2ir> 



philo-nphers. Now. an atom i- regarded ratlier a- an isolate or 

 which i> indivisible by physical :v - and chemical forces, \\-hilst the atom 

 of the ancients \\as mechanically and uvometricallv indi\ i-iMe. \\ hen 

 I 'alt on ( 1 v| ' 1 ) discovered t he la w of mult iple propoi t ions, he pronounced 

 himself in favour of the atomic doctrine, because it enables this law to 

 Ke very easily understood. If the divisibility of everv element has a 

 limit, namely the atom, then the atoms ot element- are the extreme 

 limits of all di visibilit v. and t hey ditl'er from each other in t heir nat ure, 

 and the tormation ot a compound trom elementary matter must consist 

 in the a-'uTe-'at ion of several different atoms into one whole or system 

 of atoms, now termed mi.rti 1 '?''* or ///'-/<*///,>. As atoms can onlv com- 

 bine in their entire masses, n i- evident that not onlv the law of defi- 

 nite coi M posit ion. but a 1 so i hat of multiple proport ions, must apply to the 

 combination of atoms with one another ; for one atom of a substance 

 can combine with one. two. or three atoms of another substance, or in 

 iM'iier;i 1 one. t wo. i h ive atoms ( if one siib-t anee are able t < combine with 

 one. t wo. or t hive atoms of a not her : this b 'inu' the essence of the law 

 of multiple proportions. Chemical and physical data are verv well 

 explained by the aid of the atomic theory. The displacement ot one 

 element by another follows the law of equivalency. In this case one 

 or several atom- of a Lnven element take the p'ace < if one or several 

 a t oms ot another element in its compounds. I he at on is of di lie rent 

 -ubstances can lie mixed together in the same sense a- sand can be 

 1 1 1 1 xed v. 1 1 1 1 da v. "I I ie\- do not unite i n' o one \\ hole /.<.. t here is not a 

 perfect blendiiiLf in the one or other case, but only a juxtaposition, a 

 homogeneous whole beinu' formt d from individual parts. This is 

 the tir-t and mo.-i simple form of applying the atomic theory to the 

 explanation of chemical phenomena.' 1 '* 



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