San Antonio daily light. [volume] (San Antonio, Tex.) 1886-1907, 1895-08-23
Electrical Items Worth Remembering
TFrom the Scientific American

Dropping steel magnet, or VI
brating it in other ways, diminishes
its magnetism
tits said that steel containing -
per cent of of mangese cannot be
magnetised.
Flames and currents of very hot
air are good conductors of cleo
tricity. An electrified body, passed
near a fame soon loses its charge.
In charging secondary battery
the charging electro motive force
should not exceed the electro-mo-
tive force of the battery more than
5 per cent.
Lightning has an electro motive
force of $500, 900 volts and cur
rent of IA 600, 900 amperes. The
duration of the discharge of light.
ming is 10000 of a second.
The resistance of copper rises
about o. 81 per cent for each degree
Fahrenheit, OF about o. 50 for each
degree Cent.
A lightning rod is the seat of a
continuous current, so long as the
earth at its base and the air at its
apex are of different potentials-
The rate of transmission on At
lantic cables is F8 " ords of five let
tiers each per minute. With the
duplex" this rate of transmission
is nearly doubled.
The effect of age and of strong
currents on German silver is to
render it brittle. A similar charge
takes place in an alloy of gold and
silver.
To obtain the number of turns of
wire in an electro magnet, multiply
the the thickness of the coils by the
length and divide by the diameter
of the wire squared.
| A test for the porosity of porous
cells consists in filling the cell with
clean water and taking the per cent
of leakage. The correct amount OF
leakage is IFS per cent in "a hours.
If the air had been as good a
conductor of electricity as copper,
says Professor Alfred Daniel, we
would never have known anything
about electricity, for our attention
would never have been directed to
any electrical phenomena.
| A perfect'vacum is perfect in.
sulator. 1t is possible to exhaust
tube so perfectly that no electric
machine can send spark through
the vacuous space, even when the
space is only one centimeter.
| For resistance coils, formoderate
ly heavy currents, hoop iron, bent
into zigzag shape answers very we'll
| One yard of hoop iron, II inch wide
and 1872 inch thick measures about
I-Ioo of an ohm; consequently, 100
yards will be required to measure
an ohm.
The voltage of secondary bat
\ terry must always be equal to or
i slightly in excess to the voltage of
the lamp to be burned. For ex-
ample, 20 volt lamp will require
10 secondary cells. but 10 cells will
supply more than 20 lamps.
Compression of air increases its
dielectric strength. Cailletet found
that dry air compressed to a pres
sure of 40 or so atmospheres resis-
ted the passage through II of a
spark from a powerful induction coil
while the discharge points were
only o. SIS centimeter apart.
An accumulation with II plates,
| 10 IL inches is reckoned, in horse
power hours, equal to about one
| horse power hour. Taking this as
basis, it will require 6 cells for
one horse power for 6 hours, or 80
| cells for S horse power for the same
length of time.
To obtain the length of wire on
an electro. magnet, add the thick
ness of the coils to the diameter of
the core outside of the insulation,
multiply by 3.I4, again by the
length, and again by the thickness
of the coils, and divide by. the di-
ameter of the wire squared.
Blotting. paper, saturated with
a solution of iodide of potassium to
which little starch paste has been
added forms chemical test paper
for testing weak currents When
the paper (slightly damp is placed