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Article THE CHEMISTRY OF COMMON. THINGS. ← Page 5 of 9 →
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The Chemistry Of Common. Things.
- 'CJwnii ^ upon chemical combination $ nd decomposition are too numerous and varied to be entered into here , but , so far as they relate to combustion ., they have been already treated of in the chapter on flame .
2 . Latent Meat . —If wetakea quantity of ice or snow , at a temperature below 32 ° ( 27 ; . for example ) , and place it near a source of heat , or in a warm room , the temperature will gradually rise till it attains 32 ° , as may be seen by a thermometer placed in it . Let us suppose that it reaches this point in one minute , that is at the rate of o per minute . When 32 ° is attained , the ice will begin to melt , and the thermometer will cease to rise . As soon as the last particle of
ice is dissolved , which will not occur till after the expiration , of twenty-eight minutes from the time it began to melt , the thermometer will again , rise at the same rate as before , viz ., 5 ° per minute . Mow , during the first minute , sufficient heat was passing into the ice to cause the thermometer to rise 5 , and during the thirtieth and each succeeding minute , the same quantity of heat was passing into the water , for the thermometer rose at the same rate as before , hut during the twenty-eight minutes which intervened , the thermometer remained
stationary " , although it is evident that the same quantity of heat must have been passing then as at other times . While the ice was melting , therefore , sufficient heat was entering it to have raised the thermometer , had it not been for this change , 140 degrees . What then have become of these 140 degrees ? We can only , account for them by supposing that they have been taken up in converting the ice into
water , and entering into combination with the substance of the water have become imperceptible by the thermometer . . The heat thus absorbed is therefore called latent or hidden heat . If an ounce of ice at 32 ° be mixed with the same quantity of water at 1 . 72 ° , the ice will gradually melt , till at length two ounces of water are obtained , which
will have the temperature of 32 ° . In this instance , 140 ° of the hot water were abstracted , but the only effect they had upon the ice was to melt it , without raising its temperature . There is therefore the same difference of heat between ice at 3 . 3 ° and water at 32 ° , as
there is between water at 32 ° , and water at 172 ° , which proves as before , that in converting ice into water , as much heat is absorbed as would raise an equal weight of water 14 . 0 ° in . temperature . To prove
more clearly that this heat is actually absorbed , we may cool tho water down till it freezes . As soon as ice begins to form , it will preserve ife temperature of 32 ° , notwithstanding that heat is constantly beam abstracted , and will continue to do so until the whole of the water is converted into ice .
A similar phenomenon occurs in . the conversion of water into steam . It will take one thousand times as long to convert a given quantity of water into steam , as it would , in the same circumstances , to raise the water one degree in temperature , although a thermometer placed in the steam will give the same indication as when placed in the boiling water ; so that in this process a quantity of heat 13 ab-
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common. Things.
- 'CJwnii ^ upon chemical combination $ nd decomposition are too numerous and varied to be entered into here , but , so far as they relate to combustion ., they have been already treated of in the chapter on flame .
2 . Latent Meat . —If wetakea quantity of ice or snow , at a temperature below 32 ° ( 27 ; . for example ) , and place it near a source of heat , or in a warm room , the temperature will gradually rise till it attains 32 ° , as may be seen by a thermometer placed in it . Let us suppose that it reaches this point in one minute , that is at the rate of o per minute . When 32 ° is attained , the ice will begin to melt , and the thermometer will cease to rise . As soon as the last particle of
ice is dissolved , which will not occur till after the expiration , of twenty-eight minutes from the time it began to melt , the thermometer will again , rise at the same rate as before , viz ., 5 ° per minute . Mow , during the first minute , sufficient heat was passing into the ice to cause the thermometer to rise 5 , and during the thirtieth and each succeeding minute , the same quantity of heat was passing into the water , for the thermometer rose at the same rate as before , hut during the twenty-eight minutes which intervened , the thermometer remained
stationary " , although it is evident that the same quantity of heat must have been passing then as at other times . While the ice was melting , therefore , sufficient heat was entering it to have raised the thermometer , had it not been for this change , 140 degrees . What then have become of these 140 degrees ? We can only , account for them by supposing that they have been taken up in converting the ice into
water , and entering into combination with the substance of the water have become imperceptible by the thermometer . . The heat thus absorbed is therefore called latent or hidden heat . If an ounce of ice at 32 ° be mixed with the same quantity of water at 1 . 72 ° , the ice will gradually melt , till at length two ounces of water are obtained , which
will have the temperature of 32 ° . In this instance , 140 ° of the hot water were abstracted , but the only effect they had upon the ice was to melt it , without raising its temperature . There is therefore the same difference of heat between ice at 3 . 3 ° and water at 32 ° , as
there is between water at 32 ° , and water at 172 ° , which proves as before , that in converting ice into water , as much heat is absorbed as would raise an equal weight of water 14 . 0 ° in . temperature . To prove
more clearly that this heat is actually absorbed , we may cool tho water down till it freezes . As soon as ice begins to form , it will preserve ife temperature of 32 ° , notwithstanding that heat is constantly beam abstracted , and will continue to do so until the whole of the water is converted into ice .
A similar phenomenon occurs in . the conversion of water into steam . It will take one thousand times as long to convert a given quantity of water into steam , as it would , in the same circumstances , to raise the water one degree in temperature , although a thermometer placed in the steam will give the same indication as when placed in the boiling water ; so that in this process a quantity of heat 13 ab-