The Centigrade Scale

It was discovered fairly early, however, that the gas thermometer was quite useful since at ordinary pressure practically any gas would give about the same readings between two reference states. Suppose we adopt a centigrade scale, which strictly speaking simply means that we have 100 divisions between two fixed points. If we have a volume of gas Vo at the lower reference temperature and a volume Vioo at the upper reference temperature, then at other temperatures 

The quantity Vo/(Vioo — Vo) is experimentally determinable, and is found to be 2.73 for most gases when the two reference state temperatures are those of freezing water and boiling water. Then 

Thus if the linearity of the scale is maintained to very low temperatures, gases equilibrated with an object at —273 degrees on our centigrade g as scale will apparently have zero volume. This must represent an absolute zero on the scale, since we can t imagine negative volumes. In fact we cannot even imagine zero volume for finite quantities of gas (except for ideal gases whose particles occupy zero volume). So it also appears that our absolute zero is not physically attainable. 

The suggestion that temperature scales do have an absolute zero which is measurable, although perhaps not physically attainable, would go a long way toward removing the arbitrary nature of our temperature measurements. Fortunately, the truth of these ideas can be established independently of any consideration of individual temperature scales as we have above Lord Kelvin s demonstration of this will be considered later on. 

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There are great advantages to an absolute temperature scale that has its zero point at — 273°C. Whereas the zero of temperature in the Centigrade scale is based upon an arbitrary temperature, selected because it is easily measured, the zero point of the absolute scale has inherent significance in the kinetic theory. If we express temperatures on an absolute temperature scale, we find that the volume of a fixed amount of gas (at constant pressure) varies directly with temperature Also, the pressure of a fixed amount of (at constant volume) varies directly with temperature. And, according to the kinetic theory, the kinetic energy of the molecules varies directly with the absolute temperature. For these reasons, in dealing with gas relations, we shall usually express temperature on an absolute temperature scale. 

Make a table that contrasts the melting points and boiling points of LiF, Li, and F°, expressing the temperatures on the Centigrade scale. 

Hypothesize about why the Celsius temperature scale was previously called the Centigrade scale. 

Celsius (°C) A scale for measuring temperatures, also known as the centigrade scale, where the freezing point of water is 0°C and the boiling point 100°C. cement A natural or artificial fluid or semifluid substance, or mixture of substances, that hardens to act as an adhesive for binding solid surfaces together, cement, hydraulic A type of waterproof stony cement that sets even under water see pozzolana. 

A scale of temperature in which the interval between freezing point and boiling point of water is divided into one hundred degrees. This scale therefore came to be known as the centigrade scale, although the official designation is Celsius. Centrifuge... 

The centigrade scale was first proposed in 1694 by Renaldi. Centi is a Latin prefix meaning hundred. ... 

Scale of temperature. With a few exceptions all tepiperatures recorded in this book are on the Centigrade scale, and, for convenience, temperatures on the Centigrade scale are indicated by a numeral and degree mark without the letter C, as 18°. 

It is important to consider what happens when the substance or property employed is changed. For example, for a liquid in glass thermometer (using the Centigrade scale) ... 

On the commonly used Celsius scale (old name the centigrade scale), a temperature difference of one degree is the same as one degree on the Kelvin scale. The normal boiling point of water is 100°C the normal freezing point of water is 0°C and absolute zero is -273.15°C. 

Temperature scales such as the centigrade scale discussed in Chapter 1 are quite arbitrary, requiring a choice of two calibration points and the material and property used to interpolate between them. We saw that we could alternatively use a single-calibration-point scale based on a broad class of materials—the ideal... 

In 1742 Anders Celsius, a Swedish astronomer, developed the mercury centigrade thermometer. He chose the boiling and freezing points of water as calibration points. Curiously, he chose 0° for the high temperature and 100° for the low temperature. His choices were reversed in 1850 by Marten Stromer, also a Swedish astronomer. In 1948 the centigrade scale was officially renamed the Celsius scale. 

I. Convert into Fahrenheit readings the following readings on the centigrade scale —... 

If X represents any physical property which varies with temperature, Xo and Xioo are the values at 0 and 100 , respectively, on the centigrade scale the degree is then represented by the change tJitC-X ioo — Xo) in the given property. If X is the value of the property at any temperature t the magnitude of that temperature is then < , as given by... 

It follows, therefore, that when gases approximate to ideal behavior, i.e., at very low pressures, the differences in their thermometric properties disappear. This fact presents the possibility of devising a temperature scale which shall be independent of the thermometric substance, the latter being a hypothetical ideal gas. Such a scale is the so-called absolute ideal gas scale, in which the (absolute) temperature is taken as direcUy proportional to the volume of a definite mass of an ideal gas at constant pressure or to the pressure at constant volume. For convenience, the magnitude of the degree on the absolute scale is usually taken to be the same as on the centigrade scale ( 2b), so that the absolute temperature T on the ideal gas scale is given by... 

The centigrade scale of temperatures has been retained throughout the book. 

The change from the centigrade scale to the absohite temperature (Lord Kelvin, 1854) scale, which we have indicated above by the symbol T, is made as follows. It has been established experimentally that at constant pressure an ideal gas expands by 1/273 of its volume at 0° 0. when its temperature is raised by 1° C., so that we have, e.g.,... 

If we retain the unit of the centigrade scale in the absolute scale also, and Tf must differ by 100°. It follows that melting ice t == 0° C.) has the absolute temperature Tf = 273°, and boiling water t 100° C.) the absolute temperature = 373°. The zero of the absolute temperature scale lies therefore at —273° C. 

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