436 DRIED JUICES 



Chemical Reactions. (a) General Reactions. The following are 

 the most important general reactions for aloes : 



Schonteteri's Reaction. Dissolve 0-1 gramme of aloes in 10 c.c. of 

 boiling water and add 0-5 gramme of powdered borax ; a green fluor- 

 escence is produced. This reaction is due to barbaloin ; all aloes except 

 Natal (see below) respond to it. 



Borntrager's Reaction. Dissolve 0-1 gramme of aloes in boiling 

 water, cool, add 10 c.c. of benzene, shake vigorously, separate the 

 benzene solution and shake it with solution of ammonia ; the alkaline 

 solution is coloured red. This reaction is due to aloe-emodin ; all 

 aloes except Natal, respond to it. 



Chrysammic Acid Reaction. Heat 1-0 gramme of aloes with 20 c.c. 

 of nitric acid in a dish on a waterbath for 2 hours replacing the 

 liquid lost by evaporation ; then dry on the waterbath ; the resulting 

 brown powder dissolves in ammoniacal water with violet coloration. 



(6) Special Reactions : 



Natal Aloes, which is quite distinct from all other aloes, is readily 

 identified by Histed's reaction : Dissolve 0-1 gramme of aloes in a 

 few drops of sulphuric acid on a porcelain slab and gently blow the 

 vapour of fuming nitric acid over the surface ; a green, then red, and 

 finally deep blue colour is developed. 



Curagao Aloes. To 10 c.c. of a freshly prepared, 0-1 per cent, aqueous 

 solution of the aloes add 1 drop of a 5 per cent, solution of copper 

 sulphate, a trace of sodium chloride and a few drops of alcohol ; 

 a fine wine-red colour permanent for 24 hours is produced. Of the other 

 varieties of aloes, Cape aloes alone may give a pale colour which, 

 however, rapidly fades. The reaction is due to isobarbaloin (see below). 



Cape Aloes. Drop a few drops of nitric acid on a little of the crushed 

 aloes ; a permanent green colour is gradually produced. 



Socotrine and Zanzibar Aloes. With the nitric acid test, a reddish 

 brown colour is produced. Under the same conditions Curayao aloes 

 gives a crimson colour. 



Constituents. The principal constituent of all the foregoing varieties 

 of aloes (with the exception of Natal aloes) is the pale yellow, crystalline, 

 glucoside, barbaloin (formerly called socaloin, zanaloin, capaloin, &c., 

 according to its origin). In Cura9ao and in true Barbados aloes the 

 barbaloin is accompanied- by isobarbaloin which is crystalline and 

 isomeric with barbaloin but easily distinguished from barbaloin, as 

 it yields the cupraloin test (see above). Socotrine and Zanzibar aloes 

 contain no isobarbaloin, and Cape aloes traces only. 



The crystalline aloin is accompanied by an amorphous aloin, 

 /?-barbaloin, which may be produced by heating barbaloin for about 

 three hours to 160-165 ; it is isomeric with barbaloin, and con- 

 stitutes part at least of the water-soluble substances other than 



