152 



Dr. Stenhouse on Rubia munjista. 



[1864. 



in alcohol containing potassa show three bands of absorption just alike in 

 appearance. By measurement it seemed probable that the bromine sub- 

 stance gave the bands a little nearer to the red end ; but the difference, if 

 real, was very minute. The fluorescent light of the ethereal solution was, 

 I think, a trifle yellower in the bromine substance, that of alizarine being 

 more orange.*' 



The following are the results of the ultimate analysis of the brominated 

 alzarine dried at 100° C. :— 



I. '375 grm. of substance gave '207 grm. bromide of silver. 



II. *703 grm. of substance gave '389 grm. bromide of silver. 



III. -401 grm. of substance gave '221 grm. bromide of silver. 



IV. '543 grm. of substance gave '300 grm. bromide of silver. 



V. '3575 grm. of substance gave "695 grm. of carbonic acid and '0760 

 grm. of water. 



VI. '454 grm. of substance gave '8790 grm, of carbonic acid and '0965 

 grm. of water. 







Theoiy. 



I. 



11. 



III. 



IV. 



v; 



VL 



^60 



= 360 



52-94 











53-03 



52-81 





= 16 



2-35 











2-36 



2-36 



Br, 



= 160 



23-53 



23-49 



23-54 



23-45 



23-51 





• • . r 





= 144 



21-18 

















680 



100-00 















From this somewhat anomalous formula. 



Ceo H,e Br, 0,3= H, O^, 2(0,^ H, BrOe), 

 I was for some time inclined to think that it might be a mixture of bromi- 

 nated alizarine with free alizarine ; but as all the six samples analyzed were 

 prepared at different times, it is highly improbable that such uniform analy- 

 tical results could be obtained if they were from a mere admixture of sub- 

 stances. The existence of a brominated compound is also cojifirmed 

 by its dyeing properties, which differ so remarkably from those of 

 alizarine. 



Action of Bromine on Purpurine. 



"When pure purpurine is dissolved in spirit mixed with a considerable 

 quantity of water, and an aqueous solution of bromine added, as in the 

 case of alizarine, a yellow amorphous precipitate is produced. The solution 

 separated from this by filtration, when heated to expel the spirit, gives no 

 j^reci'^itate whilst hot ; but on cooling, a very small quantity of a brown 

 resinous powder is deposited. From this it is evident that the presence of 

 a small quantity of purpurine in alizarine will not interfere with the pro- 

 duction of pure brominated alizarine, if the precaution be taken to collect it 

 from the solution whilst it is still hot. 



I think it right to state that the experiments and analyses detailed m the 

 preceding paper have been performed by my assistant, Mr. Charles 

 Edward Groves. I cannot conclude this paper without again acknowledg- 

 ing the essential services I have received from Professor Stokes, who kindly 

 submitted the different products obtained by me to optical examination. 



