i Saligenin 



i Glucose 



i Benzole acid 



CONSTITUENT RESIDUES. 

 C 7 H 8 0, 

 C, H*ol 



27 



1 Populin 



2 Water 



Accordingly, we should not represent populin graphically by 

 three complete circles in apposition, but by the residues of three 

 circles conjoined with one another, as in one or other of these 

 figures : 



Populin 



(26.) The constituent residues existing in salicin and popu- 

 lin form very considerable proportions of the original molecules 

 but in many instances the residues become extremely small. For 

 instance, by combining acetic acid with ammonia we obtain ace- 

 tate of ammonia, a salt produced by the direct union of the two 

 complete molecules, acetic acid and ammonia. Under certain 

 circumstances an atom of water may be eliminated from this 

 acetate of ammonia, whereby it becomes converted into aceta- 

 mide, which by further loss of an atom of water becomes aceto- 

 nitrile, as shown in the following diagrams. 



Thus, in acetamide the residues of acetic acid and ammonia con- 

 stitute but 59 out of 77 parts, while in aceto-nitrile they amount 

 to only 41 parts, or little more than half the weight of the original 

 molecule. Nevertheless, in aceto-nitrile the two small residues 

 stand apart from one another as perfect representatives of, or 

 proxies for, the entire molecules, ready without a moment's no- 

 tice to regenerate them on the concurrence of suitable conditions. 



