The Pickens sentinel. [volume] (Pickens, S.C.) 1871-1903, 1881-04-07
Thermometers.

. ,Ihe word thermometer means q heat.
measure, hence any instrument en-
ployed to meSst1fe heat should be called
a thermometer. When very high tenn
peratures are to be measured. the In.
; struments employed are called pyrome-
ters, or measures of fire. Thermome
ters do not, of course, measure the
Quantity of heat In q body, but only tell
us the relative temperature. There are
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. It is believed that mir
expands equally for equal changes of
temperatttte, and, rs this expansion is
quite considerable-1-273d part for each
degree centigrade-and as it does not
pecome either liquid or solid under or
olhary pressure, at any temperature
which we can produce, it is the sub
stance employed for the most accurate
measurements of temperature. Any of
tue dltlicultly- y-condensible gases, oxygen,
hydrogen, marsh-gas, might be EMPLOYED
instead of air, but with no advantage
ana 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 O
comparatlvely-hi temperature. For
temperatures below 40 deg. alcohol is
generally employed, although it is
claimed that G. lycerine could be used.
FOR temperatures above 800 deg. Q. mir
tnnrn1 oil
and, Tor 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
meteorology, in medicine, and in other
sciences, few words in regard to the
manner of making one may be of inter
est. A glass tube with o very fine bore
has suitable bulb, CT my desired form
blown upon one end. At the other end
may be bulb of larger size, blown
merel y for convenience in filling. Meth
er bulb can be blown with the mouth
but with bellows, containing pure. drv
alr. A small capsule is filled with pure
mercury. heated to boiling to expel both
alr and moisture. While still hot the
second or temporary bulb is warmed to
eXpel portion Of the air therein the
open end is placed in the emercury. which
ascends into the 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 expcl O 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-
peating tho operation the bulb and stem
are completely filled with mercury,
which is then boiled to expel every trace
OF air. The tube is now drawn out close
beneath the auxiliary bulb to n fine
thread and cut off; the thermometer ia
placed in bath heated O few degrees
higher than the highest Temperatures
which the thermometer is to show the
excess of mercury flows out, and the
point is closed with fine blowpipe
flame. AS the mercury contracts on
cooling it leaves perfect vacuum above
it.
The graduation is effected by putting
1T 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 O Celsius
or centigrade scale, into 80 if Reau
mur or l8O if Fahrenheit. This grad
uation is carried on in each direction to
the end of the stem. On the Fahren-
heit scale the freezing point is marked
80, on each of tho other scales it is
marked zero.-Scicntifc Anaericon.
TI,A