-
Articles/Ads
Article THE CHEMISTRY OF COMMON. THINGS. ← Page 7 of 9 →
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common. Things.
standard . usually taken in the measurcnieht of gpecihc heats is that of water , which is considered to be 1 , 000 , an easy method is afforded for determining the specific he ^ the quantity of ice which 140 , 000 grains will liquify , for that weight of water will dissolve 1 , 000 grains of ice . Thus the specific heat morOury is thirty-three , that of lead forty-two , that of iron about one hundred aiud twenty , that of alcoliola ^ ~
The specificheat of a compound is frequently less than the mean of those of its constituents . Thus , in the case of the mixture of water and sulphuric acid before alluded to , the rise of temperature may be accotmtcd for by the change in the specific heat of the compouhd . The liquids , when combined , having a coiisid < 3 rably less capacity for heat than when they were separate , the free or sensible
heat which they contain has a greater effect on their tenipera ^ nre whsii combined . It is the opinion of some that this change of specific heat is occasioned by an evolution of latent heat ; but this is by lid means clearly established . In . the chapter on flame , it was
stated that the increase of temperature was occasioned by ; a charige of latent into sensible heat , by which it was intended that a jportion of the heat which was previously inseh s ^ the thermometer , and the temperature of the mixture , which is the case , whichever theory be adopted ; but it is doubtful whether any cowtbined heat is separated by chemical union .
9 . Propagation ofIIeat .- — ' Jiedbtm ^ y be propagated or transferred from one body to another , in two ways , viz ., by radiation and con > den sation—by the first , when the bodies are at a distance apart ; and by the second , when they are in contact . The latter is also the means by which heat is transferred from one part of the same body to another . A heated body propagates its heat in straight lines in every direction , in the same manner as a luminous body radiates lisflit . A lighted
candle placed in the centre of a room transmits light to every object in the room to which a straight line from the candle can be drawn without encountering an opaque body . So , in like manner , if a red hot iron ball , be substituted for the candle , it will transmit heat to every object which "was before exposed to the light of the candle , Tlie walls , which were before illuminated , will iioav gradually become
warm , but a sheet of paper , or other opaque substance , held before a part of them will protect that part from the heat , as it would in the former case have shaded it from the light . Tlie use of fire screens is an application of this principle . The fire radiates heat throughout the room , but a screen placed before it will protect"all objects behind it from the influence of the radiation . It is by radiation that the
sun transmits light and heat to the earth and other planets . Most ofthe properties of rays of light are common to those of heat . The latter may bo transmitted and reflected , condensed and dispersed , refracted ancl polarised , in the same manner as light . A convex lens and a concave mirror possess the property of converging the rays of light which fall upon them to a focus , and heat maybe concentrated
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common. Things.
standard . usually taken in the measurcnieht of gpecihc heats is that of water , which is considered to be 1 , 000 , an easy method is afforded for determining the specific he ^ the quantity of ice which 140 , 000 grains will liquify , for that weight of water will dissolve 1 , 000 grains of ice . Thus the specific heat morOury is thirty-three , that of lead forty-two , that of iron about one hundred aiud twenty , that of alcoliola ^ ~
The specificheat of a compound is frequently less than the mean of those of its constituents . Thus , in the case of the mixture of water and sulphuric acid before alluded to , the rise of temperature may be accotmtcd for by the change in the specific heat of the compouhd . The liquids , when combined , having a coiisid < 3 rably less capacity for heat than when they were separate , the free or sensible
heat which they contain has a greater effect on their tenipera ^ nre whsii combined . It is the opinion of some that this change of specific heat is occasioned by an evolution of latent heat ; but this is by lid means clearly established . In . the chapter on flame , it was
stated that the increase of temperature was occasioned by ; a charige of latent into sensible heat , by which it was intended that a jportion of the heat which was previously inseh s ^ the thermometer , and the temperature of the mixture , which is the case , whichever theory be adopted ; but it is doubtful whether any cowtbined heat is separated by chemical union .
9 . Propagation ofIIeat .- — ' Jiedbtm ^ y be propagated or transferred from one body to another , in two ways , viz ., by radiation and con > den sation—by the first , when the bodies are at a distance apart ; and by the second , when they are in contact . The latter is also the means by which heat is transferred from one part of the same body to another . A heated body propagates its heat in straight lines in every direction , in the same manner as a luminous body radiates lisflit . A lighted
candle placed in the centre of a room transmits light to every object in the room to which a straight line from the candle can be drawn without encountering an opaque body . So , in like manner , if a red hot iron ball , be substituted for the candle , it will transmit heat to every object which "was before exposed to the light of the candle , Tlie walls , which were before illuminated , will iioav gradually become
warm , but a sheet of paper , or other opaque substance , held before a part of them will protect that part from the heat , as it would in the former case have shaded it from the light . Tlie use of fire screens is an application of this principle . The fire radiates heat throughout the room , but a screen placed before it will protect"all objects behind it from the influence of the radiation . It is by radiation that the
sun transmits light and heat to the earth and other planets . Most ofthe properties of rays of light are common to those of heat . The latter may bo transmitted and reflected , condensed and dispersed , refracted ancl polarised , in the same manner as light . A convex lens and a concave mirror possess the property of converging the rays of light which fall upon them to a focus , and heat maybe concentrated