Encyclopaedia Britannica > Volume 8, DIA-England

ELECTRICITY.
605
PI ome. 2f inches wide at top, 1^ at bottom, 12± inches high, IJ
r md line thick, and weighing 16 ounces. At the first trial,
w% when the evaporation was very slow, the electricity, which
^r-/ was always very feeble, was t/irice negative, and thrice 0.
In a second trial it was also negative at first, but it be¬
came positive afterwards, and then vanished. In a third
trial the electricity was stronger and negative. The balls
of the electrometer now diverged 31 lines. It then be¬
came when the balls diverged -^jths of a line ; and
at the third projection, when it was still positive, the se¬
paration of the balls was so great as six lines.
Saussure’s next experiment was made with a cup of
porcelain, surrounded with sand in a clay crucible.
The electricity was negative, and the evaporation remark¬
ably rapid. Its intensity varied from 0 to 8 lines. The same
results were obtained with different porcelain crucibles.
When alcohol and ether were substituted for water, and
the silver crucible used, the electricity was negative.
With the former the greatest intensity was 1 line, and
with the latter 4*2 lines.
From these experiments Saussure infers, with great he¬
sitation, that the electricity is positive with those bodies
which are capable of decomposing water, or of being
themselves decomposed by their contact with water; and
that it is negative with those which are not decomposed.
He ascribed the result with silver to its being adulterated
with copper or other oxidable metals. The negative elec¬
tricity of burning charcoal he supposes to arise from the
readiness with which it loses its heat in contact with
water.
Saussure was unable to procure electricity either from
combustion or by suddenly exploding heaps of gunpow¬
der ; and all his attempts failed to develope electricity,
without ebullition, by evaporation, from large surfaces of
wet linen or white iron.
fltn- M. Cavallo followed Saussure in this inquiry, though
he does not seem to have been acquainted with the la¬
bours of the Swiss philosopher. He found that evapora¬
tion from iron produced negative electricity wdien the
iron was free from rust, but positive when it was very
rusty. He found also that white and clear flint glass
produced positive, while bottle glass evolved negative elec¬
tricity. From these various researches it is not easy to
deduce any thing like a general principle. The subject
indeed requires to be resumed, and great attention paid
to the chemical changes which take place during the pro¬
gress of the experiments.
Sect. III.— On the Electricity developed in Flame and
Combustion.
i tricity We have already seen, in the preceding section, that
J ime* MM. Lavoisier and Laplace obtained distinct indications
of electricity by the combustion of charcoal, and Volta in¬
forms us that he never failed to obtain it. Saussure, on
the contrary, as has been mentioned, never could deve¬
lope electricity either by combustion or the explosion of
gunpowder; and Sir Humphry Davy equally failed to pro¬
cure it by the combustion of iron or of charcoal in air or
in pure oxygen.
The electrical relations of flame have been subsequently
examined by M. Erman of Berlin and Professor Brande. M.
Erman concluded, from some experiments, that the insu¬
lated flames of wax, oil, alcohol, and hydrogen gas conduct
only positive electricity, while the flame of phosphorus con-
!n.
of
Lllo.
ducts only negative electricity. It was noticed by Mr Phenome-
Cuthbertson that when the flame of a common candle was na ami
placed halfway between two equal balls, the one positive- v_^aws*
ly and the other negatively electrified, the flame was at-
tracted to the negative ball, which consequently became
very warm, while the positive ball continued compara¬
tively cold.
In pursuing this idea Mr Brande placed the flames ofExperi-
various bodies between two insulated brass balls, one ofments °f
which was insulated positively and the other negatively, rande*
and obtained the following results.
Flames, Sf c. attracted to the Negative Ball.
Olefiant gas.
Sulphuretted hydrogen, slightly.
Arseniated hydrogen.
Flame of hydrogen, weakly.
Sulphuret of carbon.
Potassium in combustion, and its fumes.
Flame of gum benzoin.
Smoke of benzoin.
Charcoal emitted by camphor in combustion.
Resinous bodies in combustion exhibit the same pheno¬
mena as charcoal.
Flames attracted to the Positive Ball.
Sulphurous acid vapour.
A small flame of phosphuretted hydrogen, slightly.1
Fumes of white arsenic, slightly.
Large flame of carbonic oxide.
Vapour of burnt sulphur.2
Flame of phosphorus.
Vapour of phosphorus.
Stream of muriatic acid.
Stream of nitrous gas.
Vapour of benzoic acid.
In order to explain these phenomena, Mr Brande sup*
poses, that since some bodies are naturally negative, and
others positive, the positive ones will be attracted by the
negative ball, and the negative ones by the positive ball.
This conjecture was not confirmed by future observa¬
tion, and did not lead philosophers to any certain conclu¬
sions. The subject, however, was resumed by M. Pouillet,
who arrived at a general result, which explains in a satis¬
factory manner the errors and contradictions of preceding
observers.
The first point which occupied his attention w$s the Experi-
combustion of charcoal; and in his earliest experiments ments of
he found with surprise that he could sometimes obtain Eouil-
from it positive and at other times negative electricity, et*
while at other times he could not obtain the slightest
electrical indications. In explaining these discrepancies,
he supposed that one of the electricities was taken by the
charcoal, and the other by the oxygen or carbonic acid;
and in order to determine the truth of this supposition he
made the following arrangement. Having taken a cylin-Combus-
der of charcoal, he placed it vertically six or eight centi-tion of
meters below a plate of brass which rests upon one of the charcoa •
discs of the condenser. The charcoal having a commu¬
nication with the ground, was lighted at its upper end
without the fire reaching the lateral surface, and there
arose a column of carbonic acid, which struck the plate of
brass, and in a few seconds charged the condenser. The
electricity which the condenser received from the carbo¬
nic acid was always positive, whereas Lavoisier, Laplace,
and Volta made the electricity negative. When the char-
1 When the flame was large it was equally attracted by both balls.
* The direction of the flame could not be determined.