174 
from a practical point of view, but is also of great interest 
as being the first recorded instance of the artificial formation 
of a natural colouring matter. The formula to which I was 
led in my examination of the colouring matters of madder, 
viz., C 14 H 10 O 4 , approaches very closely, as Professor Roscoe 
observed, to the one now adopted by Graebe and Lieber- 
mann, C 14 H 8 0 4 . My formula was not founded on theoretical 
views, but simply expressed the composition to which my 
numerous analyses of alizarine and its compounds conducted. 
I have until now seen no reason whatever to adopt any 
other, notwithstanding that Strecker’s formula, C 10 H 6 O 3 has 
been preferred by most chemists, and was even pronounced 
by Laurent to be the only one possible. That my analyses 
do not in the least correspond with the latter formula, but 
are not inconsistent with that of Graebe and Liebermann, 
will be seen by a glance at the following numerical results 
of some analyses of alizarine from various sources : 
I. II. III. IV. V. Mean. 
C 69*15 69-37 69-59 69-66 69-73 69-50 
H 4-04 4-07 4-26 4-00 3*71 4-01 
0 26-81 26-56 26-15 26-34 26-56 26*49 
Of these analyses I. was made with material obtained 
directly from madder, II. and III. with specimens derived 
from rubian by decomposition with acid and with ferment, 
IV. with alizarine from rubianic acid (its glucoside), 
and V. with sublimed alizarine. The three formulse, 
C 14 H 8 0 4 , C 14 H 10 O 4 , and C 10 H 6 O 3 , require the following per- 
centages of C, H, and O : 
C 14 H 8 0 4 . c 14 h 10 o 4 . C 10 H 6 O 3 . 
0 70-00 69-42 68-96 
H 3-33 4-13 3-45 
O.. 26-67 26-45 27-59 
