332 METHODS OF ANALYSIS [Chap. 



8 ASH INSOLUBLE IN ACID.^TENTATIVE. 



Proceed as directed under XXIV, 5. 



9 SOLUBLE AND INSOLUBLE ASH.— TENTATIVE. 

 Proceed as directed under K, 17. 



10 ALKALINITY OF THE SOLUBLE ASH.— TENTATIVE. 

 Proceed as directed under IX, 18. 



1 1 SOLUBLE PHOSPHORIC ACID IN THE ASH.-TENTATIVE. 



Acidify the solution of soluble ash, obtained in 9, with dilute nitric acid and 

 determine phosphoric acid (PaOjjas directed under I, 6 or 9. 



12 INSOLUBLE PHOSPHORIC ACID IN THE ASH.-TENTATIVE. 

 Determine phosphoric acid (P2O6) in the insoluble ash as directed under I, 6 



or 9. 



13 CHLORIN.-OFFICIAL. 

 Proceed as directed under III, 18. 



CAFFEIN. 



14 Gorter Method^. — Tentative. 



Moisten 11 grams of finely powdered coffee with 3 cc. of water, allow to stand 

 30 minutes and extract with chloroform for 3 hours in a Soxhlet extractor. Evap- 

 orate the extract, treat the residue of fat and caffein with hot water, filter through 

 a cotton plug and moistened filter paper and wash with hot water. Make up the 

 filtrate and washings to 55 cc, pipette off 50 cc. and extract 4 times with chloro- 

 form. Evaporate the chloroform extract in a tared flask, dry the caffein at 100°C. 

 and weigh. Transfer the residue to a Kjeldahl flask with a small amount of hot 

 water and determine nitrogen as directed in I, 18, 21 or 23. To obtain the weight 

 of caffein multiply the result by 3.464. 



1 5 Modified Stahlschmidt Method^. — Tentative. 



Weigh 3.125 grams of the finely powdered sample into a 500 cc. flask, add 225 cc. 

 of water (this volume will shrink to about 200 cc. by boiling), attach a reflux con- 

 denser and boil for 2 hours. Add 2 grams of dry basic lead acetate [VIII, 13 (C)] 

 and boil 10 minutes more. Cool, transfer to a 250 cc. graduated flask, fill to the 

 mark, filter through a dry filter, measure 200 cc. of the filtrate into a 250 cc. 

 graduated flask and pass hydrogen sulphid through it to remove the e.xcess of lead. 

 Make the solution up to the mark and filter through a dry filter. Measure 200 cc. 

 of this filtrate into an evaporating dish and concentrate to about 40 cc. Wash the 

 concentrated solution with as little water as possible into a small separatory funnel 

 and shake out 4 times with chloroform, using 25, 20, 15 and 10 cc, respectively. If 

 any emulsion forms, break it up with a stirring rod and run the separated portions of 

 chloroform through a 5 cm. filter paper into a small, tared Erlenmeyer flask. Evap- 

 orate off the chloroform on the steam bath, or recover the chloroform by attaching 

 the flask to a condenser and distilling to a small volume. Dry the fine, white crystals 

 of caffein to constant weight at 75°C. Test the purity of this residue by deter- 

 mining nitrogen as directed in I, 18, 21 or 23 and multiplying by the factor 3.464. 



