( 524 ) 
MESSsINGER-FRITSCH!) moist combustion process so as to make more 
sure about the true percentage of carbon. We first tested the accuracy 
of the process by some blank experiments and some combustions 
of salicylamide. 
V. 0.1371 gram of indican (Indigofera) heated with sulphuric 
acid and potasium dichromate yielded 0.2341 gram of carbon dioxide 
= 56.5 percent of carbon. 
VI. 0.2169 gram of indican (Polygonum) yielded 0.4517 gram of 
carbon dioxide = 56.8 percent of carbon. 
If we now take take the mean of these two determinations the 
composition of indican is: 
56.7 pCt. C 
5.8 pCt. H 
4,7 pCt. N 
which satisfactorily agrees with that calculated from MARCHLEWSKI’s 
formula. 
For the determination of the molecular weight the cryoscopic 
method was used, as indican is too little soluble in the liquids 
generally used in the process based on the increase of the boiling 
point. 
Two determinations were made: 
I. 0.1935 gram of indican (Polygonum) dissolved in 24.89 gram 
of water lowered the freezing point to the extent of 0.058°. 
Il. 0.8301 gram of indican dissolved in 24.89 gram of water 
lowered the freezing point to the extent of 0.208°. 
From these determinations the following figures are calculated for 
the molecular weight: 
I 248 en II 297 
which shows that it is not a multiple of 295. Ci: Hi; NO; must be 
accepted as the molecular formula of indican. 
The determinations of the water of crystallization were done with 
indican from Polygonum. 
I. 0.4149 gram of indican lost on drying in vacuo 0.0594 gram 
of water. 
IJ. 3.2262 gram lost 0.4943 gram. 
III. 0.2291 gram of the dried indican when exposed to the air 
until the weight was constant, absorbed 0.0393 gram of water °). 
1) Lieb. Ann. 294, p. 79. 
*) The amount of water which is reabsorbed depends on the state of humidity of 
the air. 
