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forms is so familiar to those who are much employed in the study 

 or practice of chemistry that the marvel and mystery of it cease 

 to be properly appreciated. There are, I think, two principal 

 ways in which our curiosity is appeased and our feelings of wonder 

 in the presence of natural marvels made to subside. First, there 

 is the legitimate way. An explanation is found for that which at 

 first seemed inexplicable. The curiosity and wonder originally 

 excited are allayed but usually they break out again in connection 

 with some other and profounder problem that comes into view 

 when the first one has been solved. Secondly, there is the illegiti- 

 mate way. In this case no solution is found, but mere familiarity 

 blunts the edge of our curiosity and we cease to wonder at 

 what used to excite our astonishment. Philosophy and science, 

 in so far as it is philosophical, seek to discover the One in the 

 Many and the Unchanging behind the perpetual flux of 

 phenomena. To the chemist, it is the Atom that remains un- 

 changed. The properties of bodies which impress themselves 

 upon us through our senses, belong, not to the atoms as such, 

 but to molecules, which are special collections of atoms, and to 

 larger aggregates built up of molecules. We cannot say, for 

 example, that the atoms of carbon are either black or white ; 

 blackness and opacity belong to the molecules of graphite, but 

 are absent from the diamond, whose molecules are, doubtless, 

 built up of different numbers of atoms differently arranged, 

 although the atoms themselves are the same in each case. The 

 differences between the three forms of the free element carbon 

 may be compared with those between a church, a railway station, 

 and a dwelling-house ; all built of the same kind of bricks and 

 yet profoundly unl'ke. The difference between molecules built 

 up of the same kinds of atoms is, in fact, an architectural 

 difference. 



I must now leave the subject of uncombined carbon and pass 

 to the chemistry of a few of its more important compounds, 

 beginning with those it forms with oxygen. Three of these are 

 known, the three d ! ffering from each other, not only in properties, 

 but also in the ratio of carbon to oxygen. The most important is 

 carbonic acid gas or, in more modern nomenclature, carbon 

 dioxide, almost affectionately known to chemists as CO^ Here 

 one atom of carbon is united to two of oxygen and, as the atomic 

 weights of carbon and oxygen are to each other as 12 is to 16, the 

 proportions by weight are 12 of carbon to 32 of oxygen, or, yet 

 again, 3-nths of carbon and 8-nths of oxygen. Th : s gas is 

 formed, as has already been stated, when any one of the varieties 

 of carbon is burnt in oxygen or in air. It equally results when 

 any substance whatsoever containing carbon is completely burnt. 

 All our ordinary fuels do contain carbon ; peat, wood, charcoal, 

 coal, coke, mineral vegetable and animal oils and fats, alcohol and 

 so on, these all yield carbon dioxide when burnt. Most of these 

 contain hydrogen also, and so the combustion gives rise to water 

 vapour as well, but with this we are not at present concerned. 



