474 LILIACEM 



9 



When bromine water was added in excess to an aqueous 

 solution of the aloin, a copious yellow precipitate fell. This was 

 collected after having been in contact with excess of bromine 

 water for an hour, washed, dried, and crystallized three times 

 from spirit. The brominated aloin was in beautiful yellow 

 crystals, which were rather soluble in cold alcohol, and were 

 somewhat more stable than the aloin itself. It retained only a 

 trace of water when dried in a yacuum over sulphuric acid, 

 which was given off on heating to 100^ C. to 1 W C. -2526 

 gram of the perfectly dry substance gave '2539 gram of silver 

 bromide, corresponding to 42*75 per cent, of bromine. 



In 1875, Dr. Tilden proposed, as the result of the consider- 

 ation of a number of analyses of aloins and their derivatives 

 made by himself and others, that the aloins obtained from Bar- 

 badoes and Zanzibar aloes might be considered isomeric bodies, 

 with the empirical formula C^^H'^0^, which also agrees closely 

 with his analysis of nataloin* This formula requires 59'6 

 per cent, of carbon and 5 '59 per cent, of hydrogen. Its 

 tribromo-derivative requires 42'93 per cent, of bromine. 



It will be seen that of the numbers obtained in Mr- Shen- 

 stone's analysis, those for the hydrogen and bromine agree very 

 closely with these, and that the proportion of carbon, though a 

 little high, also agrees fairly welL 



The water of crystallization found, 16 per cent., is rather 

 more than the amount which would correspond to three mole- 

 cules, ix.9 14*3 per cent. The difficulty of getting air-dried aloin 

 of constant composition, however, is so great that the result is 

 not of much value. 



The following comparative observations with Jafarabad aloin 

 and Br, Tilden's zanaloin were made: 



There is no distinguivshable difference in the crystalKne form 

 of the two aloins. 



Ts either of them gives any change of colour in the cold when 

 moistened with ordinary strong nitric acid ; both of them are 

 reddened by fuming nitric acid. And the Jafarabad aloin, by 



