1903.] PUBLIC DOCUMENT — No. 33. 73 



(c/) Perfected Methods'^ for the Deter7nination of the Pento- 

 mns. — Present Phloroglucol Method. 



Reagents. 



Twelve per cent, hydrochloric acid (specific gravity 1.06) : 

 275 c.c. cone, acid (specific gravity 1.20) to 725 c.c. water; 

 test with a hydrometer as 15° C. 



Phloroglucol solution (purified) : 11 grams are dissolved 

 in 300 c.c. hot 12 per cent, acid by constant stirring, made 

 up to 1,500 c.c. with cold acid, allowed to stand several 

 days for the diresorcinol to crystallize out, and filtered 

 immediately before use. 



Pumice stone : the stone is prepared by dropping it at 

 white heat into distilled water, and leaving it there until 

 required. 



Aniline acetate (test solution) : equal parts of aniline and 



50 per cent, acetic acid. 



Apparatus. 



Erlenmeyer flask, 300 c.c. ; Liebig condenser and Aubrey 

 connecting tube ; separatory funnel (open) ; graduated cyl- 

 inders ; beaker, 25 ounce ; Gooch crucible. 



Method. 

 A weight^ of material^ that will not ^deld over .300 gram 

 'of phloroglucid is brought into a 10-ounce Erlenmeyer flask, 

 together with 100 c.c. of 12 per cent, hydrochloric acid and 

 several pieces of pumice stone. The flask, placed on a wire 

 gauze, is connected with a Liebig condenser, and heat ap- 

 plied, gently at first, and regulated so as to distil over 30 

 c.c. into a graduated cylinder in ten minutes. The 30 c.c. 



^ The phenylhydrazine method will be found described in the twelfth report 

 of the Massachusetts State Experiment Station, p. 177, and in Bulletin No. 51, 

 Division of Chemistry, U. S. Department of Agriculture. The phloroglucol 

 method, as used in this laboratory for a number of years, is described in Bulletin 

 No. 51, just referred to, and in the ninth report of the Hatch Experiment Sta- 

 tion, p. 97. 



^ With material containing pentosans: 30 per cent., take 1 gram of material ; 

 25 per cent. , take 1.25 grams of material ; 20 per cent., take 1.50 grams of mate- 

 rial ; 15 per cent., take 2 grams of material; 10 percent., take 3.25 grams of 

 material; 5 per cent., take 5 grams of material. 



^ Previous extraction with ether is not warranted, except with materials of a 

 high fat content. 



