The San Juan islander. [volume] (Friday Harbor, Wash.) 1898-1914, 1903-09-10
THERMOMETERS MAKING.
How Boiling and Freezing Points Are
Found and Degrees Marked.


The making of a thermometer may
be either a delicate scientific operation
Or one of the simplest tasks or the
skilled mechanic, according to tho sort
of thermometer made. With the eX-
tremely sensitive and infinitely accur-
ate instruments designed for scientific
uses great care is taken and they are
kept in stock for months, sometimes
years, to be compared with instru-
ments that are known to be trust
worthy. But so much time cannot be
spent over the comparatively cheap
thermometer in common use, and these
are made rapidly, though always care
fully.
Mercury is generally used for scien-
titic instruments, but most makers pre-
fer alcohol because it is cheaper The
alcohol is colored red with aniline dye,
which does not fade. The thermom-
eter 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 blowpipe makes
the bulb on the lower end. The bulbs
are then filled with colored alcohol and
the tubes stand for twenty-four hours.
On the following day another workman
holds each bulb in turn over a gas jet
until the colored fluid by it's expansion
entirely fills the tube. 1t then goes
back into the hands of the glass blow
/ nr 10 al fha
the tip backward to make little hook,
which will help keep the tube in place
In the frame.
The tubes rest until some hundreds
Of them, perhaps thousands, are ready.
Then the process of gauging begins.
There are no marks on the tube and
the first guide-mark to be made Is the
freezing point, 80 degrees Fahrenheit.
This is found by plunging the bulb
into melting snow. No other thermom-
eter is needed for guide. for melting
snow gives invariably the exact freeZ-
ing point. This is an unfailing test for
any thermometer when accuracy may
be suspected. But melting snow is
not always to be had and little ma
chine resembling a sausage grinder is
brought into use. This machine 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 workman takes
them one by one from their bath, seiz-
ing each so that his thumb nail marks
the exact spot to which the fluid has
fallen. Here he makes scarcely per-
ceptible mark upon the glass with
fine file, and goes on to the next.
The tubes, with the freezing point
marked on each, now go into the hands
of another workman, who plunges the
bulb into a vessel filed with water
kept constantly at SO degrees. This
is marked like the others, and the tube
is now supplied with these guide
marks, each 80 degrees from the next.
With it's individuality thus establish
ed the tube goes into the hands of
marker, who fits it's bulb and hook
into the frame it is to occupy and
makes slight scratches on the frame
corresponding to the 80 degrees, Ga
degrees and SO degrees marks on the
tube.
The frame, whether it be wood, tin
or brass, goes to the gauging room,
where it is laid upon steeply sloping
table marked exactly in the position
for a thermometer of that size.
A long, straight bar Of wood or met
al extends diagonally across the table
from the lower right-hand corner to
the upper left-hand corner. On the
right this rests upon a pivot and on
the left it rests in a rachel, which lets
it ascend or descend only one notch
at time. Each notch marks the ex-
act distance Of two degrees.--London
Express.