The home journal. (Winchester, Tenn.) 1858-188?, 1881-04-06
Thermometers.

Tho word thermometer means heat
measure, hence any instrument en-
ployed to measure heat should be called
thermometer. When very high tenn
peratures are to be measured, the in
struments employed are called pyrome-
tiers, or measures Of fire. Thermome-
tiers do not, Of course, measure the
quantity Of heat in body, but only tell
us the relative temperature. There arc
several forms Of thermometers, all based
upon the principle that cheat expands,
while cold contracts" Some substances
expand uneQually for equal increments
OF temperature, others expand SO slightly
that they fail to indicate small changes
of temperature both are untitled for
thermometers. II is believed that air
expands equally for equal changes of
temperature, and, rs this expansion is
quite considcrablc-l-273d part for each
degree ccntigrade--and rs it does not
become either liquid or solid under or
dlnary pressure, Mt any temperature
which We can produce, it is the sub
stance employed for the most accurate
measurements Of temperature. Any Of
the diiiicultly.condcnsiblc gases, oxygen,
hydrogen, marsh-gas, might be employed
lHStead OF air, but with no advantage
and with much inconvenience in their
Manufacture.
Next to air, the best material we have
IS mercury, which expands very evenly,
does not freeze readily, and boils at
comparatively. high temperature. For
temperatures below 10 deg. alcohol is
generally employed, although it is
claimed that glycerine could be used.
For temperatures above 300 deg G. air
thermometers alone are admissible;
and, for very high temperatures, where
glass begins to soften, they are made of
platinum.
The mercury thermometer being the
one usually employed in the arts, in
metoorology, III medicine, and in other
sciences, a few words in regard to the
manner Of making one may be of inter
est. A glass tube with very fine bore
has a suitable bulb, CT any desired form,
blown upon one end. At the other end
may be II bulb Of larger size, blown
merely for convenience IN filling. Meth
or bulb can be blown with tho mouth,
but with "A bellows, containing pure, dry
mir. A small capsule is flied with pure
mercury. heated to boiling to cxpel both
air and moisture While still hot the
second or temporary bulb is warmed to
cXpcl u portion Of the air therein the
open end is placed in the mercury, which
asccnds INTO tho bulb because the air
contracts on cooling. When sufficient
quantity of the hot mercury has been
introduced into this bulb the tube and
the other bulb are heated to expel part
of the air, and some Of the mercury,
which must be always kept hot to pre-.
vent it's chilling and thus breaking the
hot glass, enters the real bulb. BY re-
pcatlng the operation the bulb and stem
are completely filled with mercury,
which il then boiled to cXpcl every trace
Of air. The tube is now drawn out close
beneath the auxiliary bulb to fine
thread and cut off; the thermometer is
placed in Il bath heated Il few degrees
higher than the highest temperature
which the thermometer Is to show the
excess of mercury flows out, and the
point is closed with a fine blowpipe
fame. As the mercury contracts on
cooling it leaves perfect vacuum above
it,
Tho graduation is effected by putting
it into ice or snow, then in the steam
from boiling water, marking each Of
these points, dividing the space between
into 100 parts if it is to have u Celsius
or ccntigrade scale, into 80 if Reau-
muir or $50 if IA Fahrenheit. This grad
uaton ID carried ON in each direction to
the end Of the stem. On tho Fahren-
hcIt scale the freezing point is marked
80, on each of the other scales it is
marked zero. --ScicnHHc AHt,rical.