Chronographer

[Gr. chronos, and graphein, to write.] One who writes concerning time, or the events of, time; a chronologist. Chronography, n. The description of time past. Chronologer, Chronologist, n. [See CHRONOLOGY.] One who studies or is versed in chronology; one who attempts to discover the true dates of past events and transactions, and to arrange them under their proper years. Chronologic, Chronological, a . Relating to chronology; according to the order of time; as, in chron ological succe ion. Chronologʻically, adv . In a chronological manner. Chronology, n. [Fr. chronos , and logos , doctrine.) The doctrine or science of time, or of computing dates: the method of ascertaining the true periods, or years, when past events took place, and arranging them in their proper order, according to their dates. drated intermediate oxide. The protoxide of chromium Chronogram'matist, n. A writer of chronograms. forms a double sulphate with sulphate of potash, closely corresponding to the double sulphate of iron and potash in form and composition. The crystals are of a fine blue color. Sesquioxide of chromium is easily obtained as a grayish-green hydrate, by boiling with alcohol a solution of bichromate of potash acidulated with sulphuric acid. The alcohol seizes half the oxygen of the chromic acid, leaving the sesquioxide free to form a sulphate with the sulphuric acid. On the addition of ammonia, a bulky, gelatinous, grayish-green precipitate of hydrated sesquioxide is produced, which, when dry, contains ten equivalents of water. In the hydrated condition it is readily soluble in acids, forming salts which do not crystallize. These salts, like the oxide, exist under several conditions, each condition giving rise to di imilar properties. As this subject is rather complicated, the reader is referred to the article IsoMERISM, where the subject is fully treated. The anhydrous green oxide is not decomposed by heat; hence it is of great use in china and enamel-painting. It is generally prepared for this purpose by exposing chromate of mercury to a red heat. The difficulty with which this oxide is decomposed by ordinary chemical reagents has rendered it useful as a pigment for printing bankers' cheques and other important documents; but a great objection to its use is the fact of its being so hard that the pens used for writing upon drafts printed by it are speedily worn out. Oxide of chromium is the coloring-matter of the emerald, pyrope, greenstone, and other minerals. Chromic acid has already been considered, under that head. - Per chromic acid is formed by adding an aqueous solution of peroxide of hydrogen to chromic acid. The liquid a umes a deep-blue color, but is rapidly decomposed with evolutions of oxygen. If, however, the solution is agitated with ether, the per chromic acid is isolated without decomposition, and may be made to form pretty stable salts with ammonia and certain organic bases. Strong acids decompose these salts, setting free the blue per chromic acid. Chlorides of C. There are two principal chlorides of chromium, the pro to chloride, CrCl, and the sesquichloride, CrCl3. The former is formed by pa ing a dry current of hydrogen over the sesquichloride heated to redne ; hydrochloric acid is given off, and the pro to chloride remains in the form of a white powder, soluble in water, with which it forms a bluish-green solution that rapidly absorbs oxygen from the air. - Sesquichlo ride of chromium is formed in beautiful transparent plates of the color of peach-blo oms by pa ing a current of dry chlorine over a mixture of sesquioxide of chromium mixed with charcoal contained in a porcelain tube heated to redne . Being volatile, the sesquichloride condenses at the cool end of the tube in the beautiful form just described. Thus prepared, it is quite insoluble in water and acids. Solution of sesquichloride of chromium is prepared from the hydrated sesquioxide by di olving it in hydrochloric acid. The solution, on evaporation, yields green crystals, containing two equivalents of hydrochloric acid and ten equivalents of water. It is a singular fact that only two-thirds of the chlorine contained in the solution of this salt is precipitated by nitrate of silver.