Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1892-04-06
MAKING A Thermometer
IL Is Done Quickly but with Great Ac-
curacy by accomplished Workers.


the skilled mechanic, according to the
sort of thermometer made. says the
New York Sun. With the extremely
sensitive and minutely accurate in
struments 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 instruments that are known to
be trustworthy. But so much time
canpOt be spent over the compara-
! tivelT cheap thermometers in CON-
mon Use. and these are made rapidly,
though always carefully. The method
Of manufacture has been so system
atized within few years that the
very cheapest thermometer should
not vary more than fraction of de-
gree from the correct point.
Whether the thermometer is to be
charged with mercury or alcohola
whether it is to be mounted in a
frame of wood, pressed tin or brass,
the process is substantially the same.
Mercury Is generally used for scientific
instruments but most makers prefer
alcohol because it is cheaper. The
alcohol is colored red with an aniline
dye which does not fade.
/ The thermOmeter-maker buys his
glass tubes in long strips from the
glass factories The glass-blower on
the premises cuts these tubes to the
! proper lengths and with his gas-jet
and blow-pipe makes the bulb on the
lower end. The bulbs are then filed
with colOred alcohol and the tubes
stand for twenty-four hours.
On the following day another work
man holds each bulb in turn over a
gas-jet until the colored fluid by its
expansion entirely fills the tube. 1t
then goes back into the hands of the
glass blower. He closes the upper
end and turns the tip 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
( begins. There are no marks what
ever on the tube, and the first guide
mark to be made is the freezing point,
30 degrees Fahrenheit. This is found
by plunging the bulbs into melting
snow. No other thermometer is
needed 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 always TO be had, and little ma
chine resembling a sausage grinder is
Z l.. L..
shaves a block of ice into particles,
which answer the purpose as well as
snow.
When the bulbs have been long
enough in the melting snow a work
man takes them one 10y 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
goes on to the next.
The tubes, with the freezing point
marked on each, now go into the
hands of another workman, who
plunges them, bulb down, into a yes
sci filed with water kept constantly
at Ga degrees. A standard ther-
mOmeter attached to the inside of
this vessel shows that the temper
ature of the water is correct. An
other tiny file scratch is put at 81.
Then third workman plunges the
bulbs into another vessel of water
kept constantly at 90 degrees. This
is marked like the others and the
tube is now supplied with these guide
marks, each 32 degrees from the next.
a small table is then attached to
each tube, on which its number is
written-for, owing to unavoidable
variations in the bore of the tube,
each one varies slightly from the
Others.
With its individuality thus estab-
lished the tube goes into the hands
of maker, who fits its bulb and hook
into the frame it is to occupy and
makes slight scratches on the frame
corresponding to the 32, 81 and 90
degree marks on the tube. The
frame has a number corresponding
with the number of the tube and the
tube is iaId away in rack amid thou
sands.
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
80, "a and 90 degree marks must cor
respond with the marks upon the
table. If they do not the error in
marking is detected and the frame IS
sent back for correction.
A long, straight bar of wood or
metal extends diagonally across the
table from the lower right-hand cor
ner to the upper left-hand corner.
On the right this works upon a pivot,
and on the left it rests in a ratchet,
which lets it ascend or descend only
one notch at a time. That notch
marks the exact distance of two de-
grees. With the three scratches al
ready made for a basis the marker
could hardly make mistake in the
degrees if he tried.
The marks made upon the frame or
case are all made by hand with a
geometric pen and India ink if the
frame is of wood and with steel dies
if it is of metal. The tube bearing
the corresponding number is next at
tached to the frame, and the ther-
mometer is ready for the market
without further testing. Some
makers use only two guide marks,
but the best makers use three.
In the process of manufacture the
ordinary thermometer goes through
the hands of nineteen workmen, half
of whom are often girls and women.
Some of the larger concerns in and
near New York produce several hun
dred thousand instruments annually,
and on every one of them the pur-
chaser may see, if he looks closely.
the tiny scratch on the glass at 80,
"a and 90 degree marks. or some
where near them, as different makers
use different points.