324 Krenters—On the Classification of Cartoon-Compounds. 
then, the raison d’ etre for the one or the other is looked for it 
fails to become apparent. If the periodic system is what 
Richter states it to be: if it not only places the elements and 
their derivatives in such position to point out their relations, 
but for this very reason may also serve as a basis for classifi¬ 
cation of chemical compounds for didactic purposes, why should 
it not be made serviceable in the study of carbon compounds as 
well as in the study of all other compounds? 
The hydro-carbons are almost universally made the basis of 
study of the carbon compounds. A classification of them, there¬ 
fore, becomes of fundamental importance. The best standard 
of classification seems to be that of the degree of saturation as 
expressed by the following formulas of saturation: C n H 2n -f- 2 , 
C n H 2n , C n H 2n- 25 C n H 2n-4> C n H 2n _ 6 , etc. Each formula of satu¬ 
ration comprises one, several or even many series of hydro¬ 
carbons, which can be classified secondarily according to their 
non-cyclic or cyclic character. The classification of the hydro¬ 
carbons being accomplished satisfactorily, one of the principal 
difficulties of a comprehensive study of the carbon compounds is 
overcome. The order in which the derivatives of these hydro¬ 
carbons are to be considered is next in importance, and here, 
as well as in the fundamental classification of the hydrocarbons, 
writers on chemistry, as we have already seen, generally 
differ. 
Those who follow the periodic system in general will e. g. 
upon reaching the fifth group, after a discussion of the elements 
nitrogen, phosphorus, arsenic, antimony and bismuth, take up 
their hydrogen derivatives, then their halogen derivatives, then 
their oxygen, sulphur, etc., derivatives, following the order in 
which these elements are generally studied, viz. : hydrogen, the 
halogens, the oxygen group (O, S, Se, Te), the nitrogen group 
(N, P, As, feb, Bi). Why the same order should not be followed 
in the study of carbon-compounds it is difficult to understand. 
True it is that it is partially followed, but never consistently, 
at least not in the text or reference books. 
If such a system of classification is carried to its logical con¬ 
clusion it evidently leads to a study of nitrogen derivatives in 
