BLA 
BLA 
the shells of which are composed of two 
pieces, joined together by a hinge. 
The Linnaean genera of bivalve shells are 
the following fourteen : 
Anomia Mya 
Area Mytillus 
Astraea Solen 
Cardium Spondylus 
Chama Tellina 
Donax Tillus 
Mactra Venus. 
BIXA, in botany, a genus of Polyandria 
Monogynia class and order. Natural order 
of Columniferae ; Tiliacae, Jussieu. Essential 
character : corolla ten petalled ; calyx five- 
toothed ; capsule hispid, bivalve. B. aenel- 
lana is a shrub with an upright stem, eight 
or ten feet high, sending out many branches 
at the top, forming a regular head ; these 
are garnished with heart-shaped leaves end- 
ing 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 native 
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, arid 
therefore exhibits no colour. Bodies of a 
black colour are found more inflammable, 
because the rays of light falling on them 
are not reflected outwards, but enter the 
body and are often reflected and refracted 
within it, till they are stifled and lost. They 
are also found lighter, cceteris paribus, 
than white bodies, being more porous. It 
may be added, that clothes dyed of this 
colour wear out faster than those of any 
other, because their substance is more 
penetrated and corroded by the vitriol ne- 
cessary to strike their dye, than other bo- 
dies are by the galls and alum which suffice 
for them. The inflammability of black 
bodies, and their disposition to acquire 
heat, beyond those of other colours, are 
easily evinced. Some appeal to the experi- 
ment of a white and black glove worn in the 
same sun ; the consequence will be, a very 
sensibly greater degree of heat in the one 
hand than the other. Others allege the 
phenomena 'of burning-glasses, by which 
black bodies are always found to kindle 
soonest : thus, a burning-glass, too weak to 
have any visible effect at all upon white 
paper, will readily kindle the same paper 
rubbed over with ink. 
Dr. Watson, the present Bishop of Lan- 
daff, covered the bulb of a thermometer 
with a black coating of India ink, in con- 
sequence of which the mercury rose ten 
degrees. Phil. Trans, vol. lxiii. Black 
clothes heat more, and dry sooner in the 
sun than white clothes. Black is therefore 
a bad colour for clothes in hot climates ; 
but a fit colour for the linings of ladies’ 
summer hats. 
Black act, in law, so called from the 
devastations committed in Hampshire by 
persons in disguise, or with their faces 
blacked; to prevent which, it is enacted 
by 31 George II. c. 42, that persons hunt- 
ing, armed, and disguised, and killing or 
stealing deer, or robbing warrens, &c. or 
setting fire to any house, barn, or wood, or 
shooting at any person, or sending anony- 
mous letters, or letters signed with a ficti- 
tious name, demanding money, &c. or 
rescuing such offenders ; are guilty of felony 
without benefit of clergy. 
Black, bone, is made with the bones of 
oxen, cows, &c. and is used in painting ; 
but is not so much esteemed as ivory- black. 
Black, currier’s, a black made with gall- 
nuts, sour beer, and old iron, termed the 
first black. The second black, which gives 
the gloss of the leather, is composed of gall- 
nuts, copperas, and gum arabic. 
Black, earth, a sort of coals found in the 
ground, which the painters and limners use 
to paint in fresco, after it has been w'ell 
ground. 
There is also a black made with gall-nuts, 
copperas, or vitriol, such as common ink. 
And a black made with silver and lead, 
which serves to fill up the cavities of en- 
graved things. 
Black, ivory, otherwise called velvet- 
black, is burnt ivory, which becoming quite 
black, and being reduced to thin plates, is 
ground in water, and made into troches, to 
be used by painters, and by jewellers, who 
set precious stones to blacken the ground 
of the collets, and give the diamonds a feint 
or foil. In order to be good, it ought to 
be tender, friable, and thoroughly ground. 
Black, lamp, the sooty smoke of rosin. 
There is some in powder and some in lumps, 
and is mostly brought from Sweden and 
Norway. It is used on various occasions, 
particularly for making the printers’ ink, 
for which purpose it is mixed with oil of 
walnuts, or linseed, and turpentine, all 
boiled together. 
Black lead has long been known under 
the name of plumbago, it is however pro- 
perly denominated in the modern chemistry 
according to its component parts, a cat- 
