( 201 ) 



to the method given in R. 20, 223. I will only add that (lie com- 

 plete removal of' nitric acid from the product was effected with 

 particular care as il appeared that this acid is retained with great 

 obstinacy. In order to get the nitration product so pure that it gave, 

 at the ordinary temperature, no, or hut a feeble reaction with 

 sulphuric acid and diphenylamine, it was necessary to wash it many 

 times with cold water and to dry it over lime in vacuo. The organic- 

 acids, which had dissolved in the washings were, of course, recovered 

 in the manner described previously. The removal of the last traces 

 of nitric acid was of great importance in these determinations, because 

 the presence of even very minute quantities of this acid causes, in 

 the analytical method followed here, a too low percentage of the 

 byeproduct. 



In this method about 0.4 gram of nitration mixture is extracted 

 with 100 grams of water and the acidity estimated by titration with 

 "/ 10 alkali. Suppose 1 mgr. of nitric acid (= 0.25°/ ) had been 

 retained in that quantity it is sure to have dissolved together with 

 the whole of the main product. 1 mgr. = 0.016 millimol. 1 cm.' 

 of the alkali corresponds with 0.1 millimol. so that 0.16 cm.' or 

 about 3 drops are required for neutralisation. As the molecular 

 weight of chloronitrobenzoic acid is 201.5 and that of bromonitroben- 

 zoic acid 246, 0.016 millimol. represents, respectively, a weight of 

 3.2 and 3.9 mgr. or of '/ 4 " „ and 1 % of the nitration mixture. 

 The main product contained therein is therefore found too high and 

 the byeproduct correspondingly too low since the latter is found by 

 ditFerence. As the content in byeproduct in these mixtures does not 

 exceed 13% (in the bromo-acids) an error of 'J u / is a rather 

 serious one. 



In order to be able to determine the composition of the nitration 

 mixtures by solubility determinations it was necessary to determine 

 first for the chloro- and bromobenzoic acids, the solubility of the 

 least soluble ones (in both cases the byeproduct) and then the total 

 solubility, when the liquid is kept saturated with this least soluble 

 acid, but mixed with gradually increasing portions of the main 

 product; when the liquid docs not get saturated, all the main product 

 passes into solution. By means of the solubility tables thus obtained 

 the composition of an unknown mixture may be deduced reversedly 

 by determining its solubility figure. 



