316 MODERN SCIENCE READER 



us in speaking with confidence about it. Countless experi- 

 ments yet unborn will have to be tried. In thinking of the 

 possibilities, we are confronted with what appears to be a 

 paradox. It has been pointed out that high temperature, 

 in many cases, has the effect of decomposing substances. 

 This shows that these substances are more stable at low 

 temperatures than at the ordinary temperatures. In other 

 words, if heat causes the constituents to separate, cold 

 might apparently cause them to unite more firmly. But, 

 if this is so, why do not substances act upon each other 

 readily at low temperatures? It may be that the constit- 

 uents are so firmly held together that they cannot move 

 about among one another, as they must in order to combine. 

 The water that is frozen in a glacier does not act like water 

 at ordinary temperatures. It is, as it were, chained up 

 and prevented from obeying the laws of water. 



THE GREAT UNSOLVED 



In what I have thus far had to say, I have kept in view 

 certain problems which do not necessarily call for much 

 speculation. It would, however, hardly be fair to leave 

 the speculative side of chemistry entirely out of considera- 

 tion. Sometimes young pupils are introduced to chemistry 

 through the atom. Only very young, or very ignorant, 

 persons can talk with confidence about atoms. The further 

 one goes into the mysteries of chemistry, the more myster- 

 ious appears the atom. In fact, the atom is the great un- 

 solved problem of chemistry. But this is subtle. What is 

 an atom ? Ah ! that is the question. It has been a favorite 

 subject of thought from the earliest days. Up to the begin- 

 ning of the ninteenth century, however, it was nothing but 

 a metaphysical plaything. The wits of generations of phil- 

 osophers have -been sharpened by efforts to decide whether 

 matter is infinitely divisible or not. Take a piece of, say, 

 iron. No matter what its size may be, it can be broken up 

 into smaller pieces; and each of the pieces thus obtained 

 can be still further subdivided. Now, how far can this 



