1028 
For all compounds C,H,ARC with repetitions this gives a total of 
42 + 1092 + 3640 = 4774 cases. *) , 
If now we inquire how many of these theoretically possible iso- 
merides have been tested as to the replacement of their substituents 
we get the following information : 
Of the 315 possible isomerides C,H, AB (incl. A= B) 130 have 
been tested as to substitution and the results are distributed over 
214 papers. 
For the 4774 possible isomerides C,H,ABC (incl. A,B and A,) these 
figures are: of 232 compounds the substitution has been described 
in 360 papers. 
This shows that only a very small portion of the possible com- 
pounds C,H,AB and C,H,ABC has been tested as to the replacement 
of their substituents ; it only amounts to fully 7 °/,. 
Hence, it is hardly to be expected that from this general conclu- 
sions might be drawn even if all published cases of substitution were 
suitable for the object in view. But this is by no means the case. 
After a careful study of the above named 214 + 360 — 574 articles 
we even arrive at the disappointing result that this vast material is 
almost valueless for a closer study of the substitution. For in such 
a study we not only want to know in what particular combinations 
substitution ean occur, but also how this takes place under the same 
conditions. For only then will it be possible to compare mutually 
the substitution in the different groups and thus obtain a better 
insight by investigating this problem. And exactly in this regard, 
the material at disposal almost entirely forsakes us. 
The reason is obvious. The experiments on substitution carried 
out up to the present have always been executed with quite a 
different purpose and were not intended for a systematic study of 
this problem. Hence, the work was conducted hardly ever under 
comparable conditions. The only results obtained up to the present 
is that we know that in a comparatively limited number of cases 
substitution is possible. From this we may predict with great pro- 
bability that there is a possibility of substitution in a number of 
other cases. If, for instance we know that in chloronitrobenzenes 
with one or several chlorine atoms or nitro-groups the chlorine is 
mobile, it is to be considered as very probable that this will also 
be the case with the other halogen-nitrobenzenes of the same 
structure. 
1) Our fellow member Hk. Dr Vries was kind enough to furnish me with the 
formulae used here. 
