The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1836-11-29 00:00:00

Nov. 29, 1s:;6.

either to gratify an enlightned and laudable curiosity, to 1
advance his temporal interests, or to enlarge the sphere
of useful knowledge; We have been much pleased with
the
rPport of the late lecture on chemistry, delivered at
the Mechanics' Institution, by Mr. John Hemming, of
London. Of that gentleman, as a lecturer, we have
heard frequently, and of his ability much to his praise.
We make these few prefatory observations to qualify the
comments we are about to offer upon his opening lecture.
What we think correct, which is the main character of
the lecture, we shall leave in the lucid statements of Mr.
It; to what we think obscure, or erroneous, we shall add
such illustration, or apply such correction, as we think ne
cessary ; and, in doing this, we are assured, that we are
doing no more than Mr. H. would have done, had he
been called upon to give explanation. To him we need
tender no apology.
Speaking of chemical attraction, Mr. H. truly ob
served, "that it was usual to divide the elementary bo-
dies into two classes, electro-positive and electro•nega-
tive;" but he adds, " this mode of distinction is arbitrary
and unscientific." Though sanctioned by this authority
of Mr. 11,, we confess that the distinction" does not

aPPear to us " arbitrary," notwithstanding the apparent
anomalies to which he refers; we say apparent, because
they are not real, but are reconcileable with the known
Itwir.of chemistry. We shall not seek for examples of
our 'own to' verify, our. position, but take that offered_ to us
b,YM-r• 1-I.—" Sulphur will combine with oxygen and hy-
drogen; in these cases," Mr. H. observes; the sulphur
is negative to the hydrogen, and positive to the pxygen.".
Tlns, whilst it declares a chemical truth, in no degree in-

validates the electro-chemical theory. It never was un
derstood that electrical characters indicated absolute bu

Illative qualities. Like every point except the-Centre,
of a magnet--to one extremity it will be north—to the
other extremity south. The most perplexing case in the
Play of. affinity as supposed to depend upon electrical

agency we ever remember to have seen, is that of passing
Btetkyrnver red hot iron, %hence result oxide of iron and
hYdrogen gas ; and then repassing the hydrogen gas on:
the red hot oxide of iron, whence there results the.ork
ginal metallic iron, and water. But.this we think capa-
ble of eXplanation upon known principles. Positive and
negative, as the very terms imply, are relatives,- just as
the
PPet,observ..es-r—
-" Ask where's the north.? :At York,.!tis.on the Tweed.;
Scotland, at the Orcades; -and there,
At Greenland." •
All these Places, and had there been .a thousand more,
with the exception of the extremes, are, and would have
been respectively north
,and smith of each. other. One
sturdy question, however, arises here, which we base ne-
ver seen solved : if the two bodies which are farthest
'zgunder in electrical habitudes ,combine, which implies
the greatest intensity of attraction, what cause can ever
separate them.?, We cordially unite in.the commenda.,
tiun so juitly,..paid to Dalton for his labours in perfecting
the Atomic Theory ; though to the. industry and skill of
I3erzelius we owe more, as regards the determination of
the 'Atomic weights._ ..
If Mr.. H., when
,he speaks of Mayow, meant that that
ingenious chemist was acquainted with carbonic acid gas,
"which escOPed with effervescence when oil of vitriol is
Mixed witli salt of tartar," we wholly, dissent from his opi-
nion---that honour belonged to Dr. Black, and Mayow's
knowledge of pneumatic chemistry was confined to ann.
thei gas, of Which lie treats, in his "Tractatus ---- de
Spiritu Nitro-dereo.”

"Potassium," says Mr. H., "is made by heating pot-
" 11 (which is a compound of oxygen, carbon, andinetal).
in a close vessel with charcoal." The process is correctly
stated, but we object to the rationale—the charcoal added
to the potash„does not take away the carbon of the car-
bonic acid united with the oxide of potassium, but sim-.
Ply 'deoxidfzeS the oxide of potassium, and then the car-
bonic acid is set free, according to.a law mentioned by
that " acids do not combine with inetals"—it is
possible, that the carbonic acid may be partially or en- -
y converted into carbonic oxide at the moment of li-
beration. Again, when "potassium is heated in carbonic
acid gas," something more happens, than the mere rege-
nerationof carbonate of potash—a portion of uncom-
bined carbon is also evolved.
" Nisi fiuida non agunt"—except bodies, one or both,
be in a state. of fluidity, they will not combine. This
maxim of- Black is not,as Dr. 4. justly observes, a uni-
versal law, if the instance mentioned by Mr. H. con-
firms it, viz., ".the mixture of tartaric acid and carbonate.
,of soda," the ease of sulphate of copper and acetate of
lead contradict it; and in both examples there is -present
water of crystalization.
With regard to the process of .obtahung lime, we be-
lieve that there is something, owing to the tendency to
form carbonic oxide, by uniting one atom of theoxygen
'4)f ate carbonic acid in the chalk.or marble with one atom
of the ignited carbon; and to.this conclusion we arrive,
because carbonate of lime ,_heated per se, in close tubes,
to an equal temperature, is more slowly, and more diffi-
cultly, decomp,osed and rendered caustic.
We are much inclined, to • doubt, whether in any case
of the chemical union of two metals, they are separable
by beat. We know. from many experiments upon spe--
culum metals, that no such separation takes place.
We finish our remarks upon the opening lecture. We
have much for which to thank Mr. Hemming ; and. if
the minds of our operatives can be turned from the bar-
ren wilds of politics to; .the fertile fields of chemistry,
the town of Liverpool, and. especial -the operatives them-
selves, will-have abundant cause to add their thanks to