The Palatka daily news. (Palatka, Fla.) 1884-1888, 1885-09-08
THERMOMETERS.
HOW THEY ARE MADE AND HOW
THEY ARE TESTED.
Uniformity of Bore EssentiaI-Shape and
Size Of the Bulb-The Graduation
of the Scale Scien-
tffic TaSIz.
iCHic1gC Herald.

The standard thermometer is = c0mbina-
ton of practical science and requisite work
manship, and for d first-class instrument
you have 20 pay many dollars as you pay
cents for the ordinary article, and then you
can't swear by it, because there many
Influences that affect the correctness of the
thermal register not to speak of the influ-
ences upon tho completed instrument by the
location of the latter
Numerous precautions required to
turn out n standard instrument. First of
all comes the choice OF tube. The bore
has To be carefully tested to see whether it
is of uniform capacity. In most of the tubes
the bore IS wider on one end than on the
other, although tho difference may DO 50
small that il requires very delicate opera
ti0ns to establish It. Quite frequently in a
hundrel pounds of the small tubes not more
than half p dozen are found which are abso-
luteiy trIe, because from the very nature of
the case the bore being produced by blow
ing, is in fact nothing else than a portion of
u very elongated After the tube has
boon selected the bulb is fixed by melting
one end OF the tuho in the flame of
alcohol lamp an blowing i'll at the other.
Then a small quantity of mercury is admit
tod. BY alternately cooling and heating
the bulb the very delicate thread of the
full IS driven from one end of the tubeto
the other, and during this process its length
the length alter in various situations the
workman knows that the capacity of the
bore Is not uniform.
To make the bulb Of the required size Is
solely matter of practice, machinery
has been invented to produce it automatic
ally. Ii the bulb is too large the instrument
viii register very Slow and if it is too small
it will not contain sufficient mercury to reg
lister very high temperature The shape of
the bulb is also OF Importance. The spheri-
cal shape is considered best adapted to re-
siSt the varying pressure of the atmosphere,
while cylindrical bllbS expose larger sur
faces of mercury, and are therefore pre-
forTel for more delicate instruments Very
small and thin bulbs for small quantities of
mercury have been made. but the Indicating
column rIus necessarily be SO fino as to lie
useless for practical purposes. Spiral or
coilcd tubular bulb were made so as to OBJ
tain Il greater and more even distribution of
surface exposeI to the atmosphere, but
these bulbs require such thickness of glass
that the effect sought to bs obtained is fEe-
qGautly nullified.
Shape and sizs of bulb and tube having
been determined, the filling is done in very
ingenious manner, and alike for both mer-
curry and alcohol thermal registers The
bulb is heated while the open end of the
tube is inbe ldel in the fluid, say mercury.
Upon allowing tho bulb to cool the atmo-
into the tube and this process is continued
until there is sufficient mercury in bulb and
tube. Ii Is of the create Importance that
tho mercury DO free from moisture and air,
aud t. accomplish this the metal is boiled
before the filling process. After the filing
it i boiled again II the tuba, AMI when the
explosion of mir and moisture Is complete
the workman dexterously closes the tube by
tho flame from his blowppe.
That finishes the purely mechanical part
of making tho t!arnlpm ter, for tho gradua-
ton of the scale may truly he termed n SCI
entiiic proceeding, at leG,t s, far a gradual
ing stan ard instrument is concern ii. In
the common therm Drneter the tube is fixed
to q scale which the degrees Marked
while in the standard III trumant the Gale is
engraved in the stem ITSELF in order to in
sure the greatest po -siblc accuracy of Obssr-
walton. Tho exact freezing point has to be
determined first, ana this j. done by means
OF melting ica, which has always tho same
temperatures, prdYitai t33 water from
which tie ice cnn%"aled IS pure. Tie bulb
AMI the lower portion Of the abs placed
in melting lee ana whore the mercury is
stationary the freezing point As marked.
This IS q comparatively oasy matter, but tn
Determine the boiling point is more difficult,
because 1t varies with the prossu of the
atmosphere.
Under certain con litiolt, combining GER
tule, The boiling point can be ascertained
with e2Iactnnss, bat ordinarily, even in good
instruments, the boiling point is approxi-
mately ascertlinel by actual experiment
A copper boiler Is provided with an open
cylinder in thu top serving vehicle for
the water to be- bDilel. Ths open cylinder
is just long enough to permit the insertion
of the tiermomsteT, that thu bulb does
not touch the water, an over this cylinder,
or rather arouli it. i p!acsl another to
protect the former from tho air. As the
vap1r Of the boiling watsr rises thu tube is
gradually lowered /, aI to kssp the top of
tho mercury just visible above the cylinder.
Who're the mercury remains stationary the
boiling point il obtained AMI marked off,
Subject to corrections for error
The space between the freezing AMI boil
ing point Is next divi ioI into certain num-
Der Of equal degrees. Fahrenheit makes y
degrees the freezing and 2l3 degrees the
boiling point; consequently the intermedi-
ato space is divided into ISJ degree. Gel
sius prop ]ses zero for the freez ng point and
100 degrees for tho boiling point Reaumur
has the freezing and boiling points separ-
arated by 50 III tead OF 100 degrees. Fair
cnheit arrived at his graduation by observ-
atoms and experiments male in Iceland.
.sstfEf.# 81. 4 Rival of The Olive.