Re: IS IT VACUUM INSIDE THE THERMOMETER????????????

Dear ava:

Thanks for your question.
Before I answer it, let me tell you some words about temperature and 
thermometers:

Temperature is a quantity that establishes the thermal equilibrium between 
two bodies or systems, and it can not be measured directly. In practice we 
always measure some other quantity (the thermometric property of a 
thermometer) that varies according to a known function with temperature. 
Among the most used thermometric properties are: pressure of a gas (gas 
thermometers), length of a liquid column (liquid-in-glass thermometers), 
electromotive force (thermocouples), electric resistance (resistance 
thermometers) and spectral radiance (radiation thermometers). If you are 
interested in some of this topics you could visit the following links:
http://www.bipm.fr,
http://www.nist.gov,
http://www.npl.uk,
or consult: 
Quinn, T. J. Temperature, Academic Press, 1983.
If the response of a thermometer (its state equation) can be described 
using a function in which there are no quantities that depend on 
temperature in a unknown way, we say that the thermometer is a 
thermodynamic thermometer. Those thermometers need not to be calibrated, 
because its response is always known.
In the other hand, if the behavior of a thermometer is described using 
constants or variables that depends on temperature, we say that the 
thermometer is a practical one. Those thermometers require to be calibrated 
in order to provide meaningful responses.
Examples of thermodynamic thermometers are the gas thermometer and the 
radiation thermometer.
Liquid-in-glass thermometers, thermocouples, PRTs (Platinum Resistance 
Thermometers), RTDs (Resistance Temperature Devices) and thermistors are 
examples of practical thermometers.

Although you do not say so in your question, I think that you have in mind 
a liquid-in-glass thermometer, which is by far the most common type of 
thermometer. This kind of thermometers uses mainly mercury as its 
thermometric material, but for low temperature measurements (below -60 °C, 
approximately), alcohol is used instead.
The American Society for Testing and Materials (ASTM) (http://www.astm.org) 
publishes standards for fabrication and calibration of such thermometers.
Liquid-in-glass thermometers are designed to be used in one of three 
possible ways (see National Institute of Standards and Technology (NIST) 
special publication 250-23):
1.Partial immersion. These thermometers indicate temperatures correctly 
when the bulb (the deposit of mercury or alcohol) and a specified portion 
of the steam (the part were the scale is printed) are exposed to the 
temperature being measured. This length is marked in the steam using a line 
or a bump, or is indicated as a number in the "back" of the thermometer 
(the part of the steam in which the scale is not visible).
2.Total immersion. This type of thermometers is designed to indicate 
temperatures correctly when the bulb and all but 1 or 2 mm of the liquid 
column are immersed in the medium whose temperature is being measured.
3.Complete immersion. This kind of thermometers need to be completely 
immersed in the medium in order for them to give correct readings.

All of them can be used for low-temperature (below 150 °C ) and 
high-temperature (above 150 °C) measurements.
All high temperature thermometers should be filled with a dry inert gas 
such as nitrogen under sufficient pressure to prevent separation of the 
mercury at any temperature indicated on the scale. Total-immersion 
thermometers graduated above 150 °C must be filled with gas to minimize the 
distillation of mercury from the top of the column. An expansion chamber at 
the top of the capillary is essential for thermometers containing a gas, in 
order to prevent pressure building-up (which would damage the thermometer) 
when the mercury is advanced toward the top of the scale.
For thermometers graduated bellow 150 °C, a gas filling is optional but 
strongly recommended. The mercury column of a vacuous thermometer will tend 
to separate easily if the thermometer is inverted or subjected to a sudden 
shock.
I hope this answers your question

Regards
Jaime Valencia