BIT 



BLA 



bitumen has. often been applied by che- 

 mists to all the inflammable substances 

 that occur in the earth ; but this use of 

 the word is now so far limited, that sul- 

 phur and millite are most commonly ex- 

 cluded. It would be proper to exclude 

 amber likewise, and to apply the term to 

 those fossil bodies only which have a cer- 

 tain resemblance to oily and resinous 

 substances. Bituminous substances may 

 be subdivided into two classes, namely, 

 bituminous oils, and bitumens, properly 

 so called. The first set possesses nearly 

 the properties of volatile oils, and ought, 

 in strict propriety, to be classed with 

 these bodies; but as the chemical pro- 

 perties of bitumens have not yet been in- 

 vestigated with much precision, it is 

 deemed rather premature to separate 

 them from each other. The second set 

 possess properties peculiar to themselves. 

 Only two species of bituminous oils have 

 been hitherto examined by chemists. 

 Others indeed have been mentioned; but 

 their existence has not been sufficiently 

 authenticated. These two species are 

 called petroleum, and maltha, or sea- 

 wax ; the first is liquid, the second solid. 

 See PETROLEUM and MALTHA. 



The true bituminous substances may 

 be distinguished by the following 1 proper- 

 ties : They are either solid, or of the 

 consistence of tar : their colour is usually 

 brown or black : they have a peculiar 

 smell, or at least acquire it when rubbed ; 

 this smell is known by the name of the 

 bituminous odour ; they become electric 

 by friction, though not insulated; they 

 melt when heated, and burn with a strong- 

 smell, a bright flame, and much smoke : 

 they are insoluble in water and alcohol, 

 but dissolve most commonly in ether, 

 and in the fixed and volatile oils ; they do 

 not dissolve in alkaline leys, nor form 

 soap ; acids have little action on them ; 

 the sulphuric scarcely any ; the nitric, by 

 long and repeated digestion, dissolves 

 them, and converts them into a yellow 

 substance, soluble both in water and alco- 

 hol, and similar to the product formed by 

 the action of nitrous acid on resins. The 

 bitumens at present known may be re- 

 duced to three ; namely, asphaltum, mi- 

 neral tar, and mineral caoutchouc. Bitu- 

 men has been found also united to a re- 

 sinous compound, in a curious substance 

 first accurately examined by Mr. Hatch- 

 ett, to which he has given the name of 

 retinasphaltum. United to charcoal in 

 various proportions, it constitutes the nu- 

 merous varieties of pit-coal, so much em- 

 ployed in this country as fuel. The as- 

 phaltum found in Albania is supposed to 



have constituted the chief ingredient of 

 the Greek fire. Asphaltum is seldom ab- 

 solutely pure ; for when alcohol is digest- 

 ed on it, the colour of the liquid becomes 

 yellow, and by gentle evaporation a por- 

 tion of petroleum is separated. Mineral 

 tar seems to be nothing else than asphal- 

 tum containing a still greater proportion 

 of petroleum. When alcohol is digested 

 on it, a considerable quantity of that oil 

 is taken up ; but there remains a black 

 fluid substance like melted pitch, not 

 acted upon by alcohol, and which there- 

 fore appears to possess the properties of 

 asphaltum, with the exception of not be- 

 ing solid. By exposure to the air, it is 

 said gradually to assume the state of as- 

 phaltum. 



BIVALVES, one of the three general 

 classes in Conchology, comprehending all 

 those, the shells of which are composed 

 of two pieces joined together by a hinge. 



The Linnxan genera of bivalve shells 

 are the following fourteen : 



Anomia Mytillus 



Area Ostrea 



Cardium Pinna 



Chama Solen 



Donax Spondylus 



Mactra Tellina 



My a Venus. 



BIXA, in botany, a genus of Polyandria 

 Monogynia class and order. Natural or- 

 der of Columniferee : Tiliacx, Jussieu. ' 

 Essential character : corolla ten petalled ; 

 calyx five-toothed ; capsule hispid, bi- 

 valve. B. amellana is a shrub with an up- 

 right stem, eight or ten feet high, send- 

 ing out many branches at th*e top, form- 

 ing a regular head ; these are garnished 

 with heart-shaped leaves, ending in a 

 point ; the flowers are produced in loose 

 panicles, at the end of the branches, of a 

 pale peach colour, having large petals. 

 There is but one species, which is a na- 

 tive both of the East and West Indies. 



BLACK, something opake and porous, 

 that imbibes the greatest part of the light 

 that falls on it, reflects little or none, and 

 therefore exhibits no colour. Bodies of 

 a black colour are found more inflamma- 

 ble, because the rays of light falling on 

 them are not reflected outwards, but en- 

 ter the body, and are often reflected and 

 refracted within it, till they are stifled 

 and lost. They are also found lighter, 

 cueteris paribus, than white bodies, being 

 more porous. It may be added, that 

 clothes dyed of this colour wear out fast- 

 er than those of any other, because their 

 substance is more penetrated and cor- 

 roded by the vitriol necessary to strike 



