triple point of water, which is 0.01°C above the

Degrees on the Rankine scale are the same size

freezing point of water, was chosen because it can

as degrees on the Fahrenheit scale, but the zero

be reproduced with much greater accuracy than

point on the Rankine scale is at -- 459.67°

either the freezing point or the boiling point. On

Fahrenheit. In other words, absolute zero is zero

this new scale, the triple point was given the value

on the Rankine scale and -- 459.67° on the

273.16 K. Note that neither the word *degrees *nor

Fahrenheit scale.

the symbol ° is used; instead, the units are

A second absolute scale, the Kelvin, is more

referred to as Kelvin and the symbol K is used

widely used than the Rankine. The Kelvin scale

rather than the symbol °K.

was originally conceived as an extension of the

In 1960 the triple point of water was finally

Celsius scale, with degrees of the same size but

adopted as the fundamental reference for this

with the zero point shifted to absolute zero.

temperature scale. The scale now in use is the

Absolute zero on the Celsius scale is -- 273.15°.

international Practical Temperature Scale of 1968

In 1954, a new international absolute scale was

(IPTS-68). However, you often see this scale

developed. The new scale was based upon one

referred to as the Kelvin scale.

fixed point, rather than two. The one fixed point

Although the triple point of water is

was the triple point of water --that is, the point

considered the basic or fundamental reference for

at which all three phases of water (solid, liquid,

the IPTS-68, five other fixed points are used to

and vapor) can exist together in equilibrium. The

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