact and ability, improving its diplomatic relations, and opposing the claims of the Roman Curia. He invited Count Cavour, then a rising young politician, to enter the ministry in 1850. Cavour and Farini, also a member of the cabinet, made certain declarations in the Chamber (May 1852) which led the ministry in the direction of an alliance with Rattazzi and the Left. Of this d'Azeglio disapproved, and therefore resigned office, but on the king's request he formed a new ministry, excluding both Cavour and Farini. In October, however, owing to ill-health and dissatisfaction with some of his colleagues, as well as for other reasons not quite clear, he resigned once more and retired into private life, suggesting Cavour to the king as his successor.

For the next four years he lived modestly at Turin, devoting himself once more to art, although he also continued to take an active interest in politics, Cavour always consulting him on matters of moment. In 1855 he was appointed director of the Turin art gallery. In 1859 he was given various political missions, including one to Paris and London to prepare the basis for a general congress of the powers on the Italian question. When war between Piedmont and Austria appeared inevitable he returned to Italy, and was sent as royal commissioner by Cavour to Romagna, whence the papal troops had been expelled. After the peace of Villafranca, d'Azeglio was recalled with orders to withdraw the Piedmontese garrisons; but he saw the danger of allowing the papal troops to reoccupy the province, and after a severe inner struggle left Bologna without the troops, and interviewed the king. The latter approved of his action, and said that his orders had not been accurately expressed; thus Romagna was saved. That same year he published a pamphlet in French ent.i.tled _De la Politique et du droit chretien au point de vue de la question italienne_, with the object of inducing Napoleon III. to continue his pro-Italian policy. Early in 1860 Cavour appointed him governor of Milan, evacuated by the Austrians after the battle of Magenta, a position which he held with great ability. But, disapproving of the government's policy with regard to Garibaldi's Sicilian expedition and the occupation by Piedmont of the kingdom of Naples as inopportune, he resigned office.

The death of his two brothers in 1862 and of Cavour in 1861 caused Ma.s.simo great grief, and he subsequently led a comparatively retired life. But he took part in politics, both as a deputy and a writer, his two chief subjects of interest being the Roman question and the relations of Piedmont (now the kingdom of Italy) with Mazzini and the other revolutionists. In his opinion Italy must be unified by means of the Franco-Piedmontese army alone, all connexion with the conspirators being eschewed, while the pope should enjoy nominal sovereignty over Rome, with full spiritual independence, the capital of Italy being established elsewhere, but the Romans being Italian citizens (see his letters to E. Rendu and his pamphlet _Le questioni urgenti_). He strongly disapproved of the convention of 1864 between the Italian government and the pope. The last few years of d'Azeglio's life were spent chiefly at his villa of Cannero, where he set to work to write his own memoirs. He died of fever on the 15th of January 1866.

Ma.s.simo d'Azeglio was a very attractive personality, as well as an absolutely honest patriot, and a characteristic example of the best type of Piedmontese aristocrat. He was cautious and conservative; in his general ideas on the liberation of Italy he was wrong, and to some extent he was an amateur in politics, but of his sincerity there is no doubt. As an author his political writings are trenchant and clear, but his novels are somewhat heavy and old-fashioned, and are interesting only if one reads the political allusions between the lines.

Besides a variety of newspaper articles and pamphlets, d'Azeglio's chief works are the two novels _Ettore Fieramosca_ (1833) and _Niccol dei Lapi_ (1841), and a volume of autobiographical memoirs ent.i.tled _I Miei Ricordi_, a most charming work published after his death, in 1866, but unfortunately incomplete. See in addition to the _Ricordi_, L. Carpi's _Il Risorgimento Italiano_, vol. i. pp. 288 sq. and the _Souvenirs historiques_ of Constance d'Azeglio, Ma.s.simo's niece (Turin, 1884).

(L. V.*)

AZERB[=A]J[=A]N (also spelt ADERBIJAN; the _Azerb[=a]deg[=a]n_ of medieval writers, the _Athropatakan_ and _Atropatene_ of the ancients), the north-western and most important province of Persia. It is separated from Russian territory on the N. by the river Aras (Araxes), while it has the Caspian Sea, Gilan and Khamseh (Zenj[=a]n) on the E., Kurdistan on the S., and Asiatic Turkey on the W. Its area is estimated at 32,000 sq. m.; its population at 1 to 2 millions, comprising various races, as Persians proper, Turks, Kurds, Syrians, Armenians, &c. The country is superior in fertility to most provinces of Persia, and consists of a regular succession of undulating eminences, partially cultivated and opening into extensive plains. Near the centre of the province the mountains of Sahand rise in an acc.u.mulated ma.s.s to the height of 12,000 ft. above the sea. The highest mountain of the province is in its eastern part, Mount Savelan, with an elevation of 15,792 ft., and the Talish Mountains, which run from north to south, parallel to and at no great distance from the Caspian, have an alt.i.tude of 9000 ft. The princ.i.p.al rivers are the Aras and Kizil Uzain, both receiving numerous tributaries and flowing into the Caspian, and the Jaghatu, Tatava, Murdi, Aji and others, which [v.03 p.0081] drain into the Urmia lake. The country to the west of the lake, with the districts of Selmas and Urmia, is the most prosperous part of Azerb[=a]j[=a]n, yet even here the intelligent traveller laments the want of enterprise among the inhabitants. Azerb[=a]j[=a]n is one of the most productive provinces of Persia. The orchards and gardens in which many villages are embosomed yield delicious fruits of almost every description, and great quant.i.ties, dried, are exported, princ.i.p.ally to Russia. Provisions are cheap and abundant, but there is a lack of forests and timber trees. Lead, copper, sulphur, orpiment, also lignite, have been found within the confines of the province; also a kind of beautiful, variegated, translucent marble, which takes a high polish, is used in the construction of palatial buildings, tanks, baths, &c., and is known as Maragha, or Tabriz marble. The climate is healthy, not hot in summer, and cold in winter. The cold sometimes is severely felt by the poor cla.s.ses owing to want of proper fuel, for which a great part of the population has no subst.i.tute except dried cow-dung. Snow lies on the mountains for about eight months in the year, and water is everywhere abundant. The best soils when abundantly irrigated yield from 50- to 60-fold, and the water for this purpose is supplied by the innumerable streams which intersect the province. The natives of Azerb[=a]j[=a]n make excellent soldiers, and about a third of the Persian army is composed of them. The province is divided into a number of administrative sub-provinces or districts, each with a _h[=a]kim_, governor or sub-governor, under the governor-general, who under the Kajar dynasty has always been the heir-apparent to the throne of Persia, a.s.sisted by a responsible minister appointed by the shah. The administrative divisions are as follows:--Tabriz and environs; Uskuh; Deh-Kharegan; Maragha; Miandoab; Sa[=u]jbulagh; Sulduz; Urmia; Selmas; Khoi; Maku; Gerger; Merend; Karadagh; Arvanek; Talish; Ardebil; Mishkin; Khalkh[=a]l; Hashtrud; Garmrud; Afshar; Sain Kaleh; Ujan; Sarab. The revenue amounts to about 200,000 per annum in cash and kind, and nearly all of it is expended in the province for the maintenance of the court of the heir-apparent, the salaries and pay to government officials, troops, pensions, &c.

(A. H.-S.)

AZIMUTH (from the Arabic), in astronomy, the angular distance from the north or south point of the horizon to the foot of the vertical circle through a heavenly body. In the case of a horizontal line the azimuth is its deviation from the north or south direction.

AZO (_c._ 1150-1230), Italian jurist. This Azo, whose name is sometimes written Azzo and Azzolenus, and who is occasionally described as Azo Solda.n.u.s, from the surname of his father, is to be distinguished from two other famous Italians of the same name, viz. Azo Lambertaccius, a canonist of the 13th century, professor of canon law at the university of Bologna, author of _Questiones in jus canonic.u.m_, and Azo de Ramenghis, a canonist of the 14th century, also a professor of canon law at Bologna, and author of _Repet.i.tiones super libro Decretorum_. Few particulars are known as to the life of Azo, further than that he was born at Bologna about the middle of the 12th century, and was a pupil of Joannes Ba.s.sia.n.u.s, and afterwards became professor of civil law in the university of his native town. He also took an active part in munic.i.p.al life, Bologna, with the other Lombard republics, having gained its munic.i.p.al independence. Azo occupied a very important position amongst the glossators, and his _Readings on the Code_, which were collected by his pupil, Alessandro de Santo Aegidio, and completed by the additions of Hugolinus and Odofredus, form a methodical exposition of Roman law, and were of such weight before the tribunals that it used to be said, "Chi non ha Azzo, non vada a palazzo." Azo gained a great reputation as a professor, and numbered amongst his pupils Accursius and Jacobus Balduinus. He died about 1230.

AZO COMPOUNDS, organic substances of the type RN:NR' (where R = an aryl radical and R' = a subst.i.tuted alkyl, or aryl radical). They may be prepared by the reduction of nitro compounds in alkaline solution (using zinc dust and alkali, or a solution of an alkaline stannite as a reducing agent); by oxidation of hydrazo compounds; or by the coupling of a diazotized amine and any compound of a phenolic or aminic type, provided that there is a free para position in the amine or phenol. They may also be obtained by the molecular rearrangement of the diazoamines, when these are warmed with the parent base and its hydrochloride. This latter method of formation has been studied by H. Goldschmidt and R. U. Reinders (_Ber_., 1896, 29, p. 1369), who found that the reaction is monomolecular, and that the velocity constant of the reaction is proportional to the amount of the hydrochloride of the base present and also to the temperature, but is independent of the concentration of the diazoamine. The azo compounds are intensely coloured, but are not capable of being used as dyestuffs unless they contain salt-forming, acid or basic groups (see DYEING). By oxidizing agents they are converted into azoxy compounds, and by reducing agents into hydrazo compounds or amines.

_Azo-benzene_, C_6H_5N:NC_6H_5, discovered by E. Mitscherlich in 1834, may be prepared by reducing nitrobenzene in alcoholic solution with zinc dust and caustic soda; by the condensation of nitrosobenzene with aniline in hot glacial acetic acid solution; or by the oxidation of aniline with sodium hypobromite. It crystallizes from alcohol in orange red plates which melt at 68 C. and boil at 293 C. It does not react with acids or alkalis, but on reduction with zinc dust in acetic acid solution yields aniline.

_Amino-azo Compounds_ may be prepared as shown above. They are usually yellowish brown or red in colour, the presence of more amino groups leading to browner shades, whilst the introduction of alkylated amino groups gives redder shades. They usually crystallize well and are readily reduced. When heated with aniline and aniline hydrochloride they yield indulines (_q.v._). Amino-azo-benzene, C_6H_5N_2C_6H_4NH_2, crystallizes in yellow plates or needles and melts at 126 C. Its const.i.tution is determined by the facts that it may be prepared by reducing nitro-azo-benzene by ammonium sulphide and that by reduction with stannous chloride it yields aniline and meta-phenylene diamine. Diamino-azo-benzene (chrysoidine), C_6H_5N_2C_6H_3(NH_2)_2, first prepared by O. Witt (_Ber._, 1877, 10, p.

656), is obtained by coupling phenyl diazonium chloride with meta-phenylene diamine. It crystallizes in red octahedra and dyes silk and wool yellow.

Triamino-azo-benzene (meta-amin.o.benzene-azo-meta-phenylene diamine or Bismarck brown, phenylene brown, vesuvine, Manchester brown), NH_2C_6H_4N_2C_6H_3(NH_2)_2, is prepared by the action of nitrous acid on meta-phenylene diamine. It forms brown crystals which are readily soluble in hot water, and it dyes mordanted cotton a dark brown. On the composition of the commercial Bismarck brown see E. Tauber and F. Walder (_Ber_., 1897, 30, pp. 2111, 2899; 1900, 33, p. 2116). Alkylated amino-azo-benzenes are also known, and are formed by the coupling of diazonium salts with alkylated amines, provided they contain a free para position with respect to the amino group. In these cases it has been shown by H. Goldschmidt and A. Merz (_Ber_., 1897, 30, p. 670) that the velocity of formation of the amino-azo compound depends only on the nature of the reagents and not on the concentration, and that in coupling the hydrochloride of a tertiary amine with diazobenzene sulphonic acid the reaction takes place between the acid and the base set free by the hydrolytic dissociation of its salt, for the formation of the amino-azo compound, when carried out in the presence of different acids, takes place most rapidly with the weakest acid (H. Goldschmidt and F. Buss, _Ber_., 1897, 30, p. 2075).

_Methyl orange_ (helianthin, gold orange, Mandarin orange), (CH_3)_2NC_6H_4N_2C_6H_4SO_3Na, is the sodium salt of para-dimethylamin.o.benzene-azo-benzene sulphonic acid. It is an orange crystalline powder which is soluble in water, forming a yellow solution.

The free acid is intensely red in colour. Methyl orange is used largely as an indicator. The const.i.tution of methyl orange follows from the fact that on reduction by stannous chloride in hydrochloric acid solution it yields sulphanilic acid and para-aminodimethyl aniline.

_Oxyazo Compounds_.--The oxyazo compounds are prepared by adding a solution of a diazonium salt to a cold slightly alkaline solution of a phenol. The diazo group takes up the para position [v.03 p.0082] with regard to the hydroxyl group, and if this be prevented it then goes into the ortho position. It never goes directly into the meta position.

The const.i.tution of the oxyazo compounds has attracted much attention, some chemists holding that they are true azophenols of the type RN_2R_1OH, while others look upon them as having a quinonoid structure, _i.e._ as being quinone hydrazones, type RNHN:R_1:O. The first to attack the purely chemical side were Th. Zincke (_Ber._, 1883,16, p. 2929; 1884, 17, p. 3026; 1887, 20, p. 3171) and R. Meldola (_Jour. Chem. Soc._, 1889, 55, pp. 114, 603). Th. Zincke found that the products obtained by coupling a diazonium salt with [alpha]-naphthol, and by condensing phenyl-hydrazine with [alpha]-naphthoquinone, were identical; whilst Meldola acetylated the azophenols, and split the acetyl products by reduction in acid solution, but obtained no satisfactory results. K. Auwers (_Zeit. f. phys. Chem._, 1896, 21, p. 355; _Ber._, 1900, 33, p. 1302) examined the question from the physico-chemical standpoint by determining the freezing-point depressions, the result being that the para-oxyazo compounds give abnormal depressions and the ortho-oxyazo compounds give normal depressions; Auwers then concluded that the para compounds are phenolic and the ortho compounds are quinone hydrazones or act as such. A. Hantzsch (_Ber._, 1899, 32, pp. 590, 3089) considers that the oxyazo compounds are to be cla.s.sed as pseudo-acids, possessing in the free condition the configuration of quinone hydrazones, their salts, however, being of the normal phenolic type. J. T.

Hewitt (_Jour. Chem. Soc._, 1900, 77, pp. 99 et seq.) nitrated para-oxyazobenzene with dilute nitric acid and found that it gave a benzene azo-ortho-nitrophenol, whereas quinones are not attacked by dilute nitric acid. Hewitt has also attacked the problem by brominating the oxyazobenzenes, and has shown that when the hydrobromic acid produced in the reaction is allowed to remain in the system, a brombenzene-azo-phenol is formed, whilst if it be removed (by the addition of sodium acetate) bromination takes place in the phenolic nucleus; consequently the presence of the mineral acid gives the azo compound a pseudo-quinonoid character, which it does not possess if the mineral acid be removed from the sphere of the reaction.

Para-oxyazobenzene (benzene-azo-phenol), C_6H_5N:N(1)C_6H_4OH(4), is prepared by coupling diazotized aniline with phenol in alkaline solution.

It is an orange-red crystalline compound which melts at 154 C.

Ortho-oxyazobenzene, C_6H_5N:N(1)C_6H_4OH(2), was obtained in small quant.i.ty by E. Bamberger (_Ber._, 1900, 33, p. 3189) simultaneously with the para compound, from which it may be separated by distillation in a current of steam, the ortho compound pa.s.sing over with the steam. It crystallizes in orange-red needles which melt at 82.5-83 C. On reduction with zinc dust in dilute sal-ammoniac solution, it yields ortho-aminophenol and aniline. Meta-oxyazobenzene, C_6H_5N:N(1)C_6H_4OH(3), was obtained in 1903 by P. Jacobson (_Ber._, 1903, 36, p. 4093) by condensing ortho-anisidine with diazo benzene, the resulting compound being then diazotized and reduced by alcohol to benzene-azo-meta-anisole, from which meta-oxyazobenzene was obtained by hydrolysis with aluminium chloride. It melts at 112-114 C. and is easily reduced to the corresponding hydrazo compound.

_Diazo-Amines._--The diazo-amines, RN:NNHR_1, are obtained by the action of primary amines on diazonium salts; by the action of nitrous acid on a free primary amine, an iso-diazohydroxide being formed as an intermediate product which then condenses with the amine; and by the action of nitrosamines on primary amines. They are crystalline solids, usually of a yellow colour, which do not unite with acids; they are readily converted into amino-azo compounds (see above) and are decomposed by the concentrated halogen acids, yielding haloid benzenes, nitrogen and an amine. Acid anhydrides replace the imino-hydrogen atom by acidyl radicals, and boiling with water converts them into phenols. They combine with phenyl isocyanate to form urea derivatives (H. Goldschmidt, _Ber._, 1888, 21, p. 2578), and on reduction with zinc dust (preferably in alcoholic acetic acid solution) they yield usually a hydrazine and an amine. Diazoamino benzene, C_6H_5N:NNHC_6H_5, was first obtained by P. Griess (_Ann._, 1862, 121, p.

258). It crystallizes in yellow laminae, which melt at 96 C. and explode at slightly higher temperatures. It is readily soluble in alcohol, ether and benzene.

_Diazoimino benzene_, C_6H_5N_3, is also known. It may be prepared by the action of ammonia on diazobenzene perbromide; by the action of hydroxylamine on a diazonium sulphate (K. Heumann and L. Oeconomides, _Ber._, 1887, 20, p. 372); and by the action of phenylhydrazine on a diazonium sulphate. It is a yellow oil which boils at 59 C. (12 mm.), and possesses a stupefying odour. It explodes when heated. Hydrochloric acid converts it into chloraniline, nitrogen being eliminated; whilst boiling sulphuric acid converts it into aminophenol.

_Azoxy Compounds_, R[=NON]R', are usually yellow or red crystalline solids which result from the reduction of nitro or nitroso compounds by heating them with alcoholic potash (preferably using methyl alcohol). They may also be obtained by the oxidation of azo compounds. When reduced (in acid solution) they yield amines; distillation with reduced iron gives azo compounds, and warming with ammonium sulphide gives hydrazo compounds.

Concentrated sulphuric acid converts azoxybenzene into oxyazobenzene (O.

Wallach, _Ber._, 1880, 13, p. 525). Azoxybenzene, (C_6H_5N)_2O, crystallizes from alcohol in yellow needles, which melt at 36 C. On distillation, it yields aniline and azobenzene. Azoxybenzene is also found among the electro-reduction products of nitrobenzene, when the reduction is carried out in alcoholic-alkaline solution.

The mixed azo compounds are those in which the azo group N:N is united with an aromatic radical on the one hand, and with a radical of the aliphatic series on the other. The most easily obtained mixed azo compounds are those formed by the union of a diazonium salt with the pota.s.sium or sodium salt of a nitroparaffin (V. Meyer, _Ber._, 1876, 9, p. 384):

C_6H_5N_2NO_3 + CH_3CH(NO_2)K = KNO_3 + C_6H_5N_2CH(NO_2)CH_3.

Benzene-azo-nitro-ethane.

Those not containing a nitro group may be prepared by the oxidation of the corresponding mixed hydrazo compounds with mercuric oxide. E. Bamberger (_Ber._, 1898, 31, p. 455) has shown that the nitro-alkyl derivatives behave as though they possess the const.i.tution of hydrazones, for on heating with dilute alkalies they split more or less readily into an alkaline nitrite and an acid hydrazide:

C_6H_5NHN:C(NO_2)CH_3 + NaOH = NaNO_2 + C_6H_5NHNHCOCH_3.

Benzene-azo-methane, C_6H_5N_2CH_3, is a yellow oil which boils at 150 C. and is readily volatile in steam. Benzene-azo-ethane, C_6H_5N_2C_2H_5, is a yellow oil which boils at about 180 C. with more or less decomposition. On standing with 60% sulphuric acid for some time, it is converted into the isomeric acetaldehyde-phenylhydrazone, C_6H_5NHN:CHCH_3 (_Ber._, 1896, 29, p. 794).

The diazo cyanides, C_6H_5N_2CN, and carboxylic acids, C_6H_5N_2COOH, may also be considered as mixed azo derivatives. Diazobenzenecyanide, C_6H_5N_2CN, is an unstable oil, formed when pota.s.sium cyanide is added to a solution of a diazonium salt. Phenyl-azo-carboxylic acid, C_6H_5N_2COOH, is obtained in the form of its pota.s.sium salt when phenylsemicarbazide is oxidized with pota.s.sium permanganate in alkaline solution (J. Thiele, _Ber._, 1895, 28, p. 2600). It crystallizes in orange-red needles and is decomposed by water. The corresponding amide, phenyl-azo-carbonamide, C_6H_5N_2CONH_2, also results from the oxidation of phenylsemicarbazide (Thiele, _loc. cit._), and forms reddish-yellow needles which melt at 114 C. When heated with benzaldehyde to 120 C. it yields diphenyloxytriazole, (C_6H_5)_2CN_3C(OH).

AZOIMIDE, or HYDRAZOIC ACID, N_3H, a compound of nitrogen and hydrogen, first isolated in 1890 by Th. Curtius (_Berichte_, 1890, 23, p. 3023). It is the hydrogen compound corresponding to P. Greiss' diazoimino benzene, C_6H_5N_3, which is prepared by the addition of ammonia to diazobenzene perbromide.

Curtius found that benzoyl glycollic acid gave benzoyl hydrazine with hydrazine hydrate:

C_6H_5OCOCH_2COOH + 2N_2H_4H_2O = H_2O + C_6H_5CONHNH_2 + NH_2NHCH_2COOH.

[v.03 p.0083] (Ethyl benzoate may be employed instead of benzoyl glycollic acid for this reaction.) This compound gave a nitroso compound with nitrous acid, which changed spontaneously into benzoylazoimide by loss of water:

C_6H_5CONHNH_2 + HONO = H_2O + C_6H_5CON(NO)NH_2.

C_6H_5CON(NO)NH_2 = H_2O + C_6H_5CON_3.

The resulting benzoylazoimide is easily hydrolysed by boiling with alcoholic solutions of caustic alkalis, a benzoate of the alkali metal and an alkali salt of the new acid being obtained; the latter is precipitated in crystalline condition on standing.

An improved method of preparation was found in the use of hippuric acid, which reacts with hydrazine hydrate to form hippuryl hydrazine, C_6H_5CONHCH_2CONHNH_2, and this substance is converted by nitrous acid into diazo-hippuramide, C_6H_5CONHCH_2CONHN_2OH, which is hydrolysed by the action of caustic alkalis with the production of salts of hydrazoic acid. To obtain the free acid it is best to dissolve the diazo-hippuramide in dilute soda, warm the solution to ensure the formation of the sodium salt, and distil the resulting liquid with dilute sulphuric acid. The pure acid may be obtained by fractional distillation as a colourless liquid of very unpleasant smell, boiling at 30 C., and extremely explosive. It is soluble in water, and the solution dissolves many metals (zinc, iron, &c.) with liberation of hydrogen and formation of salts (azoimides, azides or hydrazoates). All the salts are explosive and readily interact with the alkyl iodides. In its properties it shows some a.n.a.logy to the halogen acids, since it forms difficultly soluble lead, silver and mercurous salts.

The metallic salts all crystallize in the anhydrous condition and decompose on heating, leaving a residue of the pure metal. The acid is a "weak" acid, being ionized only to a very slight extent in dilute aqueous solution.

E. Noelting and E. Grandmougin (_Berichte_, 1891, 24, p. 2546) obtained azoimide from dinitraniline, C_6H_3(NO_2)_2NH_2, by diazotization and conversion of the diazo compound into the perbromide, (NO_2)_2C_6H_3N_2Br_3. This compound is then decomposed by ammonia, dinitrophenylhydrazoate being formed, which on hydrolysis with alcoholic potash gives pota.s.sium hydrazoate (azide) and dinitrophenol. The solution is then acidified and distilled, when azoimide pa.s.ses over. Somewhat later, they found that it could be prepared from diazobenzene imide, provided a nitro group were present in the ortho or para position to the diazo group.

The para-nitro compound is dropped slowly into a cold solution of one part of caustic potash in ten parts of absolute alcohol; the solution becomes dark red in colour and is then warmed for two days on the water bath. After the greater portion of the alcohol has distilled off, the solution is acidified with sulphuric acid and the azoimide distilled over. The yield obtained is only about 40% of that required by theory, on account of secondary reactions taking place. Ortho-nitro-diazobenzene imide only yields 30%.

W. Wislicenus (_Berichte_, 1892, 25, p. 2084) has prepared the sodium salt by pa.s.sing nitrous oxide over sodamide at high temperatures. The acid can also be obtained by the action of nitrous acid on hydrazine sulphate; by the oxidation of hydrazine by hydrogen peroxide and sulphuric acid (A. W.

Browne, _J. Amer. Chem. Soc._, 1905, 25, p. 251), or by ammonium metavanadate (A. W. Browne and F. F. Shetterly, _Abst. J.C.S._, 1907, ii.

p. 863).

_Ammonium azoimide_, N_3NH_4, may be prepared by boiling diazohippuramide with alcoholic ammonia, until no more ammonia escapes, the following reaction taking place:

C_6H_5CONHCH_2CONHN_2OH + 2NH_3 = N_3NH_4 + H_2O + C_6H_5CONHCH_2CONH_2.

The liquid is then allowed to stand for twelve hours, and the clear alcoholic solution is decanted from the precipitated hippuramide. To the alcoholic solution, four times its volume of ether is added, when the ammonium salt is precipitated. It is then filtered, washed with ether, and air-dried. The salt is readily soluble in water, and is only feebly alkaline. It is extremely explosive. _Hydrazine azoimide_, N_5H_5, is also known.

_Chloroazoimide_, ClN_3, the chloride corresponding to azoimide, was obtained by F. Raschig (_Ber._, 1908, 41, p. 4194) as a highly explosive colourless gas on acidifying a mixture of sodium azide and hypochlorite with acetic or boric acid.

AZORES (_Acores_), or WESTERN ISLANDS, an archipelago in the Atlantic Ocean, belonging to the kingdom of Portugal. Pop. (1900) 256,291; area, 922 sq. m. The Azores extend in an oblique line from N.W. to S.E., between 36 55' and 39 55' N., and between 25 and 31 16' W. They are divided into three widely severed groups, rising from a depth of more than 2 m. The south-eastern group consists of St Michael's (So Miguel) and St Mary (Santa Maria), with Formigas; the central, of Fayal (Faial), Pico, St George (So Jorge), Terceira and Graciosa; the north-western, of Flores and Corvo.

[Ill.u.s.tration]

The nearest continental land is Cape da Roca on the Portuguese coast, which lies 830 m. E. of St Michael's; while Cape Cantin, the nearest point on the African mainland, is more than 900 m. distant, and Cape Race in Newfoundland, the nearest American headland, is more than 1000 m. Thus the Azores are the farthest from any continent of all the island groups in the Atlantic; but they are usually regarded as belonging to Europe, as their climate and flora are European in character.