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Article THE CHEMISTRY OF COMMON. THINGS. ← Page 2 of 9 →
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The Chemistry Of Common. Things.
The consideration of this ^ ^ s eight heads : — 1 . The effects of heat J as manifested in expansion , change of state , and chemical composition and decomposition . 2 . The forms taken by heat ; viz ., sensible and latent heat . 3 . The various m eans by which heat may be propagated .
4 . The relation of heat with light . 5 . The sources of heat . 6 . The meam ^ emmt of heat , by the thermometer , pyrometer , & c . 7 . The principal theories which have been advanced concerning the nature of heat . 8 . The application of the properties of heat to arts and manufactures . \ . EffidsofIwat . Expansion . — Although the form of solid bodies when not under the influence of externa , ! forces is invariable , their size
is not so . That varies with the temperature , increasing as heat is added , and decreasing as it is abstracted . All bodies occupy more space when hot than they do when cold . The operation of heating
increases the size of a body , while that of cooling diminishes it . ^ Suppose a plate of metal , perforated with a hole of a size Sufficient exactly to admit of a metal bar being placed in it , and having a notch cut in the side , equal in length to the bar . If the bar be heated , it will be increased both in length and thickness , so as no longer to enter the hole or fit the notch , but it will return on cooling to its
original dimensions . But if , on the other hand , its temperature be considerably reduced , it will not completely fill up the hole or the notch . In laying down the iron rails of railways , a space equal to a quarter of an inch is left between each length , to allow for their expansion in hot weather . Were this precaution not taken , the dilatation of the rails , after the sun had shone upon them for any length of time , would cause them to become crooked , to the danger of the trains passing over them .
Clocks and watches go at a slower rate in hot than in cold weather , the heat affecting the pendulum or balance wheel . The rate of the vibration of a pendulum depends on its length , a , long one swinging more slowly than one of a shorter length , and any increase in its length occasions a corresponding decrease in its rate , and consequently
in that ofthe clock whose motions it governs . Such an effect is produced by an occasion of heat . By combining different materials in the manufacture of the same pendulum , this effect may be neutralized . Such pendulums are termed compensating pendulums , and clocks furnished with them are unaffected by heat . Tlie perfection of chronometers is in part attained by the use of compensating balance wheels
formed on the same principle . Frequently in investing casks with tlie iron hoops which are to hold them together , the hoops are heated previously to fixing them in their places . This enlarges them 5 and in cooling they contract , and press the payts ofthe casks which they surround more closely together .
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common. Things.
The consideration of this ^ ^ s eight heads : — 1 . The effects of heat J as manifested in expansion , change of state , and chemical composition and decomposition . 2 . The forms taken by heat ; viz ., sensible and latent heat . 3 . The various m eans by which heat may be propagated .
4 . The relation of heat with light . 5 . The sources of heat . 6 . The meam ^ emmt of heat , by the thermometer , pyrometer , & c . 7 . The principal theories which have been advanced concerning the nature of heat . 8 . The application of the properties of heat to arts and manufactures . \ . EffidsofIwat . Expansion . — Although the form of solid bodies when not under the influence of externa , ! forces is invariable , their size
is not so . That varies with the temperature , increasing as heat is added , and decreasing as it is abstracted . All bodies occupy more space when hot than they do when cold . The operation of heating
increases the size of a body , while that of cooling diminishes it . ^ Suppose a plate of metal , perforated with a hole of a size Sufficient exactly to admit of a metal bar being placed in it , and having a notch cut in the side , equal in length to the bar . If the bar be heated , it will be increased both in length and thickness , so as no longer to enter the hole or fit the notch , but it will return on cooling to its
original dimensions . But if , on the other hand , its temperature be considerably reduced , it will not completely fill up the hole or the notch . In laying down the iron rails of railways , a space equal to a quarter of an inch is left between each length , to allow for their expansion in hot weather . Were this precaution not taken , the dilatation of the rails , after the sun had shone upon them for any length of time , would cause them to become crooked , to the danger of the trains passing over them .
Clocks and watches go at a slower rate in hot than in cold weather , the heat affecting the pendulum or balance wheel . The rate of the vibration of a pendulum depends on its length , a , long one swinging more slowly than one of a shorter length , and any increase in its length occasions a corresponding decrease in its rate , and consequently
in that ofthe clock whose motions it governs . Such an effect is produced by an occasion of heat . By combining different materials in the manufacture of the same pendulum , this effect may be neutralized . Such pendulums are termed compensating pendulums , and clocks furnished with them are unaffected by heat . Tlie perfection of chronometers is in part attained by the use of compensating balance wheels
formed on the same principle . Frequently in investing casks with tlie iron hoops which are to hold them together , the hoops are heated previously to fixing them in their places . This enlarges them 5 and in cooling they contract , and press the payts ofthe casks which they surround more closely together .