-
Articles/Ads
Article THE CHEMISTRY OF COMMON THINGS, ← Page 3 of 5 →
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things,
hot to burn these , gases ,. or combine them with the oxygen of the air , and they consequently rise in a column of smoke , which is soon afterwards burnt by the yhite heat of the flame itself which is , therefore , kept up by a succession of decompositions and compositions , and is in fact a slow explosion . ,
Observe the different degrees of heat required to effect the successive changes in the state and constitution of the substance of the candle . A heat considerably Below that of red-hot iron is sufficient for its liquefaction . The wlxole of the surface of the candle round the wick is in a state of fusion ,. except the edge , which is solidified by
the cold external ai ^ j and this : solid edge forms a wall , which prevents the liquid matter inside from running down the sides of the candle , Wh , en , tbybeing carried about , or otherwise , the flame is thrown against this wall so as to melt it down , the fluid wax or tallow runs over * an 4 the candle " gutters . "
, But it will require a full red heat to decompose this fluid matter , and separate it into its constituent gases , hydrogen and carbon ; and even this is not sufficient to combine these gases with the oxygen of the air . If , for instance , a piece of wax be dropped , on a surface of red-hot iron , it will melt and be decomposed , the gases rising in the form of smoke , which will not , however , take fire , as the heat of the iron is not sufficient for that ; but if a piece of lighted paper be applied to this smoke , it will inflame , and burn .
When the flame is blown out , or extinguished , the red spot on the wick remains . This continues for some time to decompose the liquid matter which rises to it , and the smoke ascends as before , but does not burn . If a light be applied to , this smoke , at a distance of some inches above the wick , small portions of the wick will successively takofire , and a flame will be seen to pass downwards from the light to the wick , and re-light the candle . This phenomenon has been
compared to a flash of lightning travelling at a slow rate . It is evident , that when the mixed gases issue from the wick , only those portions which are in connection with the atmosphere can be combined with it , and so produce flame . Hence it might be expected that the flame would be of a globular form , hollow in the middle , and filled with unburnt gas ; and it would take this form , if the pressure of the atmosphere were the same upon all sides of it . But since heated air is much rarer and more attenuated than air at the usual
temperature , its weight is inconsiderable compared with that of cold air , and it rises , being forced up , by the superior pressure of the latter . So , the air immediatelv above tlie flame , ascends together with the wlucfi result from the qombustion—being highly heated- —and gases tlie top of the flame is consequently relieved from pressure . This
explains the peculiar , form taken by the flame ; the pressure being greatest at the bottom , and decreasing gradually to tlie top , tlie flame cuds iu a point . It still , however , remains hollow , the vacant ^ pace being the dark spot seen in the middle , which takes a form some what similar to that of the flame itself . To prove this , take a shp of paper , hold it in the flame a little over the wick for a few
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
The Chemistry Of Common Things,
hot to burn these , gases ,. or combine them with the oxygen of the air , and they consequently rise in a column of smoke , which is soon afterwards burnt by the yhite heat of the flame itself which is , therefore , kept up by a succession of decompositions and compositions , and is in fact a slow explosion . ,
Observe the different degrees of heat required to effect the successive changes in the state and constitution of the substance of the candle . A heat considerably Below that of red-hot iron is sufficient for its liquefaction . The wlxole of the surface of the candle round the wick is in a state of fusion ,. except the edge , which is solidified by
the cold external ai ^ j and this : solid edge forms a wall , which prevents the liquid matter inside from running down the sides of the candle , Wh , en , tbybeing carried about , or otherwise , the flame is thrown against this wall so as to melt it down , the fluid wax or tallow runs over * an 4 the candle " gutters . "
, But it will require a full red heat to decompose this fluid matter , and separate it into its constituent gases , hydrogen and carbon ; and even this is not sufficient to combine these gases with the oxygen of the air . If , for instance , a piece of wax be dropped , on a surface of red-hot iron , it will melt and be decomposed , the gases rising in the form of smoke , which will not , however , take fire , as the heat of the iron is not sufficient for that ; but if a piece of lighted paper be applied to this smoke , it will inflame , and burn .
When the flame is blown out , or extinguished , the red spot on the wick remains . This continues for some time to decompose the liquid matter which rises to it , and the smoke ascends as before , but does not burn . If a light be applied to , this smoke , at a distance of some inches above the wick , small portions of the wick will successively takofire , and a flame will be seen to pass downwards from the light to the wick , and re-light the candle . This phenomenon has been
compared to a flash of lightning travelling at a slow rate . It is evident , that when the mixed gases issue from the wick , only those portions which are in connection with the atmosphere can be combined with it , and so produce flame . Hence it might be expected that the flame would be of a globular form , hollow in the middle , and filled with unburnt gas ; and it would take this form , if the pressure of the atmosphere were the same upon all sides of it . But since heated air is much rarer and more attenuated than air at the usual
temperature , its weight is inconsiderable compared with that of cold air , and it rises , being forced up , by the superior pressure of the latter . So , the air immediatelv above tlie flame , ascends together with the wlucfi result from the qombustion—being highly heated- —and gases tlie top of the flame is consequently relieved from pressure . This
explains the peculiar , form taken by the flame ; the pressure being greatest at the bottom , and decreasing gradually to tlie top , tlie flame cuds iu a point . It still , however , remains hollow , the vacant ^ pace being the dark spot seen in the middle , which takes a form some what similar to that of the flame itself . To prove this , take a shp of paper , hold it in the flame a little over the wick for a few