ALOE. 687 



half its weight of aloes, forming an acid liquid which exhibits similar 

 reactions. The solution of aloes in potash or ammonia is precipitated 

 by acids, but not by water. 



The most interesting constituents of aloes are the substances known 

 as Alo'in. This name was originally applied to an aloin which, as it 

 appears to be found exclusively in Barbados aloes, is now termed Bar- 

 balo'in, in order to distinguish it from allied substances occurring in 

 Natal and Socotrine aloes. 



Barbaloin was discovered by T. and H. Smith of Edinburgh in 1851,' 

 and was described (1851) by Stenhouse. From good qualities of the 

 drug it can be obtained, according to Tilden,'' as a crystalline mas.s, to 

 the extent of 20 to 25 per cent., but in others it appears to occur partly 

 amorphous or in a chemically altered state. Barbaloin is a neutral sub- 

 stance, crj'stallizing in tufts of small yellow prisms. These crystals 

 represent hydrated aloin, and part with one molecule of water (= 2G9 

 per cent.) by desiccation in vacuo, or by the prolonged heat of a water- 

 bath. Barbaloin, C"H^O^^ + H"0, dissolves sparingly in water or alcohol 

 but very freely if either liquid be even slightly warmed ; it is insoluble 

 in ether. 



The solutions alter quickly if made a little alkaline, but if neutral 

 or slightly acid, are by no means very prone to decomposition. By 

 oxidation with nitric acid, barbaloin yields, as Tilden (1872) has shown, 

 about a third of its weight of chr^^sammic acid, besides aloetic, oxalic, 

 and picric acids. It easil}^ combines with bromine to form yellow 

 needles ofBromcdoin, O^ffoBr'O"; Chlomloin, C^-'H"«C1''0" + 6H^0, cry- 

 stallizing in prisms, has likewise been obtained. 



In examining Natal aloes in 1871, we observed it to contain a 

 distinct crystalline body, much less soluble than the ordinary aloin of 

 Barbados aloes. We have accordingly named it Xotalmn. 



Nataloin exists naturally in Natal aloes, from which it can be easily 

 prepared in the crude state, if the drug is triturated with an equal 

 weight of alcohol at a temperature not exceeding 48° C. This will 

 dissolve the amorphous portion, from which the cr3^stals should be 

 separated by a filter, and washed with a small quantity of cold spirit. 

 From 16 to 25 per cent, of crude nattiloin in pale yellow crystals may be 

 thus extracted. When purified by crystallization from methylic alcohol 

 or spirit of wine, it forms thin, brittle, rectangular scales, often with one 

 or more of their angles truncated. The formula assigned to nataloin by 

 Tilden, which is supported by the composition of the acetyl derivative 

 he has succeeded in obtaining, is C^H^O". 



At 155° C, 60 parts of alcohol, 35 of methylic alcohol,^ 50 of acetic 

 ether, 1236 of ether, and 230 of absolute alcohol, dissolve respectively 

 one part of nataloin. It is scarcely more soluble in warm than in cold 

 spirit of wine, so that to obtain crystals it is best to allow the solution 

 to evaporate spontaneously. Water hot or cold dissolves it very 

 sparingly. Nataloin gives off" no water when exposed over oil of vitriol, 

 or to a temperature of 100° C. By the action of nitric acid, it afibrds 

 both oxalic and picric acids, but no chrysammic acid. It appears not 



^ Most beautiful specimens have been pre- ^ The best crystals can be got by this 



sented to each of us by these gentlemen. solvent. 



^Pharm. Journ. April 28, 1872. 845.— 

 See also Nov. 5, 1870. 375. 



