The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1839-11-22 00:00:00

TRADESMEN'S INSTITUTION.

This admirable Institution is, we are happy to say, going
on prosperously, and rapidly and deservedly gaining public
confidence, and we are certain will secure liberal support.
The directors are working the Institution so as to afford eve-
ry advantage of improvement, amusement, and comfort to
the member's. Monsieur Girall, a native of Paris, is at the
head of the French department. Mercantile, literary, and
scientific knowledge can be acquired under competent gen-
tlemen. Tuesdays and Fridays are set apart for public lec-
tures. The following is the substance of his tenth lecture on
chemistry, delivered on Friday last by
C. G. FEINAGLE, ESQ., A.B.T.C.D.
The distinguishing characters of metals are their conduct-
ing powers with regard to heat and electricity, together with
a lustre peculiar to themselves, thence called the metallic
lustre. It was formerly imagined that great specific gravity
was a general property of these bodies, until Sir H. Davy
made his important discoveries of the bases of the alkalies
and alkaline earths, to which he applied the searching powers
of a large galvanic battery.
Potassium, the metallic base of potash, was discovered by
Sir H. Davy in 1807, by the above-mentioned agency, but in
too small quantity to be effectually examined. M. M. Jay,
Lussac, and Thenard, however, pointed out a means of ob-
taining it in sufficient quantity for experiment. Their me-
thod consisted in bringing fused potash into contact with iron
filings or turnings, heated to whiteness in an iron tube. At
that temperature the iron abstracts the oxygen from the pot-
ash, and the potassium being volatile, rises in vapour, and
may be condensed in coal vessels, or under the surface of
very-pure coal naptha, which, as it contains no oxygen, does
not re-convert the metal to potash. In place of pure potash,
the carbonate may be used. By heating the bi-tartrate of
close vessels, it is converted into an intimate mixture of car-
bonate of potash and charcoal. This mixture, with the ad-
dition of more charcoal or oil, may be distilled in an iron
bottle, and the metal collected as usual.
This metal, so far from being heavy, like the common me-
tals, is somewhat lighter than water, its specific gravity be-
ing about 0.86. It is malleable at common temperature ; at
150 degrees it fuses ; at 32 degrees, or the freezing tempera-
ture of water, it is brittle, and its fracture exhibits a crysta-
tine arrangement. When freshly cut, the metallic lustre is
very distinct ; but it tarnishes by a few seconds' exposure to
the air, from which it-attracts the oxygen. A piece of po-
tassium being thrown on the surface of water, attracts its
oxygen, liberating the hydrogen, which takes re, owing to
the great heat produced by the action. The purple colour of
the flame is due to the vapour of the metal.
Potaoh, or oxide of potassium, is formed whenever potas-
sium iYexposed to the action of oxygen. When this is done
in a dry vessel, the potash is anhydrous. A solution of pure
potash may be obtained by boiling carbonate of potash with
lime, which deprives it of its carbonic acid. By evaporating
this solution to dryness in a silver vessel, pure hydrate of
of potash is obtained. This, when melted and cast into
moulds, forms the potassa fuse of commerce, which, as well
as the solution, is much used in medicine and in the arts.
To free the solution from adhering carbonate of lime, it must
be filtered, and during filtration must be protected from the
carbonic acid of the air, which it absorbs rapidly. Mr. F.
drew a sketch of Mr. Donovan's filter, which is admirably
suited to this purpose.
Mr. F. now proceeded to explain the cause of a 'slight ex-
plosion which occurred when the potassium had ceased to
burn on the water. When this metal is burned with flame,
it becomes preroxide or tritoxide. When this pieroxide, pro-
duced by the heat, comes into close contact with the water,
it parts with oxygen, and becomes potash. The oxygen be-
ing liberated suddenly, caused the explosion. For this ex-
planation we are indebted to Mr. John Wilson, who found
that when the metal was introduced into strong and pure
nitric acid, this pwroxide fell to the bottom of the vessel as a
white powder, which, on the addition of water, was dissolved
with effervescence, owing to the escape of oxygen gas.
The chloride of potassium is the residue of the preparation
of oxygen gas from chlorate of potash, which latter is pro-
cured by passing chlorine gas into a solution of potash, when
both these salts are formed. The latter being less soluble,
is easily separated by crystalization. The nitrate is obtained
by exposing mixed animal and vegetable matter to air and
moisture, when the potash contained In the former unites
with the nitrogen and oxygen of the latter. It is chiefly used
in the manufacture of gunpowder. The per tentage of nitre
in any sample of gunpowder may be determined by washing
a known weight with hot water on a filter. On drying the
remaining charcoal and sulphur, we can estimate the nitre
from the loss of weight. The remaining mixture being treat-
ed with pure fuming nitric acid, the sulphur is converted into
sulphuric acid, the quantity of which may be determined by
muriate of barytes. as had been shown in Mr. F. s lecture on
sulphur.
Carbonate of potash is procured from the ashes of most
woods, and is commonly called pearl ash. It may be ob-
tained perfectly pure by heating to redness a mixture of the
bi-tartrate (cream of tartar) and nitre. To determine the
quantity of tree potash in a sample of ashes, the neutralizing
power of a known weight is tried by the alkillimeter, a simple
and accurate instrument.
Bi-carbonate may be obtained by passing carbonic acid gas
into a solution of the carbonate, from which it differs in be-
ing crystaline, and not deliquescent.
Ferryscyanuret of potassium, obtained by heating animal
matters with potash, is used in the arts and in chemistry as
a test for many metals.
We regret that want of space prevents us from following
the talented lecturer through the entire of this interesting
subject.
Mr. F.'s experiments on the colours of flame,prosdinugeueldarblyy
the nitrates of barytes and strontia, as well as those on the
detonating properties of chlorate of potash, were
beautiful and successful.

HEIGHT OF THE AURORA BOREALIS.-It appears from
paper read before the Royal Society by Dr. Farquharson,
that the height of the point to which the streamers seemed to
converge, and which is termed the centre of the corolla, was
by geometrical measurement of one aurora, 5693 feet aboie
the level of the manse at Alford, while the lower edge of the
same aurora was only 2481 feet above that level. The tops
of the Corean hills, which were immediately under the aurora,
are 1000 feet higher than the manse, so that the lower edge
•of the arch was only 1500 feet above those hills.—Dearden's
Miscellany.