Shenandoah herald. [volume] (Woodstock, Va.) 1865-1974, 1892-03-18
THERM0M METERS.
INTERESTING PROCESSES OF
THEIR MANUFACTURE.
Filling the Glass Tubes With Coll
ored Alcohol Gauging the
Instruments-Thc Tests
For Accuracy.

mechanic, according to the sort of ther-
mometer made. With the extremely
sensitive and minutely accurate instru-
ments designed for scientific uses great
care is taken, and they are kept in stock
for months, sometimes for years, to be
compared and recompared with the in
struments that are known to be trust
worthy. But so much time cannot be
spent over the comparatively cheap ther,
mometers in common use, and these arc
made rapidly, though always carefully.
The method of manufacture has been 50
systematized within few years that the
very cheapest thermometer should not
vary more than fraction Of degree
from the correct point.
Whether the thermometer is to be
charged with mercury or alcohol; wheth-
o er it is to be mounted in a frame of
wood, pressed tin, CT brass, the process
is substantially the sane. Mercury is
generally used for scientific instruments,
but most makers prefer alcohol, because
it is much cheaper. The alcohol is col
ored red with an anilinc dye which does
not fade.
The thermometer maker buys his glass
tubes in long strips from the glass facto-
ries. The glass blower on the premises
cuts these tubes to the proper lengths,
and with his gas jet AMI blow-pipe
makes the bulb on the lower end. The
bulbs are then filled with the colored
alcohol, and the tubes stand for twenty
four hours.
On the following day another work
man holds each bulb in turs over gas
jet until the colored fluid, by its expan-
sion, entirely fills the tube. 1t then goes
back into the hands oil the glass blower.
He closes the upper end, and turns the
lip backward to make the little glass
hook which will help keep the tube in
place in the frame.
The tubes now rest until some hun
dreds of them, perhaps thousands, are
ready. Then the process of gauging be-
gins. There are no MARKS whatever
upon the tube, nothing to show the tenn
peraturc of the atmosphere, and the first
guide-mark to be made is the freezing
point, 81 degrees Fahrenheit. This is
found by plunging the bulbs into melt
ing snow. No other thermometer is
needed here for a guide, for melting
snow gives invariably the exact freezing
point. This is an unfailing test for any
thermometer whose accuracy may be
suspected. But melting snow is not al
ways to be had, and little machine re-
sembling sausage grinder is brought
into use. This machine shaves a block
of ice into feecy, snow-like particles,
which answer the purpose as well as
snow.
When the bulbs have been long enough
in the melting snow workman takes
them one by one from their icy bath,
seizing each one so that his thumb nail
marks the exact spot to which the fluid
has fallen. Here he makes a scarcely
perceptible mark upon the glass with a
fine file, and goes on to the next.
The tubes, with the freezing point
marked upon each, now go into the hands
of another workman, who plunges them,
bulb down, into vessel fllei with
water kept constantlyat Ga degrees. A
standard thermometer attached to the in
side of this vessel shows that the tenn
perature of the water is correct. Another
tiny file-scratch is put at Ga.
Then a third workman pIunges the
bulbs into another vessel of water, kept
constantly at 96. This is marked like
the Others, and the tube is now supplied
with these guide-marks, each 32 degrees
from the next. A small tab is thea at
tached to each tube, on which its mum.
Der is written-for owing 10 unavoidable
variations in the bore of the tube each
one varies slightly from the others.
With its individuality thus established
the tube now goes into the hands of a
marker, who fits its bulb and hook into
the frame it is to occupy, and makes
slight scratches on the frame, cores
ponding to 80, Ga and SO degree marks
on the tube. The frame is given a mum.
Der corresponding with the number of
the tube, and the tube is laid away in
rack amid thousands OF others.
The frame, whether it be wood, tin or
brass, goes to the gauging-room, where
it is laid upon a steeply. .sloping table,
exactly in the position marked for
thermometer Of that size. The 30, G4
and &c degree marks must correspond
with the marks upon the table, IL they
do not the error in marking is instantly
detected, and the frame is sent back for
correction.
A long, straight bar Of wood or metal
xtends diagonally across the table, from
the lower nght-hand corner to the upper
left-hand corner. On the right this
works upon a pivot, and on the left it
rests in rachet, which lets il ascend
or descend only one notch at time.
That notch marks the exact distance of
two degrees. With the three scratches
already made for basis the marker
could hardly make mistake in the de-