POT 
?OT 
v o t m 
have a strong affinity for oxygen, when put 
into a solution of potass in water, especially 
if heat is applied, are gradually oxydized. 
This is the case with molybdenum, zinc, and 
iron. Tin also is oxydized in a very small 
proportion ; and this seems also to be the 
..case with manganese. 
It is capable of dissolving a considerable 
number of the metallic oxides ; and in some 
cases it deprives them of a dose of their 
oxygen. Thus, when poured upon the red 
oxide of iron it soon converts it into the black. 
The cause of this change is unknown. It has 
been ascertained, that the oxides of the fol- 
lowing metals are soluble in potass. 
Tin, Arsenic, 
Nickel, Cobalt, 
Zinc, Manganese, 
Antimony, Tungsten, 
Tellurium, Molybdenum. 
But the nature of these solutions has not 
hitherto been examined with any degree of 
attention ; though the subject is remarkably 
curious, and promises to throw light both 
■upon the nature of alkalies and metals. 
The affinities of potass are as follow: 
Sulphuric acid. 
Nitric, 
Muriatic, 
Phosphoric, 
Fluoric, 
Oxalic, . 
Tartaric, 
Arsenic, 
Succinic, 
Citric, 
Lactic, 
Benzoic, 
Sulphurous, 
Acetic, 
Saclactic, 
Boracic, 
Carbonic, 
Prussic. 
Potass has never yet been decomposed. Se- 
veral chemists, indeed, have conjectured, 
that it is a compound of lime and azote; and I 
some persons have even endeavoured to prove ' 
this by experiment; but none of their proofs j 
are at all satisfactory. We ought, therefore, j 
perhaps, in strict propriety, to have assigned j 
it a place among our enumeration of simple 
bodies in the article chemistry; but as it is 
excluded by most of the foreign chemists, we 
thought it "least likely to promote confusion j 
to follow their arrangement. Besides, we are 1 
certain, from a variety of facts, that all the j 
alkalies are compounds. One of them has 
actually been decompounded ; and the other 
two h ve been detect' d in the act of forma- 
tion, though the ingredients which compose 
them have not hitherto been discovered. 
Morveau and Desormes indeed announced, 
some time ago, that they considered potass 
as a compound of hydrogen and lime. Their 
chief proofs were the appearance of lime, I 
when the salt, composed of hyperoxygenized i 
muriatic acid and potass, is strongly heated 
with phosphoric acid in a crucible of platinum; 
and a manifest combustion together with the 
deposition of lime, when charcoal and potass 
are in like manner exposed to a strong heat 
in a platinum crucible. But these, and the 
other experimental proofs, being examined 
by Darracq, that accurate chemist ascertain- 
ed that the results obtained by Desormes and 
Morveau were owing, in most cases, to the 
impurity of the potass with which they had 
made their experiments; while in others, they 
had drawn wrong inferences from mistaken 
resemblances. Their hypothesis of course 
cannot be maintained. 
Potass is of the highest importance, not only 
in chemistry, where it is employed for a great 
variety of purposes, but also in many arts, and 
manufactures; as washing, bleaching, dying, 
glass-making, and others, as will appear on an 
inspection of these articles. It is employed 
also in surgery and medicine. 
POTATOE. See Solan um. 
POTENT, or Potence, in heraldry, a 
term for a kind of a cross, whose ends all ter- 
minate like the head of a crutch. 
POTENTILLA, si hcr-iveed, wild tansey, 
or cinquefoil , a genus of the pentagynia or- 
der, in the icosandria class of plants, and in 
the natural method ranking under tire 35th 
order senticosse. The calyx is decemfid ; 
there are five petals; the seeds roundish, 
naked, and affixed to a small dry receptacle. 
There are 32 species, the most noted are: 
1. The fruticosa, or shrubby potentilla, 
commonly called shrub-cinquefoil. "I bis is a 
beautiful deciduous flowering shrub, worthy 
a place in every curious collection. It grows 
wild in Yorkshire, and other northern parts of 
England, &c. but has been long cultivated in 
gardens as an ornamental shrub. 2. The 
reptans, or creeping common five-leaved po- 
tentilla, or five-leaved grass. 3 ■ Therupes- 
tris, or mountain upright cinquefoil, having 
the stalks terminated by small white flowers, 
4. The recta, or erect seven-lobed yellow 
cinquefoil, has the stalks terminated by co- 
rymbose clusters of yellow flowers. 5. The 
fragaroides, or strawberry-like trailing poten- 
tilla. This species bears "a great resemblance 
to the small sterile strawberry plants. 6. The 
argentea, silvery upright potentilla, with small 
yellow flowers, 
All these plants flower in June and July ; 
the flowers are composed each of five round- 
ish petals, and about 20 stamina. They are 
all very hardy, and may be employed in 
the different compartments of the pleasure 
ground. Their propagation is very easy. 
POTERIUM, garden burnet, a genus of 
the polyandria order, in the moncecia class of 
plants, and in the natural method ranking 
under the 54th order, miscelianese. The male 
calyx is tetraphyllous ; the corolla quadri- 
partite ; and there are from 30 to 40 stamina. 
The female calyx is tetraphyllous ; the corolla 
quadripartite ; "there are two pistils ; the berry 
is formed of the indurated tube of the corolla. 
There are five species, the most remarkable 
are : 1 . The sanguisorba, or common gar- 
den burnet. This species grows wild in Eng- 
land in chalky soils, but has been long culti- 
vated as a sallad-berb for winter and spring 
use, it being of a warm nature; the young 
leaves are the useful parts. It is perennial in 
root, and retains its radical leaves all the 
year, but the stalks are annual. 2. The 
nybridum, hybrid agrimony-leaved Mont- 
pelier burnet. This species often proves 
biennial ; but, by cutting down some of the 
stalks before they flower, it will cause it to 
multiply at bottom, and become abiding. 
3. Poterium spinosum, shrubby spinous bur- 
net of Crete, 
Burnet is of a cordial nature ; in summer, 
the leaves are used for cool tankards, to give 
the wine an agreeable flavour. Thepowder 
of the root of the first species is commended 
against spitting of blood, bleeding at the nose, 
dysenteries, and diseases attended with vio- 
lent secretions. In winter and spring, the 
young tender leaves are used in salads, Its 
uses as food for cattle are well known. 
POTHOS, a genus of the polyandria or- 
der, in the gynandria class of plants, The 
3Q2 
spatha or sheath is a simple spadix covered •’ 
there is no calyx, but four petals, and a s 
many stamina ; the berries dispermous. 
POTSTON E, a mineral found in nests and 
beds, and is always amorphous. Its structure 
is often slaty; fracture undulatingly foliated, 
greasy and brittle. Specific gravity from 
2.85 to 3.02. Colour grey, with a shade of 
green, and sometimes of red or yellow, some- 
times leek-green and sometimes speckled with 
red. Potstone is not much affected by the fire, 
and is made into utensils for boiling water : 
hence its name. It consists of 
38 magnesia 
38 silica 
7 alumina 
5 iron 
1 carbonat of lime 
1 fluoric acid. - 
POTTERY, the manufacture of earthen 
ware, or the art of making earthen vessels. 
In a general sense, therefore, it applies to all 
the different branches. See Delft- ware, 
Stone-ware, and Porcelain, &c. In a 
more, particular sense it is confined to the 
coarser kinds, such as the making of garden- 
pots, &c. The wheel and lathe are the chief 
and almost the only instruments in pottery ; 
the first for large works, and the last for small. 
The potter’s wheel consists principally in the- 
nut, which is a beam or axis, whose foot or 
pivot, plays perpendicularly on a freestone 
sole or bottom. From the four corners of this 
beam, which does not exceed two feet in 
height, arise four iron bars, called the spokes 
of the wheel ; which forming diagonal lines 
with the beam, descend, and are fastened at 
' bottom to the edges of a strong wooden cir- 
cle, four feet in diameter, perfectly like the 
felloe of a coach-wheel, except that it has 
neither axis nor radii, and is only joined to the 
beam, which serves it as an axis by the iron 
bars. The top of the nut is flat, of a circular 
figure, and a foot in diameter ; and on this is 
laid the clay which is to he turned and fa- 
shioned. The wheel thus disposed is encom- 
passed with four sides of four different pieces 
of wood fastened on a wooden frame; the 
hind-piece, which is that on which the work- 
man sits, is made a little inclining towards 
the wheel ; on the fore-piece is placed the 
prepared earth; ou tlie side-pieces he rests 
nis feet, and these are made inclining to give 
him more or less room. Having prepared 
the earth, the potter lays'a round piece of it 
on the circular head of the nut, and, sitting 
down, turns the wheel with his feet till it has 
got the proper velocity; then, wetting his 
hands with water, he presses his fist or his 
fingers-ends into the middle of. the lump, and 
thus forms the cavity of the vessel, continuing 
to widen it from the middle ; and thus turning 
the inside into form with one hand, while ho 
proportions the outside with the other, tho 
wheel constantly turning all the while, and he 
wetting his hands from time to time. When 
the vessel is too thick, he uses a flat piece of 
iron, somewhat sharp on the edge, to pare off 
what is redundant ; and when it is finished, it 
is taken off from the circular head by a' wire 
passed under the vessel. 
The potter’s lathe is also a kind of wheel, 
but more simple and slight than the former s 
its three chief members are an iron beam ur 
axis three feet and a half high, and two feet 
and a half in diameter, placed horizontally at 
tl$e top of the beam, and serving tp form th* 
