Encyclopaedia Britannica > Volume 8, DIA-England

ELECTRICITY.
627
I nome- while the heats evolved from lead and tin are as 2:1; and
und from zinc and gold, and from brass and gold, as 2:1. 2e%,
.aws. silver and copper being regarded as the best conduc-
"Y'w' tors, from being the least heated by the explosion, the con¬
ducting power of
Gold to copper will be as 2: 3
Zinc or brass to copper or silver 1: 3
Platinum or iron to copper or silver..! : 5
Tin to copper or silver 1: 6
Lead to capper or silver 1:12
‘idly, That the conducting power of an alloy of gold and
copper, or gold and silver, is less than either metal se¬
parately ; and that the difference in the conducting power
increases with the quantity of the inferior conductor al¬
loyed ; and that tin and lead in alloy have a conducting
power equal to the mean of their two separate conducting
powers. And, kthly, that copper alloyed with an eighth
part of its weight of tin becomes as much heated by an
electrical explosion as iron.
slot! of Many beautiful experiments have been made by differ-
itallic ent philosophers, on the fusion of metallic wires. Mr
es‘ Kinnersley, in the presence of Dr Franklin, transmitted
the charge of a case of bottles through a fine iron wire.
After first appearing red hot, the wire was melted into
spherical drops like small shot. With a battery of thirty-
two square feet, Dr Priestley melted into globules wires
even so large as the seventieth of an inch in diameter,
sometimes placing them in tubes of glass, and sometimes
in paper. The most complete experiments, however, on
the fusion of wires were made by Mr Brooke, Van Ma-
rum, Baron Kienmayer, Mr Cuthbertson, and Mr Singer.
The following are a selection from their most successful
experiments.
The last of these experiments was made by Mr Cuth¬
bertson, and the last but one by Mr Singer. Mr Singer
found that the power of any coated surface to melt wires
varies with the thickness of the jars; which confirms the
conclusion of Mr Cavendish, that the quantity of electri¬
city necessary to charge different jars of the same extent
of coated surface is inversely as the thickness of the jars.
'■Sin- “ The effects of gradually increasing the power of the
r’s expe-charge,” says Mr Singer, “ when wires of the same length
nents. an(i dimeter are employed, are very remarkable. If the
wire be iron or steel, its colour is first changed to yellow,
then (by an increased charge) blue, by a further increase it
becomes red hot, then red hot and fused into balls ; it we
continue to increase the charge, it becomes red hot and
drops into balls, then disperses in a shower of balls, and
lastly disappears with a bright flash, producing an apparent
smoke, which, if collected, is a very fine powder, weigh¬
ing more than the metal employed, and consisting of it
and a portion of the oxygen of the atmosphere, with which
it has combined.”
The experiments of Van Marum were made with a
much greater extent of coated surface, and the effects
No. of
Bottles.
15
jars
Square
Feet of
Coated
Surface-
16
16
48
48
40
Grairs of
Repulsion
inBrooke’s
Electro
meter.
Length
of
Wire.
32
32
30
45
4
15
12
12
3
1
3
6
18
60
Diameter
of Wire.
yfo
rL
T7J5
T70
T7Lo
J
15 0
1
250
1
iTo
Efffect produced.
Steel wire melted.
Brass ditto ditto.
Steel ditto ditto.
Steel wire not ditto.
Steel wire melted.
Lead ditto ditto.
Iron ditto ditto.
Iron ditto ditto.
produced were consequently much more intense,
following are a few of his results :
The
Square Feet
of Coated
Surface.
130
130
225
225
225
225
225
225
225
Length of
the Wire.
180 inches
300
120
1.20
5
3-5
0-25
0-25
0-25
Diameter in
parts of
an inch.
TST
i
240
1
737
1
3TT
1
-T3:
33
33
33
Effect produced.
Iron wire melted.
Iron ditto ditto.
Lead ditto ditto.
Tin ditto ditto.
Iron ditto ditto.
Gold ditto ditto.
Silver ditto ditto.
Copper ditto ditto.
Brass ditto ditto.
Phenome¬
na and
Laws.
Van Ma-
rum’s ex¬
periments.
In the course of these experiments Van Marum observ¬
ed the curious fact, that when a charge of 225 square feet
of coated surface was transmitted through fifty feet of iron
wire, the jars were not entirely discharged, and the residual
charge was capable of melting two feet of the same wire.
With the view of determining the relative fusibility of
different metals, Van Marum applied the same electrical
charge to wires of different metals drawn to the same dia¬
meter. The following were the results with wires the 32d
of an inch in diameter.
Metals. Length of Wire Fused.
Lead 120 inches.
Tin 120
Iron 5
Gold 3^
Silver 4
Copper %
Hence he concludes that lead and tin are the worst me¬
tals for conductors, and copper, brass, and silver, the best.
M. Cavallo made some interesting experiments on theCavailo’s
fusion of grains of native platinum by means of electricity, experi-
He placed the grains in a groove one tenth of an inchroems.
deep, cut in the surface of a cake of wax. A battery was
discharged through a line of metallic grains thus arrang¬
ed, and in this way they were partially but decidedly
fused. He found the whiter grains to be more easily fused
than those of a dark-grey colour.
Another of the chemical effects of electricity is its power Oxidation
of promoting the combination of metals with oxygen, or, of metals,
what is the same thing, of oxidating them. Beccaria and
others had observed this property of electrical action, but
it is to Mr Cuthbertson and Mr Singer that we owe the
most complete series of experiments on this subject. The Mr Cuth-
apparatus used by Mr Cuthbertson is represented in Plate bertson’s
CCXIII. fig. 5, where AB is a cylinder of glass two inches apparatus,
and a half in diameter and eight inches high. A brass cap ccxill.
is screwed on the lower brass cap B, and in the interior of 5>
the vessel is fixed a small roller CD, on which is coiled a
quantity of wire attached to a pack-thread at intervals of
four inches. Into the centre of the upper cap A is screw¬
ed a brass tube F, about three inches long; the end of
the pack-thread and wire is pushed through it by means
of a long needle, and hog’s lard is placed in the tube so
that the thread and wire may move through it air-tight.
By this means the wire is stretched along the axis of the
glass cylinder, and when one length of it is exploded,
another is drawn forward by the contiguous pack-thread,
without opening the cylinder. The quantity of air ab¬
sorbed in the process is indicated by a gage. It consists
of a glass tube, about ten inches long, screwed into the
lower end of the stop-cock, and plunged in a vessel of