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Article THE CHEMISTRY OF COMMON THINGS. ← Page 3 of 7 →
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things.
¦ ¦ ¦¦¦ . ¦ .: ¦ % /¦ being absc & rbed . A piece of bluo glass , for Example , transmits but little heat , and absorbs a large qua in telescopes , to protect the eye from the effocts of the heat of the s condensed by the lenses ; and they have in some eases been cracked in consequence of the quantity of heat absorbed .
A very striking illustration of the effect of the heat-absorbing quality of bodies of a dark colour , is related by the ^ MoM as having occurred in the offices of the Magnetic Telegraph Conipany at Greenock , situated in the Gity of Glasgow Buildings in Gathcart Street . The window consists of two very large sheets of plate glass , enclosed in thick cast iron frames , and placed together in
the form of an obtuse angle . The name of the company had been gilded on the inside of the ^ glass , and a coating of dark green was spread over the lower part of the glass , to serve the double purpbse ^ a window shade and to form a ground for the gilded letters . A short time after this was done both panies of glass were cracfced , an effect which the parties concerned were a ^
supposing that it was caused by the settling down of the building . -Fresh sheets of glass were inserted , the name gilded , and the glass painted in the same manner as before , vrift As the window is greatly exposed to the sun , the North JBritish DoMy Mail points to the unequal expansion of different portions of the glass , in consequence of their being differently a by the heat of the sun , as the most probable cause of the breakages . This
supposition is strengthened by thefact that it was observed on each occasion that the cracks were chiefly confined to the portions of the glass which were painted . The colourless parts of the glass would obstruct but a very small portion of the rays of heat which fall upon them from the sun , just as , when the hand be applied to a glass window through which the sun is shining it feels scarcely warm , although a dark object placed behind the window soon becomes heated to such a degree that it cannot be touched without inconvenience . In the case in
question , the paint which was spread on the lower part of the glass being of a very dark colour , absorbed a large quantity of the heat contained in the solar rays , and becoming greatly raised in temperature communicated its heat to those portions of the glass with which it was in contact . The uncovered parts of the glass retained but little heat , and consequently remained comparatively cool | and the
unequal expansion of different portions occasioned fracture , as is generally the case when glass is differently heated in its various parts . The circumstance of the glass having been enclosed in an iron framework must have increased the tendency of the glass to break , for the great conducting power of the iron would render the edges much colder
than the rest of the glass . The journal above alluded to suggests , as preventive of the occurrence of similar accidents , —first , that the framework of all large plate glass windows that are much exposed to the sun should be formed of wood ; and secondly , that the ? painted portion of the Avindow should not be a part of the larger sheet , but
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things.
¦ ¦ ¦¦¦ . ¦ .: ¦ % /¦ being absc & rbed . A piece of bluo glass , for Example , transmits but little heat , and absorbs a large qua in telescopes , to protect the eye from the effocts of the heat of the s condensed by the lenses ; and they have in some eases been cracked in consequence of the quantity of heat absorbed .
A very striking illustration of the effect of the heat-absorbing quality of bodies of a dark colour , is related by the ^ MoM as having occurred in the offices of the Magnetic Telegraph Conipany at Greenock , situated in the Gity of Glasgow Buildings in Gathcart Street . The window consists of two very large sheets of plate glass , enclosed in thick cast iron frames , and placed together in
the form of an obtuse angle . The name of the company had been gilded on the inside of the ^ glass , and a coating of dark green was spread over the lower part of the glass , to serve the double purpbse ^ a window shade and to form a ground for the gilded letters . A short time after this was done both panies of glass were cracfced , an effect which the parties concerned were a ^
supposing that it was caused by the settling down of the building . -Fresh sheets of glass were inserted , the name gilded , and the glass painted in the same manner as before , vrift As the window is greatly exposed to the sun , the North JBritish DoMy Mail points to the unequal expansion of different portions of the glass , in consequence of their being differently a by the heat of the sun , as the most probable cause of the breakages . This
supposition is strengthened by thefact that it was observed on each occasion that the cracks were chiefly confined to the portions of the glass which were painted . The colourless parts of the glass would obstruct but a very small portion of the rays of heat which fall upon them from the sun , just as , when the hand be applied to a glass window through which the sun is shining it feels scarcely warm , although a dark object placed behind the window soon becomes heated to such a degree that it cannot be touched without inconvenience . In the case in
question , the paint which was spread on the lower part of the glass being of a very dark colour , absorbed a large quantity of the heat contained in the solar rays , and becoming greatly raised in temperature communicated its heat to those portions of the glass with which it was in contact . The uncovered parts of the glass retained but little heat , and consequently remained comparatively cool | and the
unequal expansion of different portions occasioned fracture , as is generally the case when glass is differently heated in its various parts . The circumstance of the glass having been enclosed in an iron framework must have increased the tendency of the glass to break , for the great conducting power of the iron would render the edges much colder
than the rest of the glass . The journal above alluded to suggests , as preventive of the occurrence of similar accidents , —first , that the framework of all large plate glass windows that are much exposed to the sun should be formed of wood ; and secondly , that the ? painted portion of the Avindow should not be a part of the larger sheet , but