2io CAUSES OF VARIATION 



Something over eighty distinct kinds of matter are known ; 

 therefore some eighty kinds of atoms are assumed, and this ex- 

 hausts the possibilities so far as unlike like atoms are concerned 

 (unless other atoms are subsequently discovered or created). 



But this does not exhaust the possibilities of matter, for these 

 atoms combine together, forming new units (called molecules) 

 with distinct properties. Thus NaCl (sodium chlorid) is differ- 

 ent in every way from either the sodium or the chlorin atoms 

 that have united to produce it. In this way these (eighty) 

 various atoms effect all sorts of combinations, many of them 

 exceedingly complex, 1 each constituting a new material unit, a 

 sufficiently large number of which constitutes a measurable 

 quantity of a substance whose real composition could rarely be 

 predicted by any of its visible properties. The following table 

 of chemical formulae is presented for two purposes : (i) to show 

 the exceeding complexity of ordinary materials ; (2) to show how 

 certain groups of atoms (as CH 2 or CO 2 H) 2 behave as units, 

 effecting profound changes in the properties of their compounds. 

 It is evident that the possible combinations, even with the few 

 most common atoms, as C, H, O, N, Fe, Na, K, P, S, are 

 practically infinite when they are able to organize themselves 

 into larger units, giving rise to complex series like the table on 

 the following page. 3 



In this table the radical CO 2 H runs through the entire series, 

 giving a kind of genetic quality to the compounds, while specific 

 differences accompany the varying numbers of C and H atoms 

 present with the radical. It is to be noted, however, that these 

 C and H atoms are in definite proportion to each other, namely, 

 C n H 2n+1 ; that is, for every atom of C there will be one more than 

 twice as many atoms of H, + CO 2 H, all of which is extremely 

 suggestive as early steps in the world of organized matter. 



1 The composition of strychnine, C2iH 2 2N 2 O 2 , and that of grape sugar, 

 Ci2H 2 2On, are both exceedingly simple as compared with many known sub- 

 stances. 



2 Such groups of atoms that move together are known as "radicals." They 

 are in every sense units and are capable of replacing or of displacing other atoms 

 in their constructions. 



8 We are told by the chemists that more than one hundred thousand separate 

 compounds are now known. 



