NEW CONCEPTIONS IN SCIENCE 



strictly true, it would, of course, explain very 

 simply why one substance is able to displace an- 

 other in a given compound ; in the language of the 

 older chemistry, why, for example, the metals have 

 a greater "affinity" for chlorine than for bromine. 

 A long list of combinations might be compiled 

 which strictly follows this law. Unfortunately, an- 

 other list might be made of those which seem ex- 

 ceptions, and M. Berthelot's celebrated "principle 

 of maximum work" seems to be exact only at abso- 

 lute zero. It is an ideal rather than an actual law. 

 Closely connected with these questions, as M. 

 Berthelot has shown, is the curious problem of the 

 allotropes. Red phosphorus and white phospho- 

 rus are both "elements," and the same element 

 at that. One is a poison, the other harmless ; one 

 may be changed into the other merely by heat- 

 ing. One kind of sulphur forms crystals, another 

 will not ; a third forms a different kind of crystals. 

 Here, again, heat will effect a transformation. Ozone 

 and common oxygen smell and act differently, yet 

 an electric current of high tension will convert the 

 one into the other. Charcoal, graphite, and the 

 diamond are all forms of the same element, carbon. 

 Here was one of the paradoxes of chemical philos- 

 ophy. It was not easy to see how an element, 

 supposed irreducible, indestructible, and unchange- 

 able, could exist in more than one guise. 



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