Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/719

Rh in Wallachia. He studied at Buda and Padua, and became teacher of the children of the Wallachian prince Mourousi. After the fall of that prince in 1811, he was employed by Prince Caradja, who had been appointed hospodar of Moldavia and Wallachia, in drawing up a code of laws for that country. On the removal of Caradja, he retired into private life and gave himself to literature. He wrote drinking songs and love ditties which are very popular among the Greeks. He is also the author of a tragedy, of Parallela (a comparison of various systems of govern ment), of translations of Homer and Herodotus, and of some philological works on the connection between ancient and modern Greek.  CHROMIUM, one of the metallic chemical elements, so called from the Greek ^pw/xa, colour, in allusion to the fine colours of its compounds ; symbol Cr, atomic weight 52 4. It does not occur in the free state or very abundantly in nature. It is a constituent of the minerals chrome iron stone, Cr 2 Fe0 4 ; chrome-ochre, Cr 2 O 3 ; ouvarovite, or chrome garnet, Si 3 CaCr ? O 10 ; crocoisite, PbCrO 4, in which it was discovered by Vauquelin in 1797 ; of Vauquelinite, a chromate of lead and copper ; and of some iron-ores and meteoric irons; and it is the cause of the colour of green serpentine, pyrope, and the emerald. The properties of chromium vary much according to the method of its pre paration. By Wohler s process of reducing the sesqui oxide with zinc, it is obtained as a shining green powder, of specific gravity 6 81, which tarnishes in the air, and dissolves in hydrochloric and warm dilute sulphuric acid, but is not acted on by strong nitric acid. Deville, by intensely igniting chromic oxide with sugar-charcoal in a lime crucible, procured chromium of a bright steel-grey colour, very hard, capable of a high polish, less fusible than platinum, and of specific gravity 6. Crystallized chromium obtained by Fremy was unaffected by the strongest acids. Chromium forms three series of compounds : the chro- mous, typified by the chloride CrCL, in wbich chromium is a dyad ; the chromic or sesgwi -compounds, such as the oxide, Cr 2 O 3, and chromic chloride, Cr, 2 Cl 6, in which the metal plays the part of a tetrad, or pseudo-triad; and chromate compounds, in which it is a hexad, exemplified by the hexafluoride, CrF 6, the oxychloride, Cr0 2 Cl 2 , the anhy dride, Cr0 3, and potassium chromate, K 2 Cr0 4. In the hypothetical perchromic anhydride, Cr 2 O r, chromium may be regarded as an octad. Chromous salts resemble the ferrous, in forming a dark- brown compound when nitric oxide is added to their solutions. The anhydrous protoxide, CrO, has not been obtained ; and the hydrate 2CrO.H 2 O, precipitated of a brown colour from solutions by potassium hydrate, is a very unstable body. The dichloride CrCl 2 is a powerful deoxidizer ; it forms with water a blue solution, which turns green on exposure to the air. The salts of the sesquioxide, or chromic salts, have an acid reaction. They are green, or from red to violet in colour. Ammonia precipitates from solutions of the violet salts a grey-blue hydrate, and from solutions of the green salts, a grey-green hydrate, the former precipitate giving a red, the latter a green solution with acids. Potash or soda throws down from solutions of the violet or green salts a bluish-green hydrate, soluble in excess of the precipitant, but reprecipitated on boiling. Accord ing to Lowel there are four modifications of the hydrate of chrome, two green, one violet-carmine, and a violet- blue. The hydrate can be economically made by boiling two parts by weight of potassium chromate with one of sulphur ; the presence of a little potash assists the opera tion. Sesquioxide of chromium, Cr 3, occurs native in argillaceous deposits. It may be obtained in the amorphous state by the ignition of the hydrate, and crystallized by decomposing potassium chromate with chlorine at a red heat. It can be melted at a high temperature into a greenish-black mass, and is with difficulty reduced by charcoal at an intense heat. A mixture of nitric acid and potassium chlorate converts it into chromic acid. The chromites are a class of bodies in which chromic oxide Cr 2 3 is united with protoxides, as in the compound Cr 3 4, and in chrome ironstone, Cr 2 FeO 4. The latter, the most abundant ore of chromium, contains besides iron and chromium variableproportionsof magnesium and aluminium, and is isomorphous with magnetic iron ore, Fe 3 4, and spinel, MgAl 2 O 4. It is a massive and compact, granular, rarely crystallized, black-coloured mineral, of specific gravity about 4 4, and hardness 5 5. It occurs usually in serpentine, and is found in the Shetland Isles, the depart ment of Var in France, Volterra in Tuscany, Silesia, Bohemia, Roraas in Norway, the Urals, near Baltimore iu the United States, and in many other localities. In 1869 the exports of chrome ore from Norway amounted to 210 tons. Chrome ironstone can be decomposed in the dry way for analysis by fusion with potassium bisulphate, to which sodium carbonate and then a little nitre are subse quently added. Chromic chloride, Cr 2 Cl 6, can be obtained either in the anhydrous insoluble condition, or as the green hydrated salt, soluble in water. Similar compounds are the fluoride, Cr 2 F b, the bromide, Cr 2 Br 6 , and the iodide, Cr 2 I 6. The sesquisulphates of chromium are the anhydrous salt, Cr. 2 (S0 4 ) 3, the hydrated salts with 5 and 15 molecules of water, a basic sulphate, Cr 2 O 3 .2SO 3, and the chrome alums, of the general constitution Cr 2 M 2 (SO 4 ) 4, 24H 2 0, isomorphous with common alum. Certain oxides inter mediate between the sesquioxide and trioxide have been termed ckromates of chromium. The trioxide or anhydride of chromium, Cr0 3, com parable with sulphuric anhydride, S0 3, can be prepared by the action of strong sulphuric acid upon potassium bichromate ; as the liquid cools, the anhydride separates from it in crimson acicular crystals. It can also be obtained by decomposing barium chromate with nitric acid. Chromic anhydride deliquesces in air, and dissolves in water, forming a solution which contains chromic acid ; it is a powerful oxidizer, and acts violently on organic substances, such as alcohol and ether, becoming reduced to the sesquioxide. Dry ammonia gas is converted by it into nitrogen and aqueous vapour. &quot;When peroxide of hydrogen, H 9 O 2, is added to a solution of chromium trioxide, an unstable blue compound of probable constitution H 2 Cr 2 8 , or perchromic acid, is formed, which dissolves in ether, and is decomposed by potash and soda, but forms stable compounds with ammonia, quinine, and other bodies. Chromic acid, H 2 CrO 4, has not been isolated, and hydrated salts of the type HM Cr0 4 are unknown. The chromates are a large class of bodies, isomorphous with the sulphates. They are bitter and poisonous salts, mostly of a yellow or red colour, and except those of the alkali metals, and of calcium, strontium, and magnesium, are more or less insoluble in water. Most of the insoluble chromates are basic. The chromates of the alkali metals are the neutral or normal yellow salts, M 2 CrO 4, or M 2 O.CrO 3 , and the orange-red bichromates, or acid salts, M 2 0.2Cr0 3. Potas sium trichromate, K 2 0.3Cr0 3, represents a third series of chromates. With salts of lead, bismuth, and barium, the alkaline chromates give yellow precipitates ; with silver salts, a purplish red; and with mercurous salts, a brick-red precipitate. Boiled with hydrochloric acid they give a green solution of sesquichloride of chromium ; and with sulphurous acid, or with sulphuric acid and alcohol, sugar, and other reducing agents, they yield chrome alum. When a chromate is heated with sulphuric acid and common salt, vapours of oxychloride of chromium, or chlorochromic acid, 