BIVOUACK BLACK SEA. 



551 



as the petroleum, to protect iron from rusting, and 

 sometimes forms an ingredient in black sealing- 

 wax. 



Elastic bitumen yields easily to pressure, is flexible 

 and elastic. It emits a strong, bituminous odour, and 

 is about the weight of water. On exposure to the 

 air, it becomes hard, and loses its elasticity. It takes 

 up the traces of crayons in the same manner as the 

 caoutchouc, or Indian rubber, whence it has obtained 

 the name of the mineral caoutchouc. It lias hitherto 

 been found only in the lead mines of Derbyshire. 



Compact bitumen, or asphaltum, is of a shining 

 black colour, solid, and brittle, with a conchoidal 

 fracture. Its specific gravity is from 1 to 1'6. Like 

 the former varieties, it burns freely, and leaves but 

 little residue. It is found in Judea, in the Palatinate, 

 in France, in Switzerland, and in large deposits in 

 sandstone in Albania ; but no where so largely as in 

 the island of Trinidad, where it forms a lake three 

 miles in circumference, and of a thickness unknown. 

 A gentle heat renders it ductile, and, when mixed 

 with grease or common pitch, it is used for paying 

 the bottoms of ships, and is supposed to protect them 

 from the teredo of the West Indian seas. The an- 

 cients employed bitumen in the construction of their 

 buildings. The bricks of which the walls of Babylon 

 were built were, according to historians, cemented 

 with hot bitumen, which imparted to them great so- 

 lidity. 



BivouACK (from the German liwacht) ; the name 

 given to the modern system, by which the soldiers in 

 service lie in the open air, without tents, in opposi- 

 tion to the old system of camps and cantonments. 

 They remain dressed, in order to be ready, at a mo- 

 ment's warning, to take their places in order of 

 battle. Tents being laid aside, on the continent of 

 Europe, for the sake of diminishing the baggage of 

 an army, large masses of troops are always obliged 

 to bivouack, even if they are not near the enemy. 

 The soldier, however, is permitted to build himself a 

 hut of straw or branches, if circumstances allow it. 

 Frequent bivouacking is very injurious to the health, 

 and is also a great disadvantage to the countries in 

 which it takes place. 

 BLACK. See Colour. 



BLACK, Joseph, a distinguished chemist, born at 

 Bordeaux, of Scottish parents, in 1728, studied medi- 

 cine at Glasgow. Dr Cullen, his instructor, inspired 

 him with a taste for chemical studies. In 1754, he 

 was made doctor of medicine, at Edinburgh, and de- 

 livered an inaugural dissertation, De Humore acido a 

 ('ibis orto et Magnesia alba, which exhibits the out- 

 line of his discoveries relative to carbonic acid and 

 the alkalies. In 1756, he published his Experiments 

 on White Magnesia, Quicklime, and several other 

 Alkaline Substances, in the 2nd volume of the Essays, 

 Physical and Literary, of the Edinburgh Society. 

 He demonstrates the existence of an aerial fluid in 

 these substances, which he calls fixed air, the pre- 

 sence of which diminishes the corrosive power of the 

 alkalies and the calcarious earths. This discovery 

 may be considered as the basis of all those which have 

 immortalized the names of Cavendish, Priestley, La- 

 voisier, &c. , and given a new form to chemistry. In 

 1757, B. enriched this science with his doctrine of 

 latent heat, which has led to such important results. 

 In 1756, he was appointed professor of medicine and 

 lecturer on chemistry in the university at Glasgow, 

 in the place of Dr Cullen, and, In 1765, when Cullen 

 left the professor's chair in Edinburgh, he was there, 

 also, succeeded by B. No teacher inspired his dis- 

 ciples with such a zeal for study ; his lectures, there- 

 fore, contributed much to make the taste for chemical 

 science general in England. He died in 1799, at the 

 age of seventy-one. Upon Lovoisier's proposal, the 



academy of sciences, in Paris, had appointed him one 

 of its eight foreign members. His habits were 

 simple, his character cold and reserved. Though %>f 

 eminent ability as a chemist, he injured himself by 

 tiis long opposition to the reception of the new 

 chemical theory. At length, however, he was con- 

 vinced of its superior accuracy, and did justice to its 

 merits. There is a paper of his in the Philosophical 

 Transactions of 1774, and another in the Transactions 

 of the Royal Society of Edinburgh, in 1 791 . Two of 

 his letters on chemical subjects were published by 

 Crell and Lavoisier, and his Lectures on Chemistry, 

 in 1803, in 2 vols. by Robison. 



BLACK FOREST (in German, Schwarzwald) ; a 

 chain of mountains in the grand duchy of Baden and 

 the kingdom of Wurtemberg. It runs almost paral- 

 lel with the Rhine, from south to north, often only 

 from fifteen to twenty miles distant from this river ; 

 is about eighty-five miles long, and, from east to west, 

 in the southern part, about thirty miles wide ; in the 

 northern, about eighteen. The Danube rises in 

 these mountains, as well as many other rivers. 

 Those on the west side run into the Rhine, those on 

 the east side into the Danube. The Black Forest 

 is rather a chain of elevated plains, than of isolated 

 peaks. The highest summit, the Feldberg, measures 

 4610 German feet. Except from June to September, 

 these mountains are generally covered with snow, 

 and even during this period are not entirely free from 

 it. Among the many valleys of this chain, the 

 Murgthal is particularly celebrated for its beautiful 

 scenery. The whole chain consists of primitive 

 mountains : its skeleton, throughout, is granite ; its 

 higher points are covered with sand-stone, and other 

 layers of less consequence, and are surrounded by 

 heights composed of floetz rocks. On the western 

 side, at the foot, appears gneiss. Porphyry and clay- 

 slate are found on several heights, as likewise silver, 

 lead, copper, iron, cobalt, and mineral waters. The 

 woods are abundant, and consist mostly of pines and 

 similar species. The raising of cattle is the principal 

 branch of husbandry carriea on in this district The 

 ground is not fertile, and the inhabitants scattered 

 over the mountains, live extremely frugal, but are 

 very industrious. Their manner of living, building 

 their houses, and cultivating their lands, is very pe- 

 culiar. Till the seventeenth century, there was no 

 spirit of trade or industry among them ; but the wars 

 of that period developed it, and the manufactures of 

 glass, straw hats, wooden clocks, and other wooden 

 ware, are now very important. They make annually 

 more than 180,000 wooden clocks, the value of which 

 amounts to over half a million of guilders. Neustadt 

 and Furtwangen are the central points of this singu- 

 lar commerce, which embraces all Europe, and ex- 

 tends even to America. Large numbers of these 

 clocks are sent to Spain and Portugal, from whence 

 they go to South America. From the north of Ger- 

 many, and from Havre they are exported to the 

 United States. Of late, the clocks have been much 

 improved, and the correctness of some of them, made 

 of different woods, in order to counteract the influence 

 of the weather, is surprising. 



Two passes of the Black Forest became particu- 

 larly noted in the time of the French revolution the 

 Kniebis and the Holle passes. The former, at the 

 foot of the Murg, was taken in 1796 and 1797 ; the 

 latter is famous for Moreau's skilful retreat through 

 it in 1796. 



BLACK LEAD. See Plumbago. 



BLACK ROCK. See Buffalo. 



BLACK SKA ; with the ancients, known by the name 

 of Pontus Euxinus (q. v.) ; a sea which is situated 

 between Europe and Asia, bounded on the west by 

 Romania and Bulgaria, on the north by the Russian 



