CH. XIl] GLUCOSIDES. 255 



generally better to proceed at once to (7) than to try 

 precipitating with other metallic salts. 



(7) Shaking with hide powder or strips of raw 

 hide (gelatin method). 



The hide powder or strips of raw hide are thoroughly 

 soaked in cold water, which is frequently changed and 

 then added to the tannin solution in considerable quantity, 

 and allowed to remain in it for about 12 — 20 hrs. The 

 whole of the tannins are absorbed by the solid mass but a 

 considerable amount of organic matter nearly always goes 

 into solution during the process from the hide, and before 

 examining the filtrate for sugars it must be evaporated to 

 dryness on a water bath and taken up with 90 p.c. alcohol. 

 The alcohol is then completely distilled off and the residue 

 taken up with water. 



To determine whether a tannin is a glucoside 

 or not. 



If soluble in acetic ether the tannin can be separated 

 from free glucose by this means and the residue from 

 evaporation of the acetic ether used in the experiment. 

 If the tannin is not soluble in acetic ether it must 

 be precipitated by lead acetate, or some other con- 

 venient metallic salt, and the well-washed precipitate 

 used. 



The residue or precipitate is heated with 2 p.c. hydro- 

 chloric acid for about two hours on a water bath with a 

 reflux condenser — allowed to cool and filtered. The solu- 

 tion is treated with basic lead acetate as long as it causes 

 a precipitate, filtered and the excess of lead removed by 



