On the Glassification of Carbon- Compounds. 315 
hydroxy groups connected with the same carbon atom, upon de¬ 
hydration yield compounds characterixed by the group 
R'—C^q_ h , the carboxyl or acid group. It is also evident 
why aldehydes and not ketones yield acids upon oxidation. 
The table also shows that there are compounds of a mixed or 
double character, such as hydroxy- or keto-aeids, alcohol- 
aldehydes, etc. 
Once having demonstrated the common origin of these com¬ 
pounds, the enumeration of which would be'merely a matter of 
time-, and having shown their general relationship, it is much 
easier later in a course of instruction, when it becomes neces¬ 
sary to treat of alcohols, aldehydes, acids, etc., as classes of 
compounds, to give a comprehensive rather than a disconnected 
view of the entire subject. If the student once grasps the idea 
that alcohols, aldehydes and acids are families of the same 
tribe the point gained can hardly be overestimated. The 
student is otherwise apt to regard alcohols and acids, e. g. in 
the formation of esters, as two rather antagonistic classes of 
substances, as the alchemists considered inorganic bases and 
acids, a fantastic notion from which even modern chemistry has 
not completely freed itself. It appears natural to the average 
student that the hydroxy-hydrogen of the acid or carboxyl 
group should be replacable by a metal to form 
e. g. sodium acetate, CH 3 C^Q_^ a , but that the hydroxy- 
hydrogen of an alcohol group, or even the hydrogen of a 
methylene group e. g. in R'.CH 2 . R', should also be replacable 
by sodium, is something that usually appears contradictory to 
his notions of bases, acids and salts. However, if the genetic 
relations of such compounds has been demonstrated, such false 
notions will be dispelled. It can also be easily explained to 
him why in one case the hydrogen should be somewhat more 
readily replacable by sodium than in another, viz., because of 
its somewhat modified surroundings. 
It may be worth mentioning that the sulph-hydrides or 
mercaptans, the sulphides, the thio-aldehydes, thio-acids, etc., 
can be deduced and classified in the same way by replacing the 
