Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1892-04-03

advance which electrical science has made
within recent years. The superb dynamo.
which now employ steam or water on &
gigantic scale, to produce electricity, differ
from Faraday's simple model only in size
and form. The principle of the two is
identical.
An Electro Motor a Reversed Dynamo.
When preparations were in progress at
Vienna for the Exposition of 1873 work.
man saw pair of loose wires near him
which were attached to dynamo working
at distance. Close by stood another
dynamo quite idle. The idea occurred to
the man to connect the wires with this
neighboring apparatus He did so, and to
his astonishment it began Immediately to
revolve and soon attained a high speed. He
had unwittingly made a capital discovery
that the dynamo can be reversed-that the
very machine which gives out electricity
when it is supplied with motive power can
| give out motive power when it is supplied
with electricity. The reversibility OF the
dynamo, or rather of its predecessor, the
magneto-electric machine, was announced as
long ago as 1850 by Prof jacob, of st.
Petersburg. Notwithstanding the import
ance of the principle, it seems to have been
ignored until 1873, since which year the
world has been supplied with countless
electric motors for street railroads, factories,
| elevators and domestic uSS
In most systems tor propelling street cars
| by electricity the current is taken by a
| trolley from an overhead wire connected
with dynamos revolving at the stations.
Here and there throughout the Union diff
ferent system is in vogue. One for some
| months was tried as an experiment on the
Fourth avenue line in New York. In this
| system each car carries large storage bat
| terry made up of sheets of lead. As the
metal gradually undergoes chemical change
in an acid bath powerful current is pro-
| duced, as in an ordinary voltaic battery, and
this current turns the wheels of an electric
motor. When car has finished trip its
exhausted battery is taken into station,
where electricity is used to restore the lead
to its original state and so enable it to pro-
pei the car during another trip.
Storage and Electro-PIating.
Each operation is the reverse of the other.
As the car runs along the street the acid
bath in corroding the lead yields current,
precisely as is done by dissolving metal in
common battery. When the lead is after
ward brought to its first uncombined condi-
tion. the current sent in to do the work is
busy at nothing else than the reverse task
of electro-plating.
One of the first uses chemists found for
electricity after they were able to get it in
currents of great strength was the decom-
position of water into hydrogen and oxygen
gases. Sir William R. Grove, of London,
a man eminent in science as well as in law,
discovered that the gases disengaged would
readily recombine to form water again,
Welding in the process precisely the same
current of electricity.
1t is very singular fact, the reason for
which is yet far from clear, that water to be
decomposed by the electric current must not
be pure. The addition of little sulphuric
or other acid is essential, and this though
the added substance remains to the end of
the process seemingly unchanged. Let us
follow for moment the parallel between
this separation of water by electricity and
the artificial building up of sugars by the
same means. 1t will furnish us with
striking example of how natures rules work
both ways In a method devised by Brodie,
carbonic acid gas and hydrogen are SUBJ
jected to electricity silently discharged.
Formaldehyde is produced, and in the pres
ence of magnesia it condenses into sugar
of five or six fold the density of formalde-
hyde, but otherwise exactly similar in con-
stitution. Throughout the process of con-
densation the magnesia remains unaltered.
Chemical Marriage and Divorce.
As chemists more and more closely OBJ
serve the phenomena of combination they
are continually finding new cases of this
kind Carbon and phosphorus, conspicuous
among the most combustike substances we
know, are suspected of never uniting with
oxygen of strict purity. 1t would seem as
ifVhe union were a marriage whose bonds |
could only be Joined by third substance,
itself apparently unaffected by the act.
Carbonic oxide and oxygen under ordinary
circumstances form an explosive mixture,
but under ordinary circumstances there is
always q little moisture present, and with
out it, recent experiments with the gases
have shown, no explosion can occur. In
clearing up the intricate fashion in which
chemical marriage takes place, chemists are
bestowing careful study on chemical di-
vorce when electricity is the parting agent,
for one operation is held to be but the other
in reverse.
When the foundation of lighthouse or |
the vaulted arch of a cathedral is slowly |
taken apart stone by stone. the architects |
plan in piecing it together comes plainly |
into view, and at pleasure can be repeated in /
a new structure. In like manner the way in |
which a compound breaks up and the condi- |
tions surrounding the separation are closely |
observed by chemist, that he may build up |
an acid, an alcohol, or a sugar from its
simple elements. Many exquisite dyes and |
a lengthy list of compounds tor the relief of |
disease and pain are now artifciallv pre-
pared in the laboratory. With new re-
sources, both in material and method, We
may expect yet richer gifts in the future at
the hands Of the synthetic chemist.
Ice-Making by Means of Steam.
When the manufacture of ice by steam
was first established as an industry the an
nouncement had an air of paradox about it,
and yet the process depends upon the sim
pie principle we are considering, that rule
can work both ways. When steam expands
in the cylinder of an engine to do work it
loses heat precisely equal to the amount its
work could generate were it applied, let us
say, to rubbing metal plates together Now,
suppose the motive power to be used in
air. As a cylinder of air be-
comes more and more condensed it rises
in temperature. Let this heat be
by current of water, or in any
,ther convenient way, so that the air is no
warmer or cooler than the atmosphere. |
Then if the compressed air be permitted to
expand, and to do work in expanding, its |
will fall, and water or any
,ther substance surrounding it will be
chilled. The loss of heat is Just as real in |
he working cylinder of the steam engine, |
,ut SO high is the temperature there, even
It the lowest point, that the fact is masked, |
md thermometer of much higher than the
ordinary range is required to indicate it.
While steam or air in expanding in this
way descends in temperature, much more
lecided is the fall when liquid evaporates
-ery rapidly.
This everybody knows who has let alcohol,
II any of its preparations, drop on the hand.
When ammonia gas, of the kind not chem
cally combined with water, is powerfully
by a steam engine it takes on
i,a 1iouid form Tha oparatiop ;r ,,,,oL |