48 PHARMACY 



ing of a pill or gelatin capsule to a tough leathery insoluble sub- 

 stance. Alcohol may prevent the precipitation of alkaloidal salts by 

 tannic acid, as in tinctures. 



Rule 9. Chloral hydrate decomposes to chloroform under the 

 influence of strong alkalies ; and when mixed with camphor, menthol, 

 thymol, and similar substances, undergoes a physical change to a 

 liquid. 



EuLE 10. Alkaloidal salts are incompatible with — (a) Alka- 

 lies — the precipitate is the pure alkaloid, (b) Tannic acid — the 

 precipitate is the insoluble tannate. (c) Iodine, iodides, and bro- 

 mides — precipitate is the iodide or bromide, (d) Mercuric bichlor- 

 ide — the precipitate is the insoluble double salt. 



Quinine in addition is especially precipitated by salicylates and 

 benzoates. 



All these precipitates are more soluble in alcohol than water, so 

 may not show in tinctures and other alcoholic liquids. 



Rule 11. Glucosides are incompatible for the most part with 

 lead acetate and tannic acid, and are decomposed by the mineral 

 acids. 



