A system of physical chemistry - Index of

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A system of physical chemistry - Index of

ATOMIC HEATS OF SOLIDS 55

wires which are connected to the heating spiral. By means of a Gaede

pump, together with a vessel of charcoal cooled in liquid air, a very

good vacuum is maintained in the glass vessel, so as to prevent any loss

of heat by convection. The calorimeter K {i.e. the substance itself),

together with the connecting wires, is brought to a certain temperature,

which is rapidly brought about by substituting hydrogen gas in place

of air (since the hydrogen conducts thermally so much better). The

hydrogen is subsequently removed, the vessel being evacuated. The

spiral resistance is of purest platinum. Its change in resistance v/ith

temperature was calibrated by comparison with an oxygen gas thermometer.

The calorimeter K varied in construction, according as to

whether the substance investigated conducted heat well or badly. The

first type shown in the figure is suitable when the substance is a metal.

Fig. 6.

(I,S

It consists of a small cylinder of the metal, having a cylindrical hole

drilled almost throughout its length. Into this a plug of the same

metal fits loosely, the heating spiral occupying the space between. To

insulate the spiral thin paraffined paper was employed, liquid paraffin

itself being finally poured in. The upper part of the plug is somewhat

thicker than the remainder, good thermal contact being thus obtained.

For substances which conduct heat badly the second form of calorimeter

was employed. A vessel of silver was used, the platinum spiral

being wound round a cylindrical sheet of silver, which served to spread

the heat rapidly. Electrical insulation of the spiral was maintained by

the help of shellac and thin silk. The platinum wire, on entering the

calorimeter, passes through a small insulating tube, and finally, after

passing through the body of the calorimeter, ends on the silver vessel,

to which a lead is attached. It was found that some air must be left

in the calorimeter itself (not in the pear-shaped vessel), so as to ensure

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