BIT 
tiiat salt, therefore, affords the best test for 
discovering the bitter principle when no 
other substances are present, by which also 
it is decomposed. From recent experi- 
ments of Mr. Hatchett, it appears that the 
bitter principle is formed, along with tan, 
by the action of nitric acid on indigo. 
Bitter salt, native, in mineralogy, is of a 
greenish white, or smoke-grey colour. It oc- 
curs sometimes in earthy, sometimes in mass, 
and often in capillary crystals. When earthy 
it is without lustre, but when crystallised 
its lustre is between silky aud vitreous. It 
consists of sulphate of magnesia, more or 
less mixed with iron and allumina, and pro- 
bably some sulphat of allumina. It is found 
on the surface of decomposing argillaceous 
schistus, and sometimes of lime-stone. 
BITTERN. See Ardea. 
Bittern, in salt-works, the brine remain- 
ing after the salt is concreted : this they 
ladle off that the salt may be taken out of 
the pan, and afterwards put in again ; when 
being farther boiled it yields more salt. 
BITTERSPATH, in mineralogy, is grey- 
ish, or greenish white, passing into aspara- 
gus green. It occurs : i . disseminated or 
crystallised in rhomboids, or perfect or 
truncated at the solid angles ; 2 . short 
somewhat oblique, tetrahedral prisms, often 
bevelled at the edges; '3. compressed hex- 
aedrons. It is composed of 
Carbonate of lime 53 
magnesia 45 
Oxide of iron and manganese 3 
BIV 
100 
BITUMEN, in chemistry. The term 
bitumen has often been applied by chemists 
to all the inflammable substances that occur 
in the earth; but this use of the word is now 
so far limited, that sulphur and millite are 
most commonly excluded. It would be 
proper to exclude amber likewise, and to 
apply the term to those fossil bodies only 
which have a certain resemblance to oily 
and resinous substances. Bituminous sub- 
stances may be subdivided into two classes 
namely, bituminous oils, and bitumens, pro- 
perly so called. The first set possess nearly 
the properties of volatile oils, and ought in 
strict propriety, to be -classed with' these 
bodies; but as the chemical properties of 
bitumens have not yet been investigated 
with much precision, it is deemed rather 
premature to separate them from each other. 
Ihe second set possess properties peculiar 
to themselves. Only two species of bitu- 
minous oils have been hitherto examined 
by chemists. Others indeed have been 
mentioned ; but their existence has not been 
sufficiently authenticated. These twospecies 
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 properties : 
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 com- 
monly in ether, and in the fixed and vola- 
tile 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,’ dis- 
solves them, and converts them into a yel- 
low substance, soluble both in water and 
alcohol, and similar to the product formed 
by the action of nitrous acid on resins. The 
bitumens at present known may be reduced 
to three; namely, asphaltum, mineral tar 
and mineral caoutchouc. Bitumen has been 
found also united to a resinous compound 
in a curious substance first accurately exa- 
mined by Mr. Hatchett, to which he has 
given the name of retinasphaltum. United 
to charcoal in various proportions, it consti- 
tutes the numerous varieties of pit-coal, so 
much employed in this country as fuel. The 
asphaltum found in Albania is supposed to 
have constituted the chief ingredient of the 
Greek fire. Asphaltum is seldom absolutely 
pure ; for when alcohol is digested on it, tiie 
colour of the liquid becomes yellow, and by 
gentle evaporation a portion of petroleum 
is separated. Mineral tar seems to be no- 
thing else than asphaltum, 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 melt- 
ed pitch, not acted upon by alcohol, and 
which therefore appears to possess the oro- 
perties of asphaltum, with the exception of 
not being solid. By exposure to the air, it 
is said gradually to assume the state of as- 
phaltum. 
BIVALVES, one of the three general 
classes of shell-fish, comprehending all those. 
