Two oxides of iridium are known, namely the sesquioxide, Ir203, and the dioxide, Ir02, corresponding to which there are two series of salts, the sesqui-salts and the iridic salts; a third series of salts is also known (the iridious salts) derived from an oxide IrO.
Iridium sesquioxide, Ir 2 0 3, is obtained when potassium iridium chloride is heated with sodium or potassium carbonates, in a stream of carbon dioxide.
Three characteristic oxides of cobalt are known, the monoxide, CoO, the sesquioxide, C0203, and tricobalt tetroxide, C0304; besides these there are probably oxides of composition Co02, Co 8 0 9, C0607 and C0405.
Cobalt sesquioxide, Co 2 0 3, remains as a dark-brown powder when cobalt nitrate is gently heated.
The ore generally occurs in the form of oxides, manganite and pyrolusite, and contains a high percentage of sesquioxide of manganese.
Molybdenum combines with oxygen to form many oxides, the most important of which are: the monoxide, MoO.n (H 2 O), the sesquioxide, M0203, the dioxide, MoO 2, and the trioxide, MoO 3.
Molybdenum sesquioxide, Mo 2 O 3, a black mass insoluble in acids, is formed by heating the corresponding hydroxide in vacuo, or by digesting the trioxide with zinc and hydrochloric acid.
Four oxides of sulphur a.re known, namely sulphur dioxide, S02, sulphur trioxide, S03, sulphur sesquioxide, S203, and persulphuric anhydride, S 2 0 7.
Sulphur sesquioxide, S203, is formed by adding well-dried flowers of sulphur to melted sulphur trioxide at about 12-15° C. The sulphur dissolves in the form of blue drops which sink in the liquid and finally solidify in blue-green crystalline crusts.
Although this acid appears to be derived from an oxide S203, it is not certain that the known sesquioxide is its anhydride.
Fusion with caustic potash converts it into a mixture of potassium ruthenate and ruthenium sesquioxide, Ru 2 0 3, which is a black, almost insoluble powder.
It is also obtained by passing chlorine into a suspension of lead oxide or carbonate, or of magnesia and lead sulphate, in water; or by treating the sesquioxide or red oxide with nitric acid.
Lead sesquioxide, Pb203, is obtained as a reddish-yellow amorphous powder by carefully adding sodium hypochlorite to a cold potash solution of lead oxide, or by adding very dilute ammonia to a solution of red lead in acetic acid.
Bismuth and antimony give (the latter very readily) sesquioxide (Bi 2 O 3 and Sb203, the latter being capable of passing into Sb204).
Titanium sesquioxide, Ti 2 O 3, is formed by heating the dioxide in hydrogen.
The sesquioxide, Os203, results on heating osmium with an excess of the tetroxide.
The sesquioxide, Pr203, is obtained as a greenish white mass by the reduction of the peroxide.
Wohler reduced the sesquioxide by zinc, and obtained a shining green powder of specific gravity 6.81, which tarnished in air and dissolved in hydrochloric acid and warm dilute sulphuric acid, but was unacted upon by concentrated nitric acid.
Moissan (Comptes rendus, 1893, 116, p. 349; 1894, 119, p. 185) reduces the sesquioxide with carbon, in an electric furnace; the product so obtained (which contains carbon) is then strongly heated with lime, whereby most of the carbon is removed as calcium carbide, and the remainder by heating the purified product in a crucible lined with the double oxide of calcium and chromium.
Goldschmidt (Annalen, 1898, 301, p. 19) in which the oxide is reduced by metallic aluminium; and if care is taken to have excess of the sesquioxide of chromium present, the metal is obtained quite free from aluminium.
Chromium forms three series of compounds, namely the chromous salts corresponding to CrO, chromous oxide, chromic salts, corresponding to Cr203, chromium sesquioxide, and the chromates corresponding to Cr0,, chromium trioxide or chromic anhydride.
Chromium sesquioxide is a basic oxide, although like alumina it acts as an acid-forming oxide towards strong bases, forming salts called chromites.
Various other oxides of chromium, intermediate in composition between the sesquioxide and trioxide, have been described, namely chromium dioxide, Cr203 Cr03, and the oxide Cr03.2Cr203.
The sesquioxide, Cr 2 0 3, occurs native, and can be artificially obtained in several different ways, e.g., by igniting the corresponding hydroxide, or chromium trioxide, or ammonium bichromate, or by passing the vapours of chromium oxychloride through a red-hot tube, or by ignition of mercurous chromate.
Several forms of hydrated chromium sesquioxide are known; thus on precipitation of a chromic salt, free from alkali, by ammonia, a light blue precipitate is formed, which after drying over sulphuric acid, has the composition Cr 2 0 3 -7H 2 0, and this after being heated to zoo° C. in a current of hydrogen leaves a residue of composition CrO.
It is readily soluble in water, melts at 193° C., and is decomposed at a higher temperature into chromium sesquioxide and oxygen; it is a very powerful oxidizing agent, acting violently on alcohol, converting it into acetaldehyde, and in glacial acetic acid solution converting naphthalene and anthracene into the corresponding quinones.
Gaseous ammonia passed over the oxide reduces it to the sesquioxide with formation of nitrogen and water.
Thechromites maybe looked upon as salts of chromium sesquioxide with other basic oxides, the most important being chromite (q.v.).
Chromic chloride, CrC1 31 is obtained in the anhydrous form by igniting a mixture of the sesquioxide and carbon in a current of dry chlorine; it forms violet laminae almost insoluble in water, but dissolves rapidly in presence of a trace of chromous chloride; this action has been regarded as a catalytic action, it being assumed that the insoluble chromic chloride is first reduced by the chromous chloride to the chromous condition and the original chromous chloride converted into soluble chromic chloride, the newly formed chromous chloride then reacting with the insoluble chromic chloride.
Yet, unlike potassium or lead, it forms a feebly basic sesquioxide similar to manganic oxide, Mn203.
(See Iron And Steel.) Compounds Manganese forms several oxides, the most important of which are manganous oxide, MnO, trimanganese tetroxide, Mn304, manganese sesquioxide, Mn203, manganese dioxide, Mn02, manganese trioxide, Mn03, and manganese heptoxide, Mn207.
Manganese sesquioxide, Mn203, found native as the mineral braunite, may be obtained by igniting the other oxides in a mixture of nitrogen and oxygen, containing not more than .26% of the latter gas (W.
In the absence of air the reaction proceeds slightly differently, some manganese sesquioxide being formed; 3MnO 2 +2KHO = K 2 Mn0 4 +Mn 2 0 3 +H 2 O.
The sesquioxide, Ce 2 O 3, is obtained by heating the carbonate in a current of hydrogen.
Nickel sesquioxide, N1203, is formed when the nitrate is decomposed by heat at the lowest possible temperature, by a similar decomposition of the chlorate, or by fusing the chloride with potassium chlorate.
Baubigny, Comptes rendus, 1878, 87, p. 1082), or by heating the sesquioxide in hydrogen at 190° C. (H.
The sesquioxide, Ag 4 O 3, is supposed to be formed when silver peroxide is treated with ammonia (Watson, Jour.