NEW CONCEPTIONS IN SCIENCE 



weight, in combining powers, in every sort of way. 

 Some seem to have three, four, and five arms with 

 which to hold other atoms, while some have but 

 two, some one, and some none at all. 



Moreover, the chemist makes a distinction be- 

 tween the atom, that which is irreducible, and the 

 molecule, which may contain two or two hundred or 

 two thousand atoms. And by methods of exceed- 

 ing refinement he will fix this number for each mole- 

 cule. For water there will be three, for salt two, 

 for sulphuric acid seven, for sugar forty-five, and 

 so on. The molecules of water, salt, acid, sugar, are 

 the ultimate particles of their substances; divide 

 them further, and they cease to be water, salt, etc. 

 They are resolved into their primitive atoms. 



By a very simple experiment the chemist shows 

 that, at ordinary temperatures, molecules usually 

 contain at least two atoms. Here are two bulbs 

 containing two different gases, say, hydrogen and 

 chlorine. Mix them and explode them, and the re- 

 sultant gas occupies the same space as did the two 

 before. But the result is no longer a simple sub- 

 stance, but a compound hydrochloric acid in the 

 state of a gas. Following Avogadro's hypothesis, 

 it is supposed that equal volumes of all gases, 

 at equal temperature and pressure, contain the 

 same number of molecules. The chemist reasons, 

 therefore, that the molecules of the hydrogen and 



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