Dictionary of Chemistry [6th Ed.]

no rotational or vibrational energy).

According to *kinetic theory, the

thermodynamic temperature of such

a gas is given by T = 2U/3R, where R is

the universal *gas constant.

temperature-independent para-

magnetism(TIP)Orbital paramag-

netism that is independent of

temperature. In some substances TIP

can make the molecules paramag-

netic, although all the electrons in

the ground state are paired, if there

are low-lying excited states to which

electrons can readily move.

temperature scales A number of

empirical scales of *temperature

have been in use: the *Celsius scale

is widely used for many purposes and

in certain countries the *Fahrenheit

scale is still used. These scales both

rely on the use of Üxed points, such

as the freezing point and the boiling

point of water, and the division of

the fundamental interval between

these two points into units of tem-

perature (100 degrees in the case of

the Celsius scale and 180 degrees in

the Fahrenheit scale).

However, for scientiÜc purposes

the scale in use is the International

Practical Temperature Scale (1968),

which is designed to conform as

closely as possible to thermodynamic

temperature and is expressed in the

unit of thermodynamic temperature,

the *kelvin. The elevenÜxed points

of the scale are given in the table,

with the instruments speciÜed for in-

terpolating between them. Above the

freezing point of gold, a radiation py-

rometer is used, based on Planck’s

law of radiation. The scale is ex-

pected to be reÜned in the late 1980s.

temperingThe process of increas-

ing the toughness of an alloy, such as

steel, by heating it to a predeter-

mined temperature, maintaining it at

this temperature for a predetermined

time, and cooling it to room temper-

ature at a predetermined rate. In

steel, the purpose of the process is to

heat the alloy to a temperature that

will enable the excess carbide to pre-

cipitate out of the supersaturated

solid solution of *martensite and

then to cool the saturated solution

fast enough to prevent further pre-

cipitation or grain growth. For this

reason steel is quenched rapidly by

dipping into cold water.

temperature-independent paramagnetism 520

t

triple point of equilibrium hydrogen

temperature of equilibrium hydrogen when its

vapour pressure is 25/76 standard atmosphere

b.p. of equilibrium hydrogen

b.p. of neon

triple point of oxygen

b.p. of oxygen

triple point of water

b.p. of water

f.p. of zinc

f.p. of silver

f.p. of gold

13.81

17.042

20.28

27.102

54.361

90.188

273.16

373.15

692.73

1235.08

1337.58

–259.34

–256.108

–252.87

–246.048

–218.789

–182.962

0.01

100

419.58

961.93

1064.43

T/K t/°C

Temperature scales