The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1892-05-14
Making Thermometers.

New York sun.
The making of thermometer may be
either delicate scientific operation, or one
of the simplest tasks of the skilled mechanic,
according to- the sort of thermometer made
With the extremely sensitive and mlnutely
accurate instruments designed for scientific
uses great care is taken, and they are kept
in stock Tor months, sometimes for years,
to be compared and reeomparcd with lustru-
mepts that are known to be trustworthy
But 50 much time cannot be spent over
the comparatively cheap thermometers In
common use, and these are made rapidly
though always carefully. The method OF
manufacture has been so systcmallzed WITHIN
few wears that the very cheapest Their
mometer should not vary more than frac-
ton of decree from the correct point.
Whether the thermometer Is to DC
charged with mercury or alcohol; whether
it is to be mounted in a frame OF WOOD
pressed tin or brass, the process Is substan,
tally 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 anlllne aye
which does not fade.
The Thermometer maker buys his glass
tubes in long strips from the glass factories.
The glassblower on the premises cuts these
tubes to the proper lengths, and with his
nas let and blowpipe makes the bulb on the
lower end. The bulbs are then filled with
colored alcohol, and the tubes stand for
..uor,,, four bnurS
On the following day another workman
holds each bulb in turn overa gas jet until
the colored fluid, by its expansion, entirely
fills the tube. 1t then goes back into the
hands of the glassblower 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.
MARKING THE TUBES.
The tubes now rest until some hundreds
of them, perhaps thousands, are ready.
Then the process of gauging begins. There
are no marks whatever on the tube, and
the first guide mark to be made is the
freezing point, 30 dogs. Fahrenheit. This
IL found by plunging the bulbs into melting
snow. No other thermometer is needed
for guide, for melting snow gives lnva-
riably 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
machine resembling Il sausage grinder Is
brought into use. This machine SLAVES
block of ice into 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
so that his thumb nail marks the exact
spot to which the fluid has fallen. Here
he makes scarcely perccptible mark upon
the glass with fine file, and goes on to
the next.
The tubes, with the freezing point marked
on each, now 90 into the hands Of another
workman, who pluBges them, bulb down,
into vessel filled with water kept con-
stantly at 81 dogs. A standard thermom-
eter attached to the inside of this vessel
shows that the temperature Of the water is
correct. Another tiny file scratch is put
at g.
Then Il third workman plungcs the bulbs
into another vessel of water kept constantly
at SO. This is marked like the others, and
the tube is now supplied with these guide
marks, each b dogs. from the next. 4
small tab is then attached to each tube, on
which its number is written-ior, owing to
unavoidable variations in the bore Of the
tube. each one varies slightly from the
others.
MARKING TIE CASES.
With its individuality thus established
the tube goes into the hands of Il marker,
who fits its bulb and hook into the frame
it is to occupy, and makes slight scratches
on the frame corresponding 10 the -, 81
and % degree marks on the tube. The
frame has number corresponding with
the number of the tube, and the tube is
laid away in rack amid thousands.
The frame, whether it be wood, tin OF
brass, goes To the gauging room, where it
is laid upon Il steeply sloping table, exactly
in the position marked for Il thermometer
of that size The b, "a and % degree
marks must correspond with the marks
upon the table. If they do not, the error
10 marking is detected and the frame is
sent back for correction.
\ long, straight bar Of wood ur metal
extends diagonally across the table from
the lower right hand corner to the upper
left hand corner. On the ri ht this works
upon Il pivot and on the left it rests in a
ratchet, which lets it ascend or descend
only one notch at time That notch
marks the exact distance of degs. With
the three scratches already made for
basis the marker could hardly make Il mis-
take in the degrees if he tried
The marks made upon the frame or case
are all made by hand with 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
attached to the frame, and the thermom-
eter is ready for the market without fur
ther testing. Some makers use onl y two
guide marks, but the best makers use three.
In the process of manufacture the ordi-
nary 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 hundred thousand instruments
annually, and on every one of them the
purchaser may see, if he looks closely, the
tiny file scratch on the glass at 81, 81 and
9G degree marks-Or somewhere near them,
as different makers use different points.