BY J. H. MAIDEN. 141 



under the teeth. It swells up in cold water to many times its 

 original bulk, the outer portion becoming so transparent that it is 

 difficult to distinguish it in the liquid, the inner portion remaining 

 translucent and whitish. When pressed between the fingers the 

 soaked gum does not feel gelatinous, although slightly adhesive. 



In water it does not dissolve entirely on continued boiling, the 

 liquid becoming slightly cloudy, with small filmy particles floating 

 about in it. On acidifying with hydrochloric acid, the cloudiness 

 and the particles alike disappear. The whole of the gum is pre- 

 cipitated when alcohol is added to this acidified solution. If this 

 precipitate be then filtered off, the greater part is soluble in water. 

 The undissolved portion is soluble in potash of *1 per cent., but 

 not in acidified solutions. If the potash solution be acidified with 

 either acetic or hydrochloric acid, a glairy mass results. 



It is instructive to compare this gum with Tragacanth and 

 Sterculia gum.* 



This gum agrees with Tragacanth in regard to the points given 

 in the table at p. 384 (oj>. cit.), with the following exceptions : — 

 It does not entirely dissolve on prolonged boiling; forms a granular 

 jelly like Sterculia gum on treatment with cold water, while 

 Tragacanth forms a smooth viscid mass under similar circum- 

 stances ; contains no starch. 



It agrees with Tragacanth on the following points : — A yellowish 

 colour with alkalis on heating; formation of the substance denoted 

 by Giraud as pectic acid.f (I have in another place J commented 

 on the unsatisfactory position of these so-called pectic bodies.) 



Conclusion. — Echinocarpus gum appears to occupy an inter- 

 mediate position between Sterculia gum and Tragacanth, with 

 greater resemblance to the latter. 



The specific gravity of the gum is 1*481. 



* See my paper, " Sterculia Gum ; its similarities and dissimilarities to 

 Tragacanth," Pharm. Journ. (3), xx. 381. 

 + Pharm. Journ. (3), v. 766. 

 X Chem. and Drugg. of Austral. , Feb., 1890. 



