INTERNAL CAUSES OF VARIATION 



21 1 



MONOBASIC ACIDS OF THE ACETIC SERIES, 



Observe the exceeding complexity of these compounds, and 

 notice that they stand in definite series with uniform differences ; 

 there are no breaks in the series and no missing members until 

 we reach C 21 H 43 . Note too that these compounds may them- 

 selves combine with others ; thus stearin, the characteristic fat 

 of tallow, is C 3 H 5 (C 18 H 35 O 2 ) 3 , in which case 3 H from the acid 

 radical and 3 (HO) from the glycerin radical have united to form 

 3 (H 2 O), or water. 



Above everything else in this series note the wide difference 

 in physical properties arising from a slight difference in chemical 



