CHEMICAL CHANGE AND THE METHODS OF STUDYING IT 21 



the more careful the work and the more delicate the instrument 

 used in weighing, the more nearly do the values approach identity. 

 We are able to state, therefore, that the mass of a system is not 

 affected by any chemical change within the system. 



FIG. 13 



FIG. 14 



This statement simply means that the great law of the conserva- 

 tion of mass holds true in chemistry as it does in physics. Chemi- 

 cal changes, thoroughgoing as they are in respect to all other 

 qualities, do not affect the mass; an element carries with it its 

 weight, entirely unchanged, through the most complicated chemi- 

 cal transformations. 



Superficial observation, as of a growing tree, might seem to give 

 evidence of the very opposite of conservation of matter. But 

 here the carbon dioxide gas in the air, the most important source 

 of nourishment for plants, is overlooked. Similarly, the gradual 

 disappearance of a candle by combustion seems to illustrate the 

 destruction of matter. But if we catch the gases which rise 

 through the flame (Fig. 13), we find that the gases weigh even 

 more than the part of the candle which has been sacrificed in 

 making them. When we take account of the weight of the oxy- 

 gen obtained from the air which sustains the combustion, we find 

 that there is really neither loss nor gain in weight. If we carry 



