The Foundations of Chemistry

(capillary) column extending upward. Mercury expands more than most other liquids as

its temperature rises. As it expands, its movement up into the evacuated column can be

seen.

Anders Celsius (1701–1744), a Swedish astronomer, developed the Celsius tempera-

ture scale, formerly called the centigrade temperature scale. When we place a Celsius

thermometer in a beaker of crushed ice and water, the mercury level stands at exactly 0°C,

the lower reference point. In a beaker of water boiling at one atmosphere pressure, the

mercury level stands at exactly 100°C, the higher reference point. There are 100 equal

steps between these two mercury levels. They correspond to an interval of 100 degrees

between the melting point of ice and the boiling point of water at one atmosphere. Figure

1-16 shows how temperature marks between the reference points are established.

In the United States, temperatures are frequently measured on the temperature scale

devised by Gabriel Fahrenheit (1686–1736), a German instrument maker. On this scale

the freezing and boiling points of water are defined as 32°F and 212°F, respectively. In

scientific work, temperatures are often expressed on the Kelvin(absolute) temperature

scale. As we shall see in Section 12-5, the zero point of the Kelvin temperature scale is

derivedfrom the observed behavior of all matter.

Relationships among the three temperature scales are illustrated in Figure 1-17.

Between the freezing point of water and the boiling point of water, there are 100 steps

(°C or kelvins, respectively) on the Celsius and Kelvin scales. Thus the “degree” is the

same size on the Celsius and Kelvin scales. But every Kelvin temperature is 273.15 units

above the corresponding Celsius temperature. The relationship between these two scales

is as follows:

__?K
°C273.15° or __?°C
K273.15°

Figure 1-16 At 45°C, as read on

a mercury-in-glass thermometer,

dequals 0.45d 0 where d 0 is the

distance from the mercury level

at 0°C to the level at 100°C.

1-12 Heat and Temperature 35

We shall usually round 273.15 to 273.

Figure 1-17 The relationships among the Kelvin,

Celsius (centigrade), and Fahrenheit temperature

scales.

100

 C

0

 C

d

d 0

273

283

293

303

313

323

333

343

353

363

373

0

10

20

30

40

50

60

70

80

90

(^100
212)
192

172

152

132

112

92

72

52

32

42

62

Boiling
point
of water
Freezing
point
of water
100
180

K Boiling C F
point
of water
Freezing
point
of water