tion and becomes a Referendarius. He then spends at least four years in the practical work of his profession, after which he passes a second examination, and, if he has chosen the bench instead of the bar, becomes an Assessor and is eligible for the position of judge. A lawyer who has passed the necessary examinations may at any time quit the bar for the bench, and a judge is also at liberty to resign his position and enter upon private practice. In all criminal cases the prosecution is undertaken by Government, which acts through Staatsanwälte, or directors of prosecutions, in the pay of

the state.

Perhaps the only item requiring explanation in the above sum mary is the general financial administration under the head of revenue; this includes advances from the surplus in the treasury, Prussia's proportion of the profits of the imperial customs and excises, repayments, interest, and other miscellaneous sources of revenue. The extraordinary expenses included upwards of £450,000 for railways and £750,000 for public works. The total expenditure is rather more than £2 per head of population, while in the United Kingdom it is about £2, 10s. Between 1821 and 1844 the rate in Prussia was 11s. 6d. per head, and even in 1858 it was only 21s. 8d. The incidence of direct taxation in Prussia is also less than in Great Britain, the respective figures being 5s. 3d. and 7s. per head. The principal direct imposts are the income-tax, which brings in 40 per cent. of the whole, the land-tax producing 37 per cent., and the house-tax producing 19 per cent. The proceeds of the incometax amount to about Is. 2d. per head, as compared with 6s. per head in Great Britain (in 1881). The comparative insignificance of the sum raised by indirect taxation is mainly due to the abovenoted fact that the customs-dues and the most important_excise duties have been made over to the imperial exchequer. In the preliminary estimates for 1885-86 the receipts and expenditure are balanced at £62,886,250.

Local taxation in Prussia is often very high. The state incometax is limited to 3 per cent. of the assessed income, but the communes and towns are allowed to make an arbitrary addition for local purposes, sometimes amounting to twice or thrice the sum paid to the state. This is chiefly owing to the fact that the state reserved for itself all taxation on real property, while imposing on the communes the principal share in maintaining the expensive system of public schools. Incomes below £45 (900 marks) are not now taxed, but this exemption is of very recent origin. A few facts from the statistics of taxation and allied subjects may be of interest as affording some slight index to Prussia's growth in prosperity. Between 1864 and 1878 the entire capital subject to income-tax increased from 24 to 48 marks per head of population, while the proportionate number of those liable to the tax had increased by about 75 per cent. It has also been computed that the average income per head increased between 1872 and 1881 by 15 marks, quivalent to a rise of 5 per cent.; that of Great Britain increased in the same period by $83., or 15 per cent. Of all the payers of income-tax in 1872-81 only 0 10 per cent. had incomes of or above £1000, while 43 per cent. had not more than £25 and 52 per cent. between £25 and £100. Between 1867 and 1880 the proceeds of the house-tax increased by over 100 per cent. It now averages 1s. per head, varying from 6d. in country districts up to 5s, or 5s. 6d. in Berlin, Frankfort-on-the-Main, and Cologne. In 1875 the number of depositors in savings banks was 86 per 1000 inhabitants, and by 1880 the number had risen to 107. The sum deposited amounted to £79,643, 400, equivalent to 588. per head of population. At the same date Austria alone of European powers had a higher proportion (678), while in Great Britain the sum was 44s. and in France 278

The public debt of Prussia in 1884 amounted to 3,345,097,438

marks, or £167,254,872. This is equivalent to about £6 per head of population, as compared with three and a half times as much in England. The annual charge for interest on the debt is 5s. 8d. per head in Prussia and 16s. 2d. in England. Between the end of the struggle with Napoleon and 1848 the debt was considerably reduced since 1848 it has steadily increased. It is, however, admirably secured, and a great part of it was incurred in the construction and acquisition of railways, the clear income from which covers the annual charges on the entire debt. The various branches of the debt are being gradually united in a consolidated fund, bearing interest at the rate of 4 per cent. Army and Navy.-The Prussian army now forms about 75 per Army cent. of that of the German empire, of which it also furnished the and model. (See GERMANY.) The first attempt at the foundation of a navy. Prussian navy was made by the Great Elector, who established a small fleet of eight or ten vessels. This, however, was completely neglected by his successors, and the present marine establishment is of quite recent origin. The present imperial navy is simply the Prussian navy under a different name. (See GERMANY.) Bibliography. The statistical facts in the foregoing article have been mainly drawn from the Jahrbuch für die amtliche Statistik des preussischen Staats, the Statistisches Jahrbuch für das deutsche Reich, and other publications of the statistical offices of Prussia and Germany. Good general accounts of the natural, social, and political features of the country are given in Eiselen's Der preussische Staat (Berlin, 1862) and in Daniel's Handbuch der Geographie (5th ed., 1881 sq.). The Prussian constitution and administrative system are concisely described in the Handbuch der Verfassung und Verwaltung in Preussen, by Graf Hue de Grais, and are treated at length in Von Rönne's Staatsrecht der preussischen Monarchie (4th ed., 1881-84). For English readers the most interesting introduction to Prussian history is perhaps still to be found in the first part of Carlyle's Frederick the Great, the not invariably unprejudiced views of which may be corrected by Professor Tuttle's History of Prussia to the Accession of Frederick the Great (Boston, 1884). The latter admirable little work is, indeed, almost indispensable to every English student of Prussian constitutional history. Professor Seeley's Life of Stein (London, 1879) contains an excellent account of Prussia in the Napoleonic period, especially with regard to the important internal reforms carried out at the beginning of the present century. Among the numerous German histories of Prussia two of the best are Droysen's Geschichte der preussischen Politik and Ranke's Zwölf Bücher preussischer Geschichte; the former is authoritative from the writer's copious use of the Prussian archives, but the latter is less diffuse and more interesting. Other standard works are those of Stenzel, Pauli, Riedel, and Lancizolle, while among shorter histories may be mentioned the manual of F. Voigt. Fix's Territorial-Geschichte des brandenburgisch-preussischen Staates, with ten historical maps, is a convenient sketch of the territorial growth of Prussia. The period since the death of Frederick the Great is treated in Förster's Neuere und neueste preussische Geschichte and in Reimann's Neuere Geschichte des preussischen Staats (1882 sq.). The history of the present century is perhaps most fully given in Treitschke's Deutsche Geschichte im neunzehnten Jahrhundert (1879 sq.). Until recently the standard work on the history of Prussia proper was that of Johannes Voigt, but this is now being superseded by Lohmeyer's Geschichte von Ost u. West Preussen (1881 sq.). The latter forms one of an admirable series of provincial histories in course of publication by Perthes of Gotha. The development of the Prussian bureaucracy is traced in Isaacsohn's Geschichte des preussischen Beamtenthums (1870-84). Several points are most satisfactorily handled in the numerous monographs on special periods, the lives of kings and statesmen, (J. F. M.)

and the like.

PRUSSIA, in the original and narrower sense of the word, is a district in the north-eastern corner of the modern kingdom of the same name, stretching along the Baltic coast for about 220 miles, and occupying an area of upwards of 24,000 square miles. The eastern part of this territory formed the duchy of Prussia, which was acquired by the electors of Brandenburg in 1618, and furnished them with their regal title. The western part, which had been severed from the eastern half and assigned to Poland in 1466, was not annexed to Prussia until the partition of Poland in 1772, while the towns of Dantsic and Thorn remained Polish down to 1793. In spite of the contrast between the political and social conditions of the two districts, arising from the difference of their history, they were united in 1824 to form a single province. But, as might have been expected, the union did not work well, and it was dissolved in 1878, giving place to the modern provinces of East and West Prussia. The early history of the whole district is related under the kingdom of PRUSSIA (above) and TEUTONIC ORDER, while the former article also gives (p. 14) some statistics as to the produce of the two provinces.1

EAST PRUSSIA (Ostpreussen), the larger of the two provinces, has an area of 14,280 square miles, and is bounded by the Baltic Sea, Russia, and West Prussia. It shares in the general characteristics of the great north German plain, but, though low, its surface is by no means absolutely flat, as the southern half is traversed by a low ridge or plateau (comp. GERMANY), which attains a height of 1025 feet at a point near the western boundary of the province. This plateau, here named the Prussian Seenplatte, is thickly sprinkled with small lakes, among which is the Spirding See, 46 square miles in extent and the largest inland lake in the Prussian monarchy. 1 Compare Lohmeyer's Geschichte von Ost u. West Preussen (1881, sq.).

The coast is lined with low dunes or sandhills, in front of which lie the large littoral lakes or lagoons named the Frische Haff and the Kurische Haff. (See GERMANY.) The first of these receives the waters of the Nogat and the Pregel, and the other those of the Memel or Niemen. East Prussia is the coldest part of Germany, its mean annual temperature being about 44° Fahr., while the mean January temperature of Tilsit is only 25°. The rainfall is 24 inches per annum. About half the province is under cultivation; 18 per cent. is occupied by forests, and 23 per cent. by meadows and pastures. The most fertile soil is found in the valleys of the Pregel and the Memel, but the southern slopes of the Baltic plateau and the district to the north of the Memel consist in great part of sterile moor, sand, and bog. The chief crops are rye, oats, and potatoes, while flax is cultivated in the district of Ermland, between the Passarge and the upper Alle. East Prussia is the headquarters of the horse-breeding of the country and contains the principal Government stud of Trakehnen; numerous cattle are also fattened on the rich pastures of the river-valleys. The extensive woods in the south part of the province harbour a few wolves and lynxes, and the elk is still preserved in the forest of Ibenhorst, near the Kurische Haff. The fisheries in the lakes and haffs are of some importance; but the only mineral product of note is amber, which is found in the peninsula of Samland in greater abundance than in any other part of the world. Manufactures are almost confined to the principal towns, though linen-weaving is practised as a domestic industry. Commerce is facilitated by canals connecting the Memel and Pregel and also the principal lakes, but is somewhat hampered by the heavy dues exacted at the Russian frontier. A brisk foreign trade is carried on through the seaports of Königsberg (140,909), the capital of the province, and Memel (19,660), the exports consisting mainly of timber and grain. In 1880 the population of East Prussia was 1,933,936, including 1,654,510 Protestants, 250, 462 Roman Catholics, and 18,218 Jews. The Roman Catholics are mainly confined to the district of Ermland, in which the ordinary proportions of the confessions are completely reversed. The bulk of the inhabitants are of German blood, but there are 400,000 Protestant Poles (Masurians or Masovians) in the south part of the province, and 150,000 Lithuanians in the north. As in other provinces where the Polish element is strong, East Prussia is below the general average of the kingdom in education; in 1883 fully 51 per cent. of its recruits were unable to read or write. There is a university at Königsberg.

WEST PRUSSIA (Westpreussen), with an area of 9850 square miles, is bounded by the Baltic, East Prussia, Poland, Posen, Brandenburg, and Pomerania. It resembles East Prussia in its physical characteristics, but its fertility is somewhat greater and its climate not quite so harsh. The Baltic plateau traverses the province from east to west, reaching its culminating point in the Thurmberg (1090 feet), near Dantsic. Near the middle of the province the range is interrupted by the valley of the Vistula, beyond which it trends to the north and approaches the coast. The lakes of West Prussia are nearly as numerous but not so large as those of the sister province. The natural products are similar, and the manufactures are also almost confined to the large towns. The cultivation of the common beet, for the production of sugar, has been introduced, and several sugar refineries have been erected. The valley of the Vistula, particularly the rich lowlands (Werder) of the delta, are very fertile, producing good crops of wheat and pasturing large herds of horses, cattle, and sheep. The population in 1880 was 1,405,898, consisting in almost equal proportions of Roman Catholics and Protestants; there were 26,547 Jews and 490,000 Poles. The percentage of illiterate recruits in 1882 was still higher than in East Prussia (7 97), but not so high as in Posen (9.75). The capital and principal town is Dantsic (108,551), while Elbing (35,842) and Thorn (20,617) also carry on a considerable trade.

PRUSSIA, RHENISH (German, Rheinpreussen, Rheinprovinz, Rheinland), the most westerly province of the kingdom of Prussia, is bounded on the N. by Holland, on the E. by Westphalia, Hesse-Nassau, and Hesse-Darmstadt, on the S.E. by the Rhenish Palatinate, on the S. and S.W. by Lorraine, and on the W. by Luxemburg, Belgium, and Holland. The small district of Wetzlar in the midst of the province of Hesse also belongs to Rhenish Prussia, which, on the other hand, surrounds the Oldenburg principality of Birkenfeld. The extent of the province is 10,420 square miles, or nearly twice that of the kingdom of Saxony; its extreme length, from north to south, is nearly 200 miles and its greatest breadth is just under 90. It includes about 200 miles of the course of the Rhine, which forms the eastern frontier of the province from Bingen to Coblentz and then flows through it in a north-westerly direction.

The southern and larger half of Rhenish Prussia, belong ing geologically to the Devonian formations of the lower Rhine, is hilly. On the left bank are the elevated plateaus of the Hundsrück and the Eifel, separated from each other by the deep valley of the Moselle, while on the right bank are the spurs of the Westerwald and the Sauerland, the former reaching the river in the picturesque group known as the Seven Mountains. The highest hill in the province is the Walderbeskopf (2670 feet) in the Hochwald, and there are several other summits above 2000 feet on the left bank, while on the right there are few which attain a height of 1600 feet. Most of the hills are covered with trees, but the Eifel is a barren and bleak plateau, with numerous traces of volcanic agency, and is continued towards the north-west by the moorlands of the Hohe Venn. To the north of a line drawn from Aix-la-Chapelle to Bonn the province is flat, and marshy districts occur near the Dutch frontier. The climate varies considerably with the configuration of the surface. That of the northern lowlands and of the sheltered valleys is the mildest and most equable in Prussia, with a mean annual temperature of 50° Fahr., while on the hills of the Eifel the mean does not exceed 44°. The annual rainfall varies in the different districts from 18 to 32 inches. Almost the whole province belongs to the basin of the Rhine, but a small district in the north-west is drained by affluents of the Meuse. Of the numerous tributaries which join the Rhine within the province, the most important are the Nahe, the Moselle, and the Ahr on the left bank, and the Sieg, the Wupper, the Ruhr, and the Lippe on the right. The only lake of any size is the Laacher See, the largest of the " maare or extinct crater lakes of the Eifel.

The

Of the total area of the Rhenish province about 46.5 per cent. is occupied by arable land, 17 per cent. by meaLittle dows and pastures, and 31 per cent. by forests. except oats and potatoes can be raised on the high-lying plateaus in the south of the province, but the river-valleys and the northern lowlands are extremely fertile. great bulk of the soil is in the hands of small proprietors, and this is alleged to have had the effect of somewhat retarding the progress of scientific agriculture. The usual cereal crops are, however, all grown with success, and tobacco, hops, flax, rape, hemp, and beetroot (for sugar) are cultivated for commercial purposes. Large quantities The vine-culture occupies a of fruit are also produced. space of 30,000 acres, about half of which are in the valley of the Moselle, a third in that of the Rhine itself, and the The choicest rest mainly on the Nahe and the Ahr. varieties of Rhine wine, however, such as Johannisberger and Steinberger, are produced higher up the river, beyond the limits of the Rhenish province. the limits of the Rhenish province. In the hilly districts more than half the surface is sometimes occupied by forests, and large plantations of oak are formed for the use of the bark in tanning. Considerable herds of cattle are reared on the rich pastures of the lower Rhine, but the number of sheep in the province is comparatively small, and is, indeed, not greatly in excess of that of the goats. wooded hills are well stocked with deer, and a stray wolf occasionally finds its way from the forests of the Ardennes into those of the Hundsrück. The salmon fishery of the Rhine is very productive and trout abound in the mountain streams. (Compare the agricultural tables under PRUSSIA, p. 14 supra.)

The

Besides

The great mineral wealth of the Rhenish province probably furnishes its most substantial claim to the title of the "richest jewel in the crown of Prussia." parts of the Carboniferous measures of the Saar and the Ruhr, it also contains important deposits of coal near Aix-la-Chapelle. Iron occurs abundantly near Coblentz, the Bleiberg in the Eifel possesses an apparently inex

are derivatives of a blue pigment which was discovered accidentally by Diesbach, a Berlin colourmaker, about the beginning of the 18th century.

The foundations of our present knowledge of cyanides were laid by Scheele (1783), whose discoveries were subsequently (from 1811) confirmed and supplemented, chiefly in the sense of quantitative determinations, by Gay-Lussac. Although we have no space for further historical notes, we must not omit to state that Gay-Lussac, as one result of his work, conceived and introduced into chemistry the notion of the "compound radical," having shown that prussic acid and its salts are related to the group NC in precisely the same way as chlorides are to chlorine, or sulphides to sulphur. This idea, in his own eyes and in those of his contemporaries, was greatly fortified by his success in even isolating his "cyanogène" as a substance.

In preparing cyanogen or cyanides in the laboratory the operator now always starts from prussiate of potash, with which, accordingly, we begin.

Prussiate of Potash, (NC) Fe. K1+3H2O (syn. ferrocyanide of potassium; Germ. Blutlaugensalz). This salt is being produced industrially from animal refuse (hide and horn clippings, old shoes, blood solids, &c.), carbonate of potash, and iron filings or borings as raw materials. The carbonate of potash is fused at a red heat in an iron pear-shaped vessel suspended within a furnace, or on the cupel-shaped sole of a reverberatory furnace, and the animal matter, which should be as dry as possible, is then introduced in instalments along with the iron. The fusion is continued as long as inflammable gases are going off; then the still fluid mass is ladled out and allowed to cool, when it hardens into a black stone-like body known to the manufacturer as "metal." When the brokenup metal is digested with water in an iron vessel prussiate of potash passes into solution, while a black residue of charcoal, metallic iron, sulphide of iron, &c., remains. The clarified solution, after sufficient concentration in the heat, deposits on cooling part of its prussiate in lemon-yellow quadratic crystals (generally truncated octahedra), which are purified by recrystallization. The last mother-liquors furnish an impure green salt, which is added to a fresh fuse and so utilized.

In former times it was believed that the prussiate was produced during the fusion process, and in the subsequent process of lixiviation simply passed into solution, until Liebig showed that this view was untenable. The fuse cannot contain ready-formed prussiate, because this salt at a red heat breaks up with formation of a residue of carbide of iron and cyanide of potassium. The metal in fact when treated with dilute alcohol gives up to it plain cyanide of potassium, and the fully exhausted residue yields no prussiate on treatment with water. The prussiate accordingly must be produced during the process of lixiviation by the action of the cyanide of potassium on some ferrous compound in the metal. Liebig thought that it was partly the metallic iron, partly the sulphide of iron present in the metal, which effected the conversion. According to more recent researches a double sulphide, K,S+ FeS, which is always produced during the fusion (from the reagents proper and the sulphur of the organic matter and that of the sulphate of potash present in the carbonate as an impurity), plays this important part. The double sulphide by the action of water breaks up into alkaline sulphide, sulphide of iron (FeS), and sulphur. This sulphide of iron is of a peculiar kind; it does what ordinary FeS does not effect, readily at least: it converts the cyanide into prussiate, thus, 6NC.K+ FeS=K,S+ (NC) Fe. K4, while the eliminated sulphur of the original FeS unites with another part of the cyanide of potassium into sulphocyanate, S+NCK SNC. K, which latter salt is thus unavoidably produced as a (rather inconvenient) byeproduct. Pure prussiate of potash has the specific gravity 1.83; it is permanent in the air. It loses its water, part at 60° C., the rest at 100° C., but very slowly. The anhydrous salt is a white powder. The crystals dissolve in four parts of cold and in two parts of boiling water. It is insoluble in, and not dehydrated by, alcohol. Prussiate of potash has the composition of a double salt, Fe(NC),+4KNC, but the idea that it contains these two binary cyanides is entirely at variance with its reactions. Cyanide of potassium is readily decomposed by even the feeblest acids, and to some extent even by water, with elimination of hydrocyanic acid, and on this account perhaps is intensely poisonous. A solution of the prussiate remains absolutely unchanged on evaporation, and the action on it even of strong acids in the cold results in the formation of the hydrogen salt, (NC) FeH4, which is decomposed, it is true, but only when the mixture is heated, with evolution of hydrocyanic acid. It is not poisonous. Its solution when mixed with nitrate of silver does not give a precipitate of cyanide of silver, NC. Ag, and a solution of the two nitrates, but yields a unitary pre

cipitate of the composition (NC), Fe.Ag, which contains all the iron; only nitrate of potassium passes into solution. Other heavy metallic salts behave similarly. On the strength of these considerations chemists, following the lead of Liebig, view prussiate as a binary compound of potassium, K4, with a complex radical, NC.Fe, "ferrocyanogen.

Hydrocyanic Acid, NC.H.-This acid is prepared most confollowing method. Ten parts of powdered prussiate are placed in a Wöhler recommends the veniently from prussiate of potash. retort, the neck of which is turned upwards, and a (cooled down) mixture of seven parts of oil of vitriol and fourteen parts of water is then added. If the aqueous acid is wanted, the exit-end of the retort is joined on direct to a Liebig's condenser, which must be kept very cool by a current of cold water. If the anhydrous acid is desired, two wide-necked bottles (or two large U-tubes) charged with fused chloride of calcium and kept at 30° C. by immersion in a water bath of this temperature, must be inserted between the retort and condenser. In this case more particularly it is indispensable to provide for a most efficient condensation of the vapours; the exitend of the condenser should be provided with an adapter going down to near the bottom of the receiver, which must be surrounded by a freezing mixture. The temperature of the latter, of course, must not be allowed to fall to the freezing-point of the distillate. The retort is heated by means of a sand bath and a brisk distillation maintained until the residue begins to dry up. The result of the reaction is in accordance with the assumption that the dilute vitriol, in the first instance, converts the prussiate, one-half into (NC) Fe.H, the other into (NC) Fe. K2H, and that through the effect of the heat these two bodies decompose each other into {(NC), Fe} K,Fe, which remains in the residue as a precipitate, and (NC)&H=6NCH, which distils over. Real NCH is a colourless liquid of 0.6967 specific gravity at 18° C., which freezes at -15° C. (Gay-Lussac) into a white fibrous solid. According to Schulz the acid, if really pure, remains liquid at 37° C. It boils at 26°5 C.; at 4°.5 its vapour-tension already amounts to half an atmosphere. The vapour is inflammable and burns into carbonic The acid mixes with water in all acid, water, and nitrogen. proportions, with contraction and yet absorption of heat. The solution behaves on distillation like a mere mechanical mixture of its two components. Prussic acid has a very peculiar powerful smell; more characteristic still is a kind of choking action which even the highly attenuated vapour exerts on the larynx. Prussic acid is fearfully poisonous; a few drops of even the ordinary pharmaceutical preparation (of 2 per cent.) are sufficient to kill a large dog. It acts with characteristic promptitude, especially when Even a relatively large dose, if it has once safd to do relatively little harm there.1 found its way into the stomach without producing a fatal effect, is

inhaled as a vapour.

Prussic acid is characteristically prone to suffer "spontaneous decomposition. Whether the pure anhydrous acid really is, in the strictest sense of the word, still requires to be found out; the and turbid from "azulmic" acid, a substance of complex constituordinary preparation, when kept in a close bottle, soon turns brown acid is liable to similar changes; in its case formiate of ammonia tion. Other things are formed at the same time. The pure aqueous always forms the predominant product. This change is easily understood

NC. H+2H20=NH3+H. COOH.

Ammonia. Formic acid.

A strong aqueous prussic acid, when mixed with fuming hydrochloric acid, is soon converted into a magma of crystals of salammoniac, with formation of formic acid, which remains dissolved. And yet, most singularly, the addition to the preparation of a small proportion of hydrochloric or sulphuric acid is the best means for preventing, or at least greatly retarding, its spontaneous change in the very same direction. Aqueous prussic acid acts only very feebly (if at all) on blue litmus; it combines with aqueous caustic alkalis but does not decompose their carbonates; nor does it act upon the generality of insoluble basic metallic oxides or hydrates; mercuric oxide and oxide of silver form noteworthy exceptions to this rule.

Cyanogen, (NC),.-When dry mercuric cyanide is heated it breaks up, below redness, into mercury and cyanogen gas; part of the latter, however, always suffers polymerization into a solid called Cyanogen gas is colourless; it has the specific gravity demanded by paracyanogen," and presumed to consist of molecules (NC)3. its formula. It possesses a peculiar odour and has a characteristic

1 The British Pharmacopoeia prescribes for the medicinal acid a strength of 2 per cent. of real NCH. The two medicinal preparations known as aqua amygdalarum amararum and as aqua laurocerasi respectively contain prussic acid in combination with hydride of benzoyl, CH.COH. In neither case does the prussic acid pre-exist in the vegetable materials, but is produced during the mashing process which precedes the distillation, by a fermentative decomposition of the amygdalin which they contain. (See FERMENTATION, vol. ix. p. 96.)

1

0°

+20° C. 5 atmos.

irritating effect on the eyes and mucous membranes of the nose. It is poisonous. By strong pressure it is condensible into a liquid which freezes at -34°4 C., and has the following vapour-tensions Pat the temperatures t statedt = - 20°.7 -10° +10° P= 1.85 2.7 3.8 At ordinary temperatures water dissolves about 4.5 times, alcohol about 23 times its volume of the gas. The solutions are liable to (very complex) spontaneous decomposition. The list of products includes oxalate of ammonia and urea. Cyanogen burns with a characteristically beautiful peach-blossom coloured flame into carbonic acid and nitrogen. This gas cyanogen, as already stated, is to cyanides what chlorine gas Cl is to chlorides, but it is well to remember that the analogy, though perfect in regard to the corre sponding formulæ, does not, as a rule, extend to the conditions of formation of the bodies represented. Thus cyanogen does not unite with hydrogen into prussic acid, nor does it combine with ordinary metals in the chlorine fashion. When passed over heated potassium, it is true, it combines with it into cyanide; and caustic potash-ley absorbs it with formation of cyanide and cyanate (NCO.K), just as chlorine yields chloride and hypochlorite KCIO; but this is about the sum-total of the analogies in action. Yet metallic cyanides of all kinds can be produced indirectly.

Cyanide of Potassium, NC.K.-An aqueous mixture of the quantities NCH and KHO no doubt contains this salt, but it smells of the acid, and on evaporation behaves more like a mixture of the two congeners than in any other way. An exhaustive union can be brought about by passing NCH vapour into an alcoholic solution of KHO; the salt NC. K then comes down as a crystalline precipitate, which must be washed with alcohol and dried, cold, over vitriol. A more convenient method is to dehydrate yellow prussiate and then decompose it by heating it to redness in an iron crucible. The Fe(NC), part of the salt breaks up into cyanogen and nitrogen, which go off, and a carboniferous finely-divided iron, which remains, with cyanide of potassium, which at that temperature is a thin fluid. Yet the iron sometimes refuses to settle with sufficient promptitude to enable one to decant off the bulk even of the fused cyanide. According to private information received by the writer a French manufacturer uses a certain kind of very porous fireclay as an efficient filtering medium.

The ordinary "cyanide of potassium" of trade is not strictly that at all, but at best a mixture of the real salt with cyanate. It is produced by fusing a mixture of eight parts of anhydrous prussiate and three parts of anhydrous carbonate of potash, allowing the

reaction

(NC),Fc. K ̧+K2CO2=CO2+Fe+5NCK+K.NCO

Cyanate.

unites not only with other cyanides but also with a multitude of other salts into crystallizable double salts. Mercurous cyanide, Hg(NC)2, seems to have no existence. When it is attempted to produce it by double decompositions, the mixture Hg+(NC),Hg comes forth instead of the compound Hg(NC). (4) Heavy metallic cyanides are mostly insoluble in water, and the general method for their preparation is to decompose a solution of the respective sulphate, chloride, &c., with one of cyanide of potassium. The most important general property of these bodies is that they readily dissolve in solution of cyanide of potassium with formation of double cyanides, which in their capacity as double salts all exhibit, in a higher or lower degree, those anomalies which were fully explained above (see “prussiate of potash "). These "metallocyanides," as we will call them, being all, unlike plain cyanide of potassium, very stable in opposition to water and aqueous alkalis, are readily produced from almost any compound of the respective metallic radical-some from the metal itself-by treatment with solution of cyanide of potassium. In all we have said "potassium" may be taken as including sodium and in a limited sense ammonium, but the potassium compounds are best known, and we accordingly in the following section confine ourselves to these. Metallo-cyanides.-(1) Silver.-Cyanide of silver, Ag. NC, is produced as a precipitate by addition of hydrocyanic acid or cyanide of potassium to solution of nitrate of silver. The precipitate is similar in appearance to chloride of silver and, like it, insoluble in cold dilute mineral acids, but soluble in ammonia. At a red heat it is decomposed with formation of a residue of carboniferous metallic silver. Precipitated cyanide of silver, though insoluble in hydrocyanic acid, dissolves readily in cyanide of potassium with formation of argentocyanide, AgK. (NC)2, which is easily obtained in crystals, permanent in the air and soluble in eight parts of cold water. Chloride of silver dissolves in cyanide of potassium solution as readily as the cyanide does and with formation of the same double saltAgCl+2KNC= KCl+AgK(NC)2. This salt is used very largely in electro-plating (2) Lead. From a solution of the acetate cyanide of lead is precipitated by addition of hydrocyanic acid or cyanide of potassium. The precipitate, Pb(NC), has the exceptional property of being insoluble in cyanide of potassium. (3) Zinc.Cyanide of zinc, Zn(NC),, is obtained by addition of hydrocyanic acid to a solution of the acetate, as a white precipitate readily soluble in cyanide of potassium with formation of a double salt, ZnK(NC), which forms well-defined crystals. (4) Nickel.-The cyanide, Ni(NC), is an apple-green precipitate, which is obtained by methods similar to those given under "zinc. It readily dissolves in cyanide of potassium with formation of a crystallizable salt, NiK(NC)+H2O, the solution of which is stable in air and not convertible into one of a nickelic (Ni"") compound by chlorine (compare "cobalt" infra). The potassio-cyanides of silver, zinc, and nickel as solutions are not changed visibly by caustic alkalis, but their heavy metals can be precipitated by sulphuretted hydrogen or sulphide of ammonium, as from solutions of, for instance, the chlorides. Aqueous mineral acids (in the heat at least) decompose them exhaustively with elimination of all the NC as NCH. (5) Copper.-When cyanide of potassium solution is added to one of sulphate of copper, a yellow precipitate of cupric cyanide, Cu(NC), comes down; but on boiling this precipitate loses cyanogen and is converted into a white precipitate of the cuprous salt Cu(NC). This white precipitate dissolves in cyanide of potassium with formation chiefly of two crystalline double salts, viz., CuNC+6NCK, easily soluble in water, and CuNC+NCK. The latter is decomposed by water with elimination of Cu. NC. The solution of the 6NC. K salt is not precipitated by sulphuretted hydrogen. Solutions of potassio-cyanides of cuprosum are used in electro-plating. (6) Gold.-Metallic gold dissolves in cyanide of potassium solution in the presence of air, thus

1

Au+ 2KNC+10= |K,O + AuK. (NC) This auro-cyanide of potassium is used largely for electro-gilding, for which purpose it is conveniently prepared as follows. Six parts of gold are dissolved in aqua regia and the solution is precipitated by ammonia. The precipitate (an explosive compound known as "fulminating gold ") is dissolved in a solution of six parts of cyanide of potassium, when the double salt is formed with evolution of ammonia. The salt crystallizes in rhombic octahedra, soluble in seven parts of cold water.

In the following potassio-cyanides the heavy metals cannot be detected by means of their ordinary precipitants; these salts all behave like the potassium salts of complex radicals composed of the heavy metal and all the cyanogen. (7) Cobalt.-Cyanide of potassium when added to a solution of a cobaltous salt (CoCl,, &c.) gives a precipitate soluble in excess of reagent. The solution presumably contains a cobalto-cyanide, Co(NC).KNC, but on exposure to air eagerly absorbs oxygen with formation of cobalti-cyanide, thusCo(NC),+4KNC + }0= }K2O+Co"(NC), . 3KNC. Chlorine (Cl instead of 10) acts more promptly with a similar effect. If the alkaline solution is acidified and boiled, the same cobalticyanide is produced with evolution of hydrogen

Co(NC)2+4KNC + HCl = KCl + }H, +Co”(NC),. 3KNC.