152 COMPOSITION OF THE BODY 



2. A few drops of ferric chlorid or ferric acetate. Blue or 

 green precipitate shows tannins. 



3. Ammoniacal solution of potassium ferricyanide. Presence 

 of tannins indicated by deep red color changing to brown. 



4. Lime-water, Ca(OH) 2 . Tannins shown by blue, brown or 

 red color or precipitate. 



Quantitative Determination of Tannins. Only one method 

 will be given here. If others are desired see Wiley, Principles and 

 Practice of Agricultural Analysis, Vol. III. 1897. 



Two and a half grams of gelatine are dissolved in water with 

 ten grams of alum, and the solution made up to one liter. This 

 solution and the solution of tannins are both heated to 7o°C. The 

 gelatine solution is then slowly added with constant stirring to the 

 solution of tannins. Continue to add the gelatine until the pre- 

 cipitate coagulates, and until the further addition of the reagent 

 causes no additional precipitation. Collect the precipitate, dry at 

 1 io°C and weigh. Fifty-four per cent, of the weight of the pre- 

 cipitate is pure tannin. 



Tests for Phloroglucin. — If the material extracted was 

 woody tissue phloroglucin may be present in the extract. As 

 this substance is soluble in ether, it may be removed by shaking 

 ether with the extract. The ether should be separated from the 

 aqueous solution by means of a separatory funnel and evaporated, 

 and the residue dissolved in water. To parts of this solution add : 



1. Hydrochloric acid and vanillin. Phloroglucin is indicated 

 by a reddish-violet color. 



2. Ferric chloride. A deep violet color will result if phloro- 

 glucin is present. 



223. Determination of Sugars and Dextrins. Finely ground 

 tissue should be extracted with ether, or benzine, to remove fats, 

 etc., and after being freed from the ether by drying in the air, the 

 residue should be extracted with water near the boiling point for 

 about an hour. The mass should then be thrown on the filter 

 and the filtrate treated with basic lead acetate to remove as much 

 as possible of the proteids. After filtering out any precipitated 



