TETRAZINES  , in organic

chemistry, a group of compounds containing the ring system C•N•N CNN C•N•C C•NN,Or &.Nt, Or &.N.&; only derivatives of the first two types are known . The members of the first series may be prepared by oxidizing osazones (i.e. dihydrazones of a-diketones), dihydrotetrazines resulting . Dihydro-derivatives of the second type are formed from hydrazine and imino-ethers (A . Pinner, Ber., 1893, 26, p . 2126; 1894, 27, p . 984); these easily oxidize to the corresponding tetrazines, which are stable towards acids; their dihydro-derivatives, however, are decomposed, the group—NH.NH—being eliminated as hydrazine and replaced by oxygen, with consequent formation of the five membered oxybiazole ring . Concentrated acids convert the dihydro-tetrazines into isodihydrotetrazines, thus:-- R•C•NH•NH R•C N?i'•N N•N :C•R N•NH•C•R, the N-alkyl derivatives of which type may be prepared by the action of alcoholic potash and chloroform on aromatic hydrazines . Much discussion has circulated about the decomposition of diazo-acetic ester, from which A . Hantzsch and 0 . Silberrad (Ber., 1900, 33, p . 58) obtained what they considered to be a dihydrotetrazine, thus: CH•CO2R H02C•CH•N:N HC•NH•N N:N •CH•CO2H N•NH•CH . which it is connected by a chain bridge (1855) and two railway bridges .

The handsome

chateau of the counts of Thun (built in 1667–73 and restored in 1788), which occupies a rocky height above the town, was at one time fortified, and was a place of some importance during the Seven Years' War . It contains a magnificent library, with many valuable MSS. and fne collections of coins and armour . In addition to being the principal emporium for the Austrian traffic on the Elbe, Tetschen has a considerable industry, its products comprising chemicals, oil, soap, cotton stuffs, plaster of Paris, glazed and coloured paper, cellulose, beer, flour and preserved fish . The town of Tetschen originally lay on the south side of the castle rock, but after its destruction by a flood, it was moved in 1059 to its present site . In 1305 it came into the hands of the knights of Wartenberg, who held it for two hundred years . In 1534 the Saxon lords of Biinau obtained it and introduced the Protestant religion, which was exterminated when, after the battle of the White Hill (1620) the Bunau family was driven out . The lordship was bought from them in 1628 by the Freiherr von Thun, by whose descendants, the Counts Than, it is still held .