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Page 16
By CHARLES K. GALLAGHER, Washington, N.C.
Any convenient number of percolators, made of rough boards, arranged
over a trough after the style of the old fashioned "lye stand,"
similar to the figure. Into these was placed the earth scraped from
around old tobacco barns, from under kitchens and smokehouses. Then
water or water and urine was poured upon it until the mass was
thoroughly leached or exhausted. The percolate was collected in a
receptacle and evaporated, the salt redissolved, filtered, again
evaporated, and crystallized from the mother water.
[Illustration]
* * * * *
THE TELEMETER SYSTEM.
By F.R. UPTON.
In this paper, read before the British Association, the author
explained that the "Telemeter System," invented by C.L. Clarke, of New
York, is a method by which the slow movement of a revolving hand of
any indicating instrument may be reproduced by the movement of a
similar hand at a distant place, using electricity to convey the
impulse. The primary hand moves until it makes electrical contact,
thus sending an impulse. It is here that all previous methods have
failed. This contact should be absolute and positive, for if it is
not, the receiver will not work in unison. The contact could often be
doubled by the jarring of the instrument, thus making the receiver
jump twice. Clarke has overcome this defect by so arranging his
mechanism that the faintest contact in the primary instrument closes
two platinum points in multiple arc with it, thus making a firm and
positive contact, which is not disturbed by any jar on the primary
contact. This gives the instruments a positive start for the series of
operations, instead of the faint contact which would be given, for
example, by the light and slowly moving hand of a metallic
thermometer. The other trouble with previous methods was that the
contact points would corrode, and, in consequence of such corrosion,
the instrument would fail to send impulses. Corrosion of the contacts
is due to breaking the circuit slowly on a small surface. This is
entirely remedied by breaking the circuit elsewhere than at the
primary contact, using a quick motion, and also by giving this
breaking contact large surface and making it firm. The instrument, as
applied to a thermometer, is made as follows: From the free end of the
light spiral of a metallic thermometer fixed at the other end, an arm,
C, is attached, the end of which moves over an arc of a circle when
the temperature varies. This end carries on either side of its
extremity platinum contacts which, when the thermometer is at rest,
lie between two other platinum points, A B, carried on radial arms.
Any variation in temperature brings a point on the thermometer arm in
contact with one of these points, and thus gives the initial start to
the series of operations without opposing any friction to the free
motion of the instrument. The first result is the closing of a short
circuit round the initial point of contact, so that no current flows
through it. Then the magnets which operate one set of pawls come into
play. The two contact points are attached to a toothed wheel in which
the pawls play, and these pawls are so arranged that they drive the
wheel whenever moved by their magnets; thus the primary contact is
broken.
[Illustration]
In the receiver there is a similar toothed wheel carrying the hand of
the indicating instrument, and actuated at the same moment as the
transmitter. The primary contacts are so arranged that the contact is
made for each degree of temperature to be indicated. This series of
operations leaves the instruments closed and the pawls home in the
toothed wheel. To break the circuit another wire and separate set of
contacts are employed.
These are arranged on the arms carrying the pawls, and so adjusted
that no contact is made until after the toothed wheel has moved a
degree, when a circuit is closed and a magnet attracts an armature
attached to a pendulum. This pendulum, after starting, breaks the
circuit of the magnets which hold the pawls down, as well as of the
short-circuiting device. As the pendulum takes an appreciable time to
vibrate, this allows all the magnets to drop back, and breaks all
circuits, leaving the primary contacts in the same relation as at
first. The many details of the instruments are carefully worked out.
All the contacts are of a rubbing nature, thus avoiding danger from
dirt, and they are made with springs, so as not to be affected by jar.
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