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Article THE CHEMISTRY OF COMMON THINGS. ← Page 5 of 7 →
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The Chemistry Of Common Things.
distance from it . The earth constantly radiates its natural heat into spacer j and were the heat thus lost not replenished b y ^^ ^ e sources , its temperature would be gradually reduced to an indefinite extent . The only external source from which the earth appears to derive any sensible amount of heat is the sun .
The rise of temperature which in many cases accompanies chemical combinations , has already been noticed . When vapour is condensed , or liquids solidified , the latent heat which was required for maintaining them in the former ~ states , is evolved , and a rise of temperature is occasioned , which is communicated to the surrounding objects .
The heat produced by percussion and compression appears to be the result of a change in the specific heat of the body ,, consequent upon a condensation of its substance . Thus , when a nail is struck by a hammer , it is compressed into a smaller space ; its specific heat is at the same time dirninished , and the increase o ^
upon a decrease of specific heat follows . When air is compressed in a syringe , sufficient heat is evolved to ignite certain substances , such as German tinder , and in some cases the heat produced is so great , as to render the air luminous . The production of heat by however , be traced to the same cause as that by compression , for the specific heat of the bodies from which it is evolved does not appear to undergo any change by the process . There is great difference of opinion as to the manner in which animal heat is produced . The passage of electricity occasions heat . A feeble spark is sufficient to
ignite many inflammable substances , such as gunpowder , alcohol , & c , while with powerful discharges , or the electric light , the most striking results may be obtained . 6 . Measurement of Heat . —Sensation . — -Besides the influence exercised by latent and specific heat on the relation which the actual temperature of bodies bears to the absolute amount of heat contained in them , their apparent temperature , as perceived by the sense of feeling , is modified by various circumstances . In fact , the human body is about the most imperfect measurer of heat there is . In the
first place the perception of heat in objects in contact with the body is , dependent on the number of nerves which are exposed to its influence . If , for instance , we dip the whole hand into a basin of hot water , the water will feel hotter than if only one or two fingers were dipped into it . Again , the apparent temperature of objects , as perceived by aiiy part of the body , depends upon the temperature to which that part has been last exposed . And this may be illustrated
in a remarkable manner by a well known experiment . Take three basins , or glasses ; fill the first with the coldest water that can be procured , the second with lukewarm water , and the third with water as hot as can conveniently be borne . Place the left hand in the cold water , and the right hand in the hot water ; sensation of cold will of course be produced iu the left hand , and one of warmth in the right ; but this feeling will gradually die off , until at length , if the hands be kept still , scarcely any difference will be experienced jn the
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things.
distance from it . The earth constantly radiates its natural heat into spacer j and were the heat thus lost not replenished b y ^^ ^ e sources , its temperature would be gradually reduced to an indefinite extent . The only external source from which the earth appears to derive any sensible amount of heat is the sun .
The rise of temperature which in many cases accompanies chemical combinations , has already been noticed . When vapour is condensed , or liquids solidified , the latent heat which was required for maintaining them in the former ~ states , is evolved , and a rise of temperature is occasioned , which is communicated to the surrounding objects .
The heat produced by percussion and compression appears to be the result of a change in the specific heat of the body ,, consequent upon a condensation of its substance . Thus , when a nail is struck by a hammer , it is compressed into a smaller space ; its specific heat is at the same time dirninished , and the increase o ^
upon a decrease of specific heat follows . When air is compressed in a syringe , sufficient heat is evolved to ignite certain substances , such as German tinder , and in some cases the heat produced is so great , as to render the air luminous . The production of heat by however , be traced to the same cause as that by compression , for the specific heat of the bodies from which it is evolved does not appear to undergo any change by the process . There is great difference of opinion as to the manner in which animal heat is produced . The passage of electricity occasions heat . A feeble spark is sufficient to
ignite many inflammable substances , such as gunpowder , alcohol , & c , while with powerful discharges , or the electric light , the most striking results may be obtained . 6 . Measurement of Heat . —Sensation . — -Besides the influence exercised by latent and specific heat on the relation which the actual temperature of bodies bears to the absolute amount of heat contained in them , their apparent temperature , as perceived by the sense of feeling , is modified by various circumstances . In fact , the human body is about the most imperfect measurer of heat there is . In the
first place the perception of heat in objects in contact with the body is , dependent on the number of nerves which are exposed to its influence . If , for instance , we dip the whole hand into a basin of hot water , the water will feel hotter than if only one or two fingers were dipped into it . Again , the apparent temperature of objects , as perceived by aiiy part of the body , depends upon the temperature to which that part has been last exposed . And this may be illustrated
in a remarkable manner by a well known experiment . Take three basins , or glasses ; fill the first with the coldest water that can be procured , the second with lukewarm water , and the third with water as hot as can conveniently be borne . Place the left hand in the cold water , and the right hand in the hot water ; sensation of cold will of course be produced iu the left hand , and one of warmth in the right ; but this feeling will gradually die off , until at length , if the hands be kept still , scarcely any difference will be experienced jn the