Page 114 - My FlipBook

switch llie pyrometer hand will ascend the scale to a certain reading
which indicates the accuracy of the instrument (Fig. 119A). If the read-
ing on the scale shows a falling ofif it is evident that three new cells
should replace the old ones. This test must always be made when the
furnace is cold.
The "glower" that is placed within the muffle does not undergo
any change, for it conducts only a very feeble current and thus there is
practically no element or source of inaccuracy from its use. With every
muffle renewal new glowers are supplied, hence the accuracy of this
system is fully maintained. Experience in the use of new muffles also
has proven that there is no variation in one set of glowers as compared
with another. Another strong feature about this system is the fact that
a more stable recording instrument is employed.
The inventor devised this style of pyrometer in order to perfect a
pyrometer furnace that would be automatic in the fusing of porcelain,
for the "thermo-couple" system, he says, is impracticable for this purpose.
His furnace is at present the only one that is truly automatic in its work-
ing properties, and at the same time scientifically accurate in results.
The muffle construction is decidedly novel and unique. The outer
casing is a three-inch seamless brass tubing, which is placed in a steel
mold and filled with damp fireclay under hydraulic pressure. The
muffle proper is made from a special impervious snow white berline por-
celain. It is cylindrical in shape and is grooved on the outside as shown
in Fig. 121. This figure also shows the thin shell of chamber mounted
on a special mandrel with the wire wound in the grooves. Figs. 122 and
123 show the finished muffle, giving a front and rear view of same. Fig.
123 shows the main resistance wires and the w-ires leading from the
glowers. The most important feature concerning the construction of the
muffle lies in the manner by which the inner chamber and platinum wire-
ing are invested in the fireclay or outer chamber. There is a space, ap-
proximating about one-quarter of an inch between the platinum wire and
the fireclay chamber which is filled with very finely powdered silex.
The soft powder permits the wire to expand and contract freely and at
the same time removes all danger of contamination of the fireclay
aflfecting it. The front and rear of the muffle are sealed to a depth of
three-sixteenths of an inch with fireclay. Another notable feature is
winding of the wire about the inner porcelain shell. The coils are nearer
together at the front than in the rear (Fig. 121) so as to make the tem-
perature more nearly the same in the front section as that of the rear
portion of the muffle.
In the operation of the furnace attention is called to Fig. 119B,
which is the secondary hand of the pyrometer section. By turning this

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