166 PROCEEDINGS OF THE AMERICAN ACADEMY 



I. 0.3816 grm. substance gave 0.6333 grm. CO, and 0.0918 gnu, 



HA 

 II. 0.3137 grm. substance gave 0.2978 grm. AgBr. 

 III. 0.2577 grm. substance gave 0.2419 grm. AgBr. 



Calculated for CijHioBrjOj. Found. 



I. II. m. 



C 44.22 45.25 



H 2.51 2.67 



Br 40.20 40.40 39.94 



The analyses showed that the substance was dibrompyroxanthin, 

 and that it was formed from the bromine derivative already described 

 by the subtraction of bromine. 



In hot alcohol it dissolves readily, although in cold it is sparingly 

 soluble. It is quite soluble in ether or carbonic disulphide, and very 

 readily in benzol, chloroform, or glacial acetic acid. 



From a solution in warm chloroform, it crystallizes in large, compact, 

 twinned forms of the monoclinic system, which are dichroic. In con- 

 centrated sulphuric acid, it dissolves with an intense, pure blue color. 

 This blue solution, on dilution with water, throws down a yellow pre- 

 cipitate, which is apparently the unchanged substance. If quickly 

 heated upon platinum foil, it melts to a perfectly clear yellow liquid ; 

 but it is impossible to determine its melting point, since it decomposes 

 and carbonizes when its temperature is more gradually raised. A 

 solution in carbonic disulphide, when mixed with bromine, gradually 

 deposits well-formed crystals of the tetrabromide. This simple sub- 

 stitution product I have not succeeded in making directly from 

 pyroxanthin. In every case where a smaller quantity of bromine 

 was employed, the addition product was still formed, and a part of the 

 pyroxanthin remained unaltered. 



I have also studied the action of aqueous bromine, but have not 

 been successful in obtaining any definite products. If pyroxanthin is 

 suspended in water, and bromine gradually added, or the vapors of 

 bromine carried in by a current of air, a white amorphous substanceis 

 slowly formed, which is almost insoluble in water, but extremely solu- 

 ble in other ordinary solvents. By evaporation of such solutions, the 

 substance again separates in an amorphous condition. In alkalies it 

 dissolves, forming a deep-brown solution, from wliich nothing can be 

 precipitated by the addition of acids. 



Since there appeared to be little hope of effecting its purification by 

 ordinary methods, I proceeded to analyze carefully prepared material. 



