Page:The American Cyclopædia (1879) Volume IV.djvu/783

 COBALT OOBB 767 fers a remarkably delicate test for the presence of cobalt in solutions. This yellow has been used sparingly, on account of its cost, in aqua- relle and oil painting. By precipitating cobalt with phosphate of soda, we have a red-violet color, the shade of which varies according to the temperature at which it is prepared. A fine cobalt brown is produced by calcining a mixture of sulphate of cobalt, ammonia, and iron. Some of the salts of cobalt are red when they contain water, and blue when they are anhydrous. This property is made use of in what is called sympathetic ink. If we write with a dilute solution of chloride of cobalt on paper, and allow the tracings to dry at ordi- nary temperatures, the letters will be scarcely visible. Upon the application of heat the wri- ting becomes visible, with a blue color, or sometimes green if nickel be present; the color again disappears on the absorption of moisture. A fine green color is produced by precipitating cobalt from its solutions, by means of a mixture of prussic acid and pot- ash ; but the cost of production must prevent any extensive application of this color. Since the discovery of photography, the use of cobalt- blue glass has greatly increased. It is an in- teresting fact in optics that blue glass permits all the chemical rays of light to pass freely through it, while the yellow are intercepted. Pieces of blue glass are used to eliminate the yellow rays when the colors of flames are to be examined for the violet hue of potash, and in other cases of optical research. The oxide of cobalt, prepared by precipitating the chloride with potassa, has been employed in rheu- matism ; it is emetic in doses of 10 to 20 grains. The salts of cobalt are irritant poi- sons. The employment of metallic cobalt in the manufacture of German silver would make that article too expensive for general use ; but in small quantities it enters into alloys, in as- sociation with nickel, as an incidental compo- nent. The deposition of metallic cobalt by the battery can be accomplished the same as is now so extensively done with nickel, and this method is sometimes employed to procure small quantities of the metal. Some of the salts of cobalt are of great value to the chem- ist in his laboratory, as affording delicate tests for the presence of other bodies. One of the methods for the manufacture of oxygen from bleaching powders is founded upon the some- what obscure formation and subsequent de- composition of cobaltic acid. A very small quantity of a solution of cobalt suffices to evolve all of the oxygen from a given quantity of chloride of lime. The ammoniacal com- pounds of cobalt were prepared and fully studied by Genth and Gibbs. The nitrate of cobalt is sometimes employed as a reagent for the blowpipe. The compounds of cobalt are easily recognized by the intense blue color which they communicate to a bead of borax in the oxidating flame. Zaffre or safflor is a mix- ture of roasted ore and quartz, used in pottery. 203 VOL. iv. 49 COBAIV, a city of Guatemala, capital of the department of Vera Paz, on the left bank of the Rio Dulce, near its source, in lat. 15 30' N"., Ion. 90 30' W., 55 m. N. of the city of Guatemala; pop. about 15,000. It is situated in a remarkably fertile valley, covered with thriving plantations of sugar cane, bananas, and pimento and fruit trees. The inhabitants, chiefly Indians, are industrious and wealthy. COBB, a N. W. county of Georgia, bounded S. E. by the Chattahoochee, and drained by several creeks; area, 529 sq. m. ; pop. in 1870, 13,814, of whom 3,217 were colored. The sur- face is hilly, and in part mountainous. The soil is fertile. The rocks are granitic and meta- morphic, and produce gold. The Western and Atlantic railroad intersects the county. The chief productions in 1870 were 58,296 bush- els of wheat, 215,522 of Indian corn, 23,182 of oats, 130,650 Ibs. of butter, and 1,972 bales of cotton. There were 893 horses, 799 mules and asses, 1,784 milch cows, 3,035 other cattle, 2,843 sheep, and 10,897 swine; 2 manufacto- ries of cotton, 1 of woollen goods, 1 of paper, 2 wool-carding and 3 leather-currying estab- lishments, 1 flour mill, 4 saw mills, and 4 tan- neries. Capital, Marietta. COBB, Howell, an American politician, born at Cherry Hill, Ga., Sept. 7, 1815, died in New York, Oct. 9, 1868. He graduated at Franklin college in 1834, and was admitted to the bar in 1836. In 1837 he was elected by the legisla- ture solicitor general of the western circuit. He began his congressional career in 1843, hav- ing been elected to the house of representa- tives, in which by three successive reelections he sat till 1851. He was distinguished for his familiarity with the rules of the house, his skill as a debater, his strong professions of attach- ment to the Union, and his equally earnest ad- vocacy of state rights. He became the leader of the southern party in the house, and upon the assembling of the 31st congress in Decem- ber, 1849, he was elected speaker after a vio- lent contest. He demanded the extension of slavery into California and New Mexico by federal authority, and supported the compro- mise measures of 1850. In 1851 he was elected governor of Georgia, defeating the candidate of the extreme southern rights party, which opposed the compromise. At the expiration of his term in 1853 he resumed the practice of the law, but in 1855 was again elected to con- gress, and in 1856 made a tour through the north to support the election of Mr. Bu- chanan. In March, 1857, he became secre- tary of the treasury in President Buchanan's cabinet, and held that office till Dec. 10, 1860, when he resigned to engage in the secession movement. In February, 1861, he became president of the confederate congress assem- bled at Montgomery, Ala., and afterward trans- ferred to Richmond, but retired Feb. 18, 1862, on account of misunderstandings with Jeffer- son Davis. Subsequently he was commissioned a major general, but took little part in military