CONSTITUENTS OF AIR. 



the large and sudden evolution of heat and light arising from 

 the combination of a class of bodies, called combustibles, with 

 oxygen. 



If a piece of charcoal be heated to redness, it will immediately 

 begin to combine chemically with the oxygen of the atmosphere. 

 A great heat and a vivid light are produced in this combination, 

 and the product of it is a compound gas, composed of oxygen and 

 carbon, and called carbonic acid. 



In like manner, if sulphur or phosphorus be similarly heated, 

 similar effects will ensue. 



But since it is evident that these phenomena thus produced in 

 common air arise exclusively from the presence of oxygen, which 

 nevertheless forms only a fifth part of that air, it may naturally be 

 inferred that if the same combustibles were placed in an atmo- 

 sphere containing a greater portion of oxygen, and still more if 

 they were placed in an atmosphere of pure oxygen, the phenomena 

 would be far more vivid. 



And this is accordingly found to be the case. 



All substances, which are capable of burning in common air, 

 burn with far greater intensity and splendour in an atmosphere of 

 pure oxygen. A piece of wood on which the least spark of light 

 is visible, which would be spontaneously extinguished in common 

 air, will burst into flame the moment it is plunged in a jar of 

 pure oxygen. A piece of charcoal, heated to redness at its point, 

 will in like circumstances enter into vivid combustion, emitting 

 the most brilliant scintillations, until it altogether disappears. 

 Phosphorus similarly treated burns with a light too splendid 

 to be looked at without pain. If the extremity of a coil of steel 

 wire be heated to redness, and plunged in such a jar, the wire 

 will be rapidly burnt, emitting in like manner streams of brilliant 



These substances severally disappear in the process of combus- 

 tion, and before science had attained to its present state of advance- 

 ment it was supposed that they were destroyed. It is now 

 known that the destruction of matter, in any form, and by any 

 natural process, is as impossible as its creation. It is a physical 

 maxim of high generality and undoubted truth that nothing but 

 the immediate operation of the Divine will can either augment or 

 diminish the quantity of matter composing the world. Whenever 

 ponderable matter, therefore, seems to disappear, we are called 

 upon to trace it, to discover its hiding-place, and to explain the 

 nature and the cause of the change which produces its disappear- 

 ance. In the present case nothing is easier. 



23. Let us suppose, for example, that a piece of lighted charcoal 

 of sufficient magnitude is plunged in a closed glass jar filled with 



11 



