164 



PROCEEDINGS OF THE AMERICAN ACADEMY 



rn. 



67.16 



IV. 



67.13 



These percentages agree closely with those required by the for- 

 mula Cj-Hj^BrgOg, and the behavior of tlie substance is such that it 

 must be considered dibrompyroxanthintetrabromide. It crystallizes in 

 small, brilliant, colorless prisms which belong to the triclinic system. 

 On heating, it is decomposed below 100° with carbonization and the 

 evolution of hydrobromic acid. It is very sparingly soluble in ether 

 or carbonic disulphide ; in boiling benzol or chloroform it dissolves 

 quite freely, and the greater part again separates on cooling. In cold 

 alcohol or glacial acetic acid, it is sparingly soluble ; but, on warming, 

 it dissolves with decomposition and then forms a yellow solution. In 

 the cold, it is unaltered by concentrated sulphuric acid ; on heating, it 

 is carbonized. 



A crystallographic study of the substance gave the following re- 

 sults : — ■ 



CRYSTALLINE FORM OF DIBROMPYROXANTHINTETRABROMIDE. 



Triclinic System. 

 Forms observed, |001} \0U\ {OlT| \UQ\ {{\0\ \J0\\. 



a:b: c= 0.733 : 1 : 2.370. 

 ic = 74° 43'; ac = 83° 40'; ai = 96' 46'. 



filter of Dr. Gooch was used. The great saving of time and labor as well 

 as the increased accuracy attainable by vliis method renders it invaluable in de- 

 terminations of this sort. 



