It should be borne in mind, as incidentally referred to on page 811, that the possibilities which the constructive processes of organic chemistry open to us are almost beyond limit. Not a few of those products which we have solely heretofore, and do mostly even now, depend upon crude vegetable drugs for their origin, are at the present time being built up synthetically to such perfection as often to challenge recognition of distinctive sources. Of these, the Pharmacopoeia would recognize more than it does were it not for partial secrecy in working formula and manufacture. Quite a number are employed so universally that the present day text-book excluding them might be considered more or less incomplete. In order that the chemical relationship may be better understood they have been treated, so far as practicable, in the same ordered sequence as adopted in Part IV. Before taking them up individually, it may be well to show, by graphic formulas, the facility with which the construction and substitution of one atom or a group of atoms for others may be effected - a process which invariably results in giving each time a different substance. In order to do this, and to carry along direct relationship, some of the compounds previously treated will have to be introduced at the sacrifice of repetition, but this may be considered not in the least a disadvantage to the student.
Phenol (Carbolic Acid)= C6H5OH
Toluene, Methyl-benzene== C6H5.CH3
Xylene, Dimethyl-benzene= C6H4(CH3)2
Phenol or Carbolic Acid= C6H5OH
Benzaldehyde, Oil of Bitter Almond-C6H5.COH