60 METHODS OF ANALYSIS [Chap. 



bottom of a Soxhlet extractor designed for making extractions at temperatures be- 

 low 100°C. 



An extractor of this kind is furnished with a water jacket surrounding that por- 

 tion of the apparatus containing the sample but does not enclose the side tube which 

 carries the hot vapors to the condenser. 



Transfer the moistened fat-free leather to the extractor, and cover this with 

 another layer of cotton to avoid siphoning off solid particles. Maintain the tempera- 

 ture of the jacket surrounding the Soxhlet at 50°C. (1) Pour 200 cc. of water (in- 

 cluding that used in moistening the leather) into the Soxhlet and allow it to siphon 

 into the flask below, then heat and extract for an hour. Remove the flame and trans- 

 fer the extract to a liter graduated flask. Then add water and continue the ex- 

 traction as directed below, removing and transferring the extract to the liter 

 flask before each fresh addition of water. 



(2) Add 175 cc. of water and extract for 2 hours. 



(3) Add 175 cc. of water and extract for 3 hours. 



(4) Add 175 cc. of water and extract for 4 hours. 



(5) Add 175 cc. of water and extract for 4 hours. 



Transfer the last portion of the extract to the graduated flask. This gives 14 

 hours' extraction and an extract which does not exceed 1 liter in volume. Dilute to 1 

 liter at room temperature and mix thoroughly. 



7 Method 11. 



(This method is the same in principle as the official method of the American Leather 

 Chemists Association. i) 



Digest overnight 30 grams of the fat-free leather, obtained under 5, in approxi- 

 mately 200 cc. of water. Transfer the leather and extract to a percolator. Continue 

 the extraction by percolating with water at 50°C. Collect 2 liters of percolate, 

 regulating the flow of water at such a rate that 2 liters will be collected in 3 hours. 

 Dilute to volume at room temperature and mix thoroughly. 



To the extract, prepared according to 6 or 7, add a few drops of toluol to prevent 

 fermentation of sugars, and reserve for the determination of glucose, total solids, 

 soluble solids, and nontannins. 



O PREPARATION OP SOLUTION. 



To 200 cc. of the leather extract, as prepared under 6 or 7, add 25 cc. of a saturated 

 solution of normal lead acetate, mix thoroughly, and filter at once through a dry, 

 plaited paper, returning the first portions of the filtrate to the filter until the fil- 

 trate becomes clear. Keep the containers and the funnel covered during these opera- 

 tions. Without waiting for the entire filtrate to run through add 10-12 grams 

 of solid potassium oxalate, shake frequently during 15-20 minutes and filter through 

 a dry, plaited paper returning the "first runnings to the filter until the filtrate runs 

 clear. Pipette 150 cc. of the last filtrate into a 600 cc. Erlenmeyer flask, add 5 cc. of 

 concentrated hydrochloric acid and boil under a reflux condenser for 2 hours. Cool, 

 neutralize with solid sodium carbonate, using a little phenolphthalein as indicator, 

 transfer to a 200 cc. volumetric flask and complete to volume with water. Filter 

 through a double filter, and return the first runnings until the filtrate becomes 

 perfectly clear. Determine the dextrose in the filtrate immediately. 



