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Article THE CHEMISTRY OF COMMON THINGS. ← Page 2 of 7 →
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The Chemistry Of Common Things.
general do at common temperatures unless they are exposed to light , either proceeding direct from its source , or reflected from other objects . But if a solid or liquid body be heated to a temperature of about 800 ° or 900 ° , it will give out light of itself , and so become
visible , in the absence of any other source of light . When a piece of iron , for instance , is raised to this temperature , it first appears of a dull red colour ; when still further heated , its light becomes of a brighter red , and * is capable of rendering objects near it visible ; a further Increase of heat causes the colour to become orange ^ and at length an intense white light is produced . When bodies are rendered luminous
in this manner , they are said to become incandescent , and the process of rendering them so is termed ignition . Experiments have proved that all bodies , iii the solid and liquid states , become incandescent at the same temperature ; but this law does not extend to gases—air , for instance , may be heated to such a degree that it renders red hot bodies with which it comes in contact , while the air itself emits no
light . But that gaseous matter may be heated to whiteness is evident in the ease of flame . It has already been remarked that the quantity of heat absorbed and reflected by bodies depends upon their colour . An explanation of this may be found in an exanlmation of the solar spectrum , the coloured rays of which are accompanied by a quantity of heat in
inverse proportion to their degrees of refrangibility . The least refrangible rays , the red , yellow , green , & c , are combined with a large amount of heat , while the blue and violet , which are the most refrangible , possess but little heating effect . Now a coloured body absorbs part of the rays falling upon it , and reflects the rest ; the quantities of heat which naturally are combined with the absorbed
and reflected rays being absolved and reflected with them . As the rays reflected by bodies is shown by their colour , the remainder being absorbed , the tendency of bodies to become heated by exposure to the sun or other source of heat , is in direct proportion to the refrangibility of the rays which are represented by their colour . A body of a dark and greatly refrangible colour—blue , for example—absorbing the
slightly refrangible rays , which have large corresponding quantities of heat , becomes easily heated ; while one of a light colour , such as yellow or red , throws off nearly all the heat which falls upon it , for it reflects the heating rays . A white surface reflects all or nearly all the light which it receives , and can , therefore , only with difficulty be heated by radiation ; but a black one , which absorbs all the rays , rises rapidly in temperature under the influence of solar light . Hence we see the advantage of wearing clothing of a light colour in summer , in order to throw off the heat of the sun from the body .
A similar law is found to prevail with regard to the transmission of heat . Bodies which transmit light are capable likewise ^ of transmitting heat , and if they be coloured , the heat which is transmitted corresponds with the colour of the transmitted light , the remainder , with the exception of a small quantity which is reflected ^
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things.
general do at common temperatures unless they are exposed to light , either proceeding direct from its source , or reflected from other objects . But if a solid or liquid body be heated to a temperature of about 800 ° or 900 ° , it will give out light of itself , and so become
visible , in the absence of any other source of light . When a piece of iron , for instance , is raised to this temperature , it first appears of a dull red colour ; when still further heated , its light becomes of a brighter red , and * is capable of rendering objects near it visible ; a further Increase of heat causes the colour to become orange ^ and at length an intense white light is produced . When bodies are rendered luminous
in this manner , they are said to become incandescent , and the process of rendering them so is termed ignition . Experiments have proved that all bodies , iii the solid and liquid states , become incandescent at the same temperature ; but this law does not extend to gases—air , for instance , may be heated to such a degree that it renders red hot bodies with which it comes in contact , while the air itself emits no
light . But that gaseous matter may be heated to whiteness is evident in the ease of flame . It has already been remarked that the quantity of heat absorbed and reflected by bodies depends upon their colour . An explanation of this may be found in an exanlmation of the solar spectrum , the coloured rays of which are accompanied by a quantity of heat in
inverse proportion to their degrees of refrangibility . The least refrangible rays , the red , yellow , green , & c , are combined with a large amount of heat , while the blue and violet , which are the most refrangible , possess but little heating effect . Now a coloured body absorbs part of the rays falling upon it , and reflects the rest ; the quantities of heat which naturally are combined with the absorbed
and reflected rays being absolved and reflected with them . As the rays reflected by bodies is shown by their colour , the remainder being absorbed , the tendency of bodies to become heated by exposure to the sun or other source of heat , is in direct proportion to the refrangibility of the rays which are represented by their colour . A body of a dark and greatly refrangible colour—blue , for example—absorbing the
slightly refrangible rays , which have large corresponding quantities of heat , becomes easily heated ; while one of a light colour , such as yellow or red , throws off nearly all the heat which falls upon it , for it reflects the heating rays . A white surface reflects all or nearly all the light which it receives , and can , therefore , only with difficulty be heated by radiation ; but a black one , which absorbs all the rays , rises rapidly in temperature under the influence of solar light . Hence we see the advantage of wearing clothing of a light colour in summer , in order to throw off the heat of the sun from the body .
A similar law is found to prevail with regard to the transmission of heat . Bodies which transmit light are capable likewise ^ of transmitting heat , and if they be coloured , the heat which is transmitted corresponds with the colour of the transmitted light , the remainder , with the exception of a small quantity which is reflected ^