OF ARTS AND SCIENCES. ' 253 



XIII. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A NEW METHOD FOR THE QUANTITATIVE 

 DETERMINATION OF HYDROXYL. 



By C. Loring Jackson and G. W. Rolfe. 



The methods now in use for determining the number of hydroxyl 

 radicals in a molecule can be divided into two classes, — those which 

 consist in the analysis of the acetyl or benzoyl compound, and those 

 which depend on the saponification of the acetyl compound and the 

 quantitative determination of one or other of the products of the de- 

 composition. Methods of the first class cannot be applied to sub- 

 stances having large molecular weights, as then the differences in 

 percentage composition approach the limit of error of the analysis ; 

 and even methods of the second sort have led to false conclusions in 

 many cases, (for instance, with assculine and sesculetine, which give 

 soluble compounds with magnesic hydrate,) or are inapplicable, owing 

 to the instability of the compound with saponifying agents. We have 

 worked out, therefore, a new method for determining hydroxyl quan- 

 titatively, which is applicable in cases where the methods now in use 

 can be applied only with difficulty or give uncertain results, and, we 

 hope, will commend itself also in other cases on account of its simpli- 

 city, as it does away with the additional operation of saponification — 

 often a tedious one — necessary in methods of the second class. 



Our process consists in converting the substance into its parabrom- 

 benzoyl compound, and determining the amount of bromine introduced 

 by an analysis according to the method of Carius. It therefore belongs 

 with methods of the first class, but has the advantage that the differ- 

 ences in percentage composition are larger than when carbon and 

 hydrogen are determined in the benzoyl or acetyl compounds, as is 

 shown by the following comparison of the differences caused by the 

 presence of one more hydroxy] in the molecule between the percent- 

 ages of carbon in the benzoyl and of bromine in the brombenzoyl 



