V E B 
!0U 
P E A 
°f thin membrane and carbonat of lime. 
Their iridescence is obviously the conse- 
quence of the lamellated structure. 
Nir. Hatchett found that what is called the 
bone of the cuttle-fish is exactly similar to 
mother-of-pearl shells in its composition. 
From the comparative analysis of shells 
and bones Mr. Hatchett was induced to com- 
pare them together, and has shewn that por- 
celanous shells bear a striking resemblance to 
enamel of teeth, while mother-of-pearl shells 
bear the same resemblance to the substance 
of teeth or bone: with this difference, that 
in enamel and bone the earthy salt is phos- 
phat of lime, whereas in shells it is pure car- 
bonat of lime. 
PEARLS, artificial. Attempts have been 
made to take out stains from pearls, and to 
render the foul opaque-coloured ones equal 
in lustre to the Oriental. Abundance of pro- 
cesses are given for this purpose in books of 
secrets and travels ; but they are very far 
from answering what is expected from them. 
Pearls may be cleaned indeed from any ex- I 
ternal foulnesses by washing and rubbing j 
them with a little Venice soap and warm wa- ; 
ter, or with ground rice and salt, with starch ! 
and powder-blue, plaister of Paris, coral, 
white vitriol and tartar, cuttle-bone, pumice- : 
stone, and other similar substances; but a 
Stain that reaches deep into the substance of 
pearls is impossible to be taken out. Nor | 
can a number of small pearls be united into 
a mass similar to an entire natural one, as 
some pretend. j 
d here are, however, methods of making 
artificial pearls, in such a manner as to be 
with difficulty distinguished from the best 
Oriental. The ingredient used for this pur- i 
pose was long kept a secret ; but it is now 
discovered to be a fine silver-like substance 
found upon the under side of the scales of! 
the blay or bleak. The scales, taken off in 
the usual manner, are washed and rubbed 
with fresh parcels of fair water, and the se- 
veral liquors suffered to settle: the water be- 
ing then poured off, the pearly matter re- j 
mains at the bottom, of the consistence of : 
oil, called by the French essence <f orient. A 
little of this is dropped into a hollow bead of 
blueish glass, and sunken about so as to line j 
the internal surface ; after which the cavity ’ 
is filled up with wax, to give solidity and 
weight. Pearls made in this manner are dis- 
tinguishable from the natural only by their 
having fewer blemishes, 
PEA T, a well-known inflammable sub- 
stance, used in many parts of the world as 
fuel. There are two species. 
It consists, according to Kirwan, of 
clay mixed with calcareous earths and py- 
rites ; sometimes also it contains common 
salt. YV hile soft it is formed into oblong 
pieces for fuel, after the pyritaceous and 
stony matters are separated. ‘ By distillation 
it yields water, acid, oil, and ammonia ; the 
ashes containing a small proportion of fixed 
alkali ; and being either white or red, accord- 
ing to the proportion of pyrites contained in 
the substance. 
The oil which is obtained from peat has a 
very pungent taste, and an empvreumatic 
smell, less fetid than that of animal sub- 
stances, but more so than that of mineral bitu- 
mens: it congeals in the cold into a pitchy 
mass, which liquefies in a small heat : it rea- 
P E A 
dily catches fire from a candle, but burns less 
vehemently than other oils, and immediately 
goes out upon removing the external flame: 
it dissolves almost totally in rectified spirit of 
wine into a dark brownish-red liquor. 
It is evident that peat will vary as to com- 
position, according to situation and circum- 
stance ; and in almost every place will be 
found somewhat different. The following is 
an account ot the peat found near Newbury 
in Berkshire: Jt is a composition of the 
branches, twigs, leaves, and roots of trees, with 
grass, straw, and plants, particularly moss, 
which, having lain long in water, is formed in 
a mass so soft as to be cut through with a 
sharp spade. The colour is a blackish brown, 
and it is used in many places for tiring. 
There is a stratum of this peat on each side 
j ot the Rennet, near Newbury in Berks, 
: which is from about a quarter to half a mile 
! wide, and many miles long. The depth be- 
low the surface of the ground is from one foot 
to eight. Great numbers of entire trees are 
| found lying irregularly in the true peat. 
! They are chiefly oaks, alders, willows, and 
| firs, and appear to have been tom up by the 
j roots : many horses’ heads, and bones of se- 
veral kinds of deer ; the horns of the ante- 
lope, the heads and tusks of boars, and the 
: beads of beavers, are also found in it. Not 
many years ago an urn of a light-brown co- 
lour, large enough to hold about a gallon, 
was found in t lie peat-pit in Speen moor, near 
Newbury, at about 10 feet from the river, 
and four’ feet below the level of the neigh- 
bouring ground. Just over the spot where 
the urn was found, an artificial hill was rais- 
ed about eight feet high ; and as this hill 
consisted both of peat and earth, it is evi- 
dent that the peat was older than the urn. 
From the side of the river several semicircu- 
lar ridges are drawn round the hill, with 
trenches between them. The urn was broken 
to shivers by the peat-diggers who found it, 
so that it: could not be critically examined ; 
nor can it be known whether any thing was 
contained in it. 
I be ashes, properly burnt, are advan- 
tageously used for a manure. SeeHosBAND- 
RY. 
1 here are many low grounds, which, 
nearly on a level with small rivers, and some- 
times even below it, are alternately covered 
with earth and left by their waters, or admit 
them in such a manner as to be continually 
fermented by them. These grounds pro- 
ducing an enormous quantity of plants crowd- 
ed together, incessantly growing, and annu- 
ally accumulating layer upon layer, their soil 
becomes loaded to a greater or less depth 
with remains of vegetables, or herbaceous 
stalks, interwoven with each other in all di- 
rections, ot a black and coaly colour, and of 
a disagreeable or even fetid smell, which in- 
dicate a considerably advanced stage of ve- 
getable decomposition. 
1 hese remains, still solid and combustible, 
are known by -the name of turf or peat ; and 
the place from which they are taken are 
called bogs. Though peat consists of cohe- 
rent masses, belonging to a much larger mass 
ot one single piece of a subterranean depo- 
sit, yet by separating the filaments which 
compose their texture, we may distinguish 
several of the plants which have contributed 
to their formation. They are separable into 
long, soft, brown, or black stalks, some, 
times indeed of a blueish or violet colour, 
which have lost the natural consistence of the 
plants to which they belonged, and are mani- 
festly altered in their texture as well as in 
their nature. 
YY hen turf is heated in an apparatus for 
distillation, we obtain from it a yellow or red- 
dish fetid water, an extremely stinking oil, 
carbonate of ammonia, and carbonated hy- 
drogen gas of a very disagreeable smell. 
The residuum is a coal, frequently pyropho- 
ric, from which some salts may be extracted 
after incineration ; particularly muriates and 
sulphates of soda and potass, mixed with 
phosphate of lime, calcareous sulphate, and 
oxides of iron and manganese. Every per- 
son knows the manner in which turf burns in 
fire-places and furnaces, the ill smell it emits, 
and the reddish ferruginous ashes it leaves. 
Attempts have been made with some success 
to divest it of these inconveniences, by half- 
burning it in close vessels, so as to char it like 
wood. This process has certainly its advan- 
tage. It must be mentioned, however, that 
this charcoal is inferior to that commonly 
made from wood ; and that it is liable to take 
fire from the combined action of air and wa- 
ter, so that it ought to be kept for use in 
close places well secured. 
Peat therefore is in reality the residuum of 
plants or herbs half-decomposed, half-burned, 
induced almost to the state of charcoal, ana- 
logous in its nature to fossil wood, which is 
equally carbonaceous. It is used as fuel, 
where there is no other. It may be very 
useful in forges: its ashes are employed as 
manure. B^ bxiviation, salts ot use in the 
arts may be obtained from it. There are* 
some bogs which are found to contain like- 
wise sulphuret of iron, or pyrites. This 
compound, so combustible in moist air, heats 
them when they are exposed to it, and even 
occasions them to take fire. Some of them, 
such as those in the environs of Beauvais* 
are even capable of furnishing by lixiviation 
sulphate of iron, which is formed in them by 
exposure to the air. There is no doubt that 
most peats may be employed for obtainin'* 
from them by distillation an oil analogous to 
tar, as Berber proposed in 1683. 
PEBBLES, the name of a genus of fossils, 
distinguished from the flints by having a va- 
riety of colours. These are defined 0 to be 
stones composed of a crystalline matter de- 
based by earths of various kinds in the same 
species ; and then subject to veins, clouds, 
and other variegations, usually formed by in- 
crustation round a central nucleus, but some- 
times the effect of a simple concretion ; and 
veined like the agates, by the disposition 
which the motion of the fluid they were 
formed in gave their differently-coloured sub- 
stances. 
Idle variety of pebbles is so great, that a 
hasty describer would be apt to make almost 
as many species as lie saw specimens. A 
careful examination w ill teach us, however, 
to distinguish them into a certain number of 
essentially different species, to which all the 
re-t may be referred as accidental varieties. 
When we find the same colours, or those re- 
sulting from a mixture of the same, such as 
nature frequently makes in a number of 
stones, we shall easily be able to determine 
that these are all of them the same species. 
