Colchis was celebrated in Greek mythology as the destination of the Argonauts, the home of Medea and the special domain of sorcery. Several Greek colonies were founded there by Miletus. At a remote period it seems to have been incorporated with the Persian empire, though the inhabitants evidently enjoyed a considerable degree of independence; in this condition it was found by Alexander the Great, when he invaded Persia. From this time till the era of the Mithradatic wars nothing is known of its history. At the time of the Roman invasion it seems to have paid a nominal homage to Mithradates the Great and to have been ruled over by Machares, his second son. On the defeat of Mithradates by Pompey, it became a Roman province. After the death of Pompey, Pharnaces, the son of Mithradates, rose in rebellion against the Roman yoke, subdued Colchis and Armenia, and made head, though but for a short time, against the Roman arms. After this Colchis was incorporated with Pontus, and the Colchians are not again alluded to in ancient history till the 6th century, when, along with the Abasci or Abasgi, under their king Gobazes, whose mother was a Roman, they called in the aid of Chosroes I. of Persia (541). The importance of the district, then generally called Lazica from the Lazi (cf. mod. Lazistan) who led the revolt, was due to the fact that it was the only remaining bar which held the Persians, already masters of Iberia, from the Black Sea. It had therefore been specially garrisoned by Justinian under first Peter, a Persian slave, and subsequently Johannes Tzibos, who built Petra on the coast as the Roman Headquarters. Tzibos took advantage of the extreme poverty of the Lazi to create a Roman monopoly by which he became a middleman for all the trade both export and import. Chosroes at once accepted the invitation of Gobazes and succeeded in capturing Petra (A.D. 541). The missionary zeal of the Zoroastrian priests soon caused discontent among the Christian inhabitants of Colchis, and Gobazes, perceiving that Chosroes intended to Persianize the district, appealed to Rome, with the result that in 549 one Dagisthaeus was sent out with 7000 Romans and 1000 auxiliaries of the Tzani (Zani, Sanni). The “Lazic War” lasted till 556 with varying success. Petra was recaptured in 551 and Archaeopolis was held by the Romans against the Persian general Mermeroes. Gobazes was assassinated in 552, but the Persian general Nachoragan was heavily defeated at Phasis in 553.
By the peace of 562 the district was left in Roman possession, but during the next 150 years it is improbable that the Romans exercised much authority over it. In 697 we hear of a revolt against Rome led by Sergius the Patrician, who allied himself with the Arabs. Justinian II. in his second period of rule sent Leo the Isaurian, afterwards emperor, to induce the Alans to attack the Abasgi. The Alans, having gained knowledge of the district by a trick, invaded Lazica, and, probably in 712, a Roman and Armenian army laid siege to Archaeopolis. On the approach of a Saracen force they retired, but a small plundering detachment was cut off. Ultimately Leo joined this band and aided by the Apsilian chief Marinus escaped with them to the coast.
From the beginning of the 14th to the end of the 17th century the district under the name Mingrelia (q.v.) was governed by an independent dynasty, the Dadians, which was succeeded by a semi-independent dynasty, the Chikovans, who by 1838 had submitted to Russia, though they retained a nominal sovereignty. In 1866 the district was finally annexed by Russia.
For the kings see Stokvis, Manuel d’histoire, i. 83.
(J. M. M.)
COLCOTHAR (adapted in Romanic languages from Arabic golgotar, which was probably a corruption of the Gr. χάλκανθος, from χαλκός, copper, ἄνθος, flower, i.e. copper sulphate), a name given to the brownish-red ferric oxide formed in the preparation of fuming sulphuric (Nordhausen) acid by distilling ferrous sulphate. It is used as a polishing powder, forming the rouge of jewellers, and as the pigment Indian red. It is also known as Crocus Martis.
COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kälte, kalt, Dutch koude, koud), subjectively the sensation which is excited by contact with a substance whose temperature is lower than the normal; objectively a quality or condition of material bodies which gives rise to that sensation. Whether cold, in the objective sense, was to be regarded as a positive quality or merely as absence of heat was long a debated question. Thus Robert Boyle, who does not commit himself definitely to either view, says, in his New Experiments and Observations touching Cold, that “the dispute which is the primum frigidum is very well known among naturalists, some contending for the earth, others for water, others for the air, and some of the moderns for nitre, but all seeming to agree that there is some body or other that is of its own nature supremely cold and by participation of which all other bodies obtain that quality.” But with the general acceptance of the dynamical theory of heat, cold naturally came to be regarded as a negative condition, depending on decrease in the amount of the molecular vibration that constitutes heat.
The question whether there is a limit to the degree of cold possible, and, if so, where the zero must be placed, was first attacked by the French physicist, G. Amontons, in 1702-1703, in connexion with his improvements in the air-thermometer. In his instrument temperatures were indicated by the height at which a column of mercury was sustained by a certain mass of air, the volume or “spring” of which of course varied with the heat to which it was exposed. Amontons therefore argued that the zero of his thermometer would be that temperature at which the spring of the air in it was reduced to nothing. On the scale he used the boiling-point of water was marked at 73 and the melting-point of ice at 51½, so that the zero of his scale was equivalent to about -240° on the centigrade scale. This remarkably close approximation to the modern value of -273° for the zero of the air-thermometer was further improved on by J. H. Lambert (Pyrometrie, 1779), who gave the value -270° and observed that this temperature might be regarded as absolute cold. Values of this order for the absolute zero were not, however, universally accepted about this period. Laplace and Lavoisier, for instance, in their treatise on heat (1780), arrived at values ranging from 1500° to 3000° below the freezing-point of water, and thought that in any case it must be at least 600° below, while John Dalton in his Chemical Philosophy gave ten calculations of this value, and finally adopted -3000° C. as the natural zero of temperature. After J. P. Joule had determined the mechanical equivalent of heat, Lord Kelvin approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature which was independent of the properties of any particular substance and was based solely on the fundamental laws of thermodynamics (see [Heat] and [Thermodynamics]). It followed from the principles on which this scale was constructed that its zero was placed at -273°, at almost precisely the same point as the zero of the air-thermometer.