174 COFFEE 



legumin or vegetable casein. Polstorff obtained 0.25% of trigonel- 

 line. 



The extraction and estimation of the total caffeine-content of 

 coffee-beans is not a simple matter. The various proposed methods 

 of procedure may be divided into four groups : 



( 1 ) Extraction of caffeine by means of boiling water and subse- 

 quent treatment of the infusion with lime, magnesium, litharge, or 

 basic lead acetate to precipitate the tannin, etc. 



(2) Treatment of the material with lime and magnesium or 

 ammonia; and extraction with chloroform. 



(3) Extraction of the caffeine in the material directly by means 

 of aqueous sodium benzoate or salicylate with or without an alkali, 

 and subsequent treatment of the alkaline liquid with chloroform. 



(4) Gomberg's method whereby caffeine is extracted by means of 

 water and the alkaloid is precipitated in acid solution as a periodide. 



These methods are described in Allen's Comm. Org. Anal. ed. 4, 6 

 (1912) 607-614. The method I used with greatest success is a form 

 of that described in group i, and is known as 'Allen's Modification 

 of Stahlschmidt's Method.' Outline as follows: 



Take 12 grms. of coffee (finely powdered). 



Boil with 500 c.c. of water for 6 hrs. under a reflux condenser. 



Filter off extract (the residue being washed with hot water on 

 the filter). 



Dilute with water to 600 c.c. 



Heat to boiling. 



Add 4, grms. of powdered lead acetate; stir well to remove coloring 

 matter. 



Attach reflux condenser and boil for 10 minutes. 



(If, on removing heat, the precipitate does not curdle and settle 

 readily, leaving the liquid colorless, add more lead acetate and repeat 

 the boiling.) 



Pass through dry filter. 



Collect 500 c.c. of filtrate and evaporate to 50 c.c. 



Add a little sodium phosphate to precipitate the remaining lead. 



Filter; wash precipitate; evaporate total filtrate to 40 c.c. 



Extract caffeine by shaking with at least four portions of chloro- 

 form. 



