Mr. John Frew, Langloan Iron Works, Coatbridge, has been successful in
perfecting a most ingenious pyrometer, an instrument which is capable of
continuously indicating every variation of temperature with a remarkable
degree of correctness. This instrument, which we here illustrate, has
already become known to a number of proprietors and managers of blast
furnaces; and on the occasion of the members of the Iron and Steel
Institute visiting Coatbridge, in connection with the meeting of that
body which was held in Glasgow last autumn, many persons became
interested in its construction and in the practical determination of
blast temperatures by its readings. Furthermore, Sir William Thomson has
expressed himself as being highly delighted with it on account of the
manner in which its use illustrates various beautiful scientific
principles.
The leading principle on which the construction of this pyrometer has
been based is the well-known law of the expansion of gases. Referring to
our engraving, it will be seen that at A is a pipe through which air from
the cold blast main is admitted into another and larger pipe, B, which
reaches nearly to the bottom of a water cistern, C. By means of the inlet
and outlet pipes, D and E, the height of the water in the cistern is
maintained at a uniform level. In this way there is provided a head of
water which retains within the pipe, B, a constant pressure of air,
equivalent to the head of water between the open end of that pipe and the
overflow at E. Any excess of pressure is prevented by means of the
open-ended pipe, which permits the air to escape by the central tube.
This latter prevents the agitation caused by the upward rushing air from
disturbing the level of the water in the cistern; and in order further to
assist this, the central tube is filled loosely in its upper part with
lead bullets or other suitable materials supported on a perforated plate.
The water level in the cistern is indicated by means of a glass gauge,
which is represented at G. To the upper end of the pipe, B, another pipe,
H, is attached. This is required for conveying the cold air to the
pyrometer proper, for the piece of apparatus above described is simply an
arrangement for securing a flow or current of air at constant pressure.
At any point where it is desired to fix a pyrometer, a connection is made
with the pipe last spoken of, by means of a small pipe such as is
indicated at J, into which is fixed a platinum or other metallic nozzle
of small bore, as shown at K. To this same pipe there is attached a
solid-drawn copper spiral heater or worm, L, which is fixed into the
place or the material the temperature of which it is desired to indicate.
Into the outlet of this worm another similar but larger nozzle, M, is
fixed. At N is shown a small pipe which is connected with the pipe, J, at
any convenient point between the inlet nozzle, K, and the spiral heater,
L. The other end of this pipe passes through the India rubber stopper of
a small cistern or bottle, O, which, when in use, is about two-thirds
filled with a colored liquid. It will be seen that the tube, N, only
passes through the stopper, so that it may convey pressure to the surface
of the liquid. At P is a glass tube which also passes through the stopper
and then to the bottom of the colored liquid; and as its upper end is
open, any variation of pressure in the spiral heater is directly
transmitted to the indicating column of colored liquid.
[Illustration: FREW'S PYROMETER.]
The operation of the instrument is as follows: As the cold blast used in
the apparatus would be useless for the working of the pyrometer if taken
direct from the cold blast main, owing to its irregularity of pressure,
the regulator that has been described is employed, and by its means an
absolutely steady flow of cold blast air at an unvarying pressure is
secured. The diameters of the inlet and outlet nozzles are so nicely
adjusted that, so long as both are at the same temperature, the outlet
nozzle, which is open to the atmosphere, will pass all the air that the
inlet nozzle can deliver without disturbing the pressure in the cistern,
O; but if heat be applied to the circulating air through the walls of the
spiral heater, the air expands in volume, and is unable to pass through
the outlet nozzle in its heated condition as rapidly as it is delivered
cold by the inlet nozzle. The consequence is that an increase of pressure
takes place in the apparatus between the two nozzles, and it is this
pressure that indicates the amount of heat that the air has taken up from
the hot blast pipe, in which the spiral heater is fixed. Then, again, as
this pressure is directly transmitted to the indicating liquid in the
cistern and the vertical tube immersed in it, a rise takes place in the
column which is in exact proportion to the expansion of the current of
blast passing through the spiral heater.
The method of graduating the indicator scales of the Frew pyrometer is
worthy of special notice. When the apparatus is fitted up, and before it
is permanently fixed in position, the spiral heater is placed in cold
water of known temperature, and the point noted at which the colored
liquid stands in the indicator tube. The water is then boiled, and the
rise in the liquid in the tube is again noted. Suppose, in the first
instance, the cold water temperature to be 62 deg. Fahr., and that, from
this point up to 212 deg. Fahr., the liquid to have risen 2¼ in. in the
tube; this is equal to 1½ in. per 100 deg. Fahr., and from these data a
scale is constructed, the correctness of which is easily verified by
transferring the spiral heater into an air bath or oil of high boiling
point, and then comparing the readings of the pyrometer scale with those
of a mercurial thermometer placed alongside of the spiral heater. By this
means it can be clearly demonstrated that, up to the highest point to
which it is safe to use a mercurial thermometer, the readings of the
pyrometer scale and that of the thermometer are identical.
While this pyrometer is particularly valuable for indicating the
temperature of hot blast stoves of every description, there are doubtless
many uses that will suggest themselves to persons engaged in various
industrial arts and manufactures. The apparatus is neat and substantial
in its parts, while it occupies very little space, is not at all liable
to derangement, and is entirely automatic in its action. A number of the
instruments have been in continuous use at the Langloan Iron Works, with
the most satisfactory results, for about eight months. The temperatures
they are graduated for vary according to the furnaces with which they are
connected and the kind of work to which these are
applied.--_Engineering_.
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An exchange gives the following very simple way of avoiding the
disagreeable smoke and gas which always pours into the room when a fire
is lit in a stove, heater, or fireplace on a damp day: Put in the wood
and coal as usual; but before lighting them, ignite a handful of paper or
shavings placed on top of the coal. This produces a current of hot air in
the chimney, which draws up the smoke and gas at once.
* * * * *
[FROM PHOTOGRAPHISCHE CORRESPONDENZ.]