PROBLEMS OF CHEMISTRY 319 



intelligible in what I still have to say, but I shall try. Thus 

 far, in what has been said about chemical acts, the material 

 side has been kept in view. The relations between the ele- 

 ments; the artificial preparation of the substances that 

 enter into the composition of living things; the changes in 

 the composition of matter at high and at low temperatures ; 

 and, finally, the atom these are the subjects dealt with. 

 But, whenever a chemical act takes place, there are changes 

 in the temperature and in the electrical condition of the 

 substances involved, in addition to the changes in compo- 

 sition. It is while in action that chemical substances are 

 most interesting. Generally we have to content ourselves 

 with observations before and after an act, but we should 

 learn a great deal more about the nature of the act, if we 

 could make observations while it is in progress. We should 

 find it very difficult, if not impossible, to learn the law of 

 falling bodies, if we could only observe bodies before and 

 after they have fallen ; but by observing them in the act of 

 falling we can, without difficulty, deduce the law 



LAWS OF CHEMICAL CHANGE 



Generally speaking, chemical acts are so rapid that it is 

 impossible to make observations during their course. Much 

 progress has been made in this field during the past fifteen 

 or twenty years, and some of the great laws of chemical 

 action have been discovered. What has been learned is, 

 however, only enough to whet the appetite of chemists. 'To 

 illustrate in another way what is meant by making observa- 

 tions during a chemical act, let us take the case of gun- 

 powder. This usually consists of charcoal, sulphur, and 

 saltpeter. A spark is sufficient to cause the chemical act 

 that is accompanied by the explosion. We can collect 

 everything that is formed, and show what changes in com- 

 position have taken place. But we should like to know 

 something about the act itself, and yet, plainly, observa- 

 tions during the act cannot be numerous, or especially in- 

 structive. And so it is with most common chemical changes 



