VIII] FOODS AND FEEDING STUFFS 111 



phuric acid. A violet color indicates the presence of diresorcin. A phloroglucin 

 which gives more than a faint coloration may be purified by the following method: 

 Heat in a beaker about 300 cc. of hyd ochloric acid (sp. gr. 1.06) and 11 grams of 

 commercial phloroglucin, added in small quantities at a time, stirring constantly 

 until it has almost entirely dissolved. Pour the hot solution into a sufficient quan- 

 tity of the same hydrochloric acid (cold) to make the volume 1500 cc. Allow it 

 to stand at least overnight, preferably several days, to permit the diresorcin to 

 crystallize out. Filter immediately before using. A yellow tint does not inter- 

 fere with its usefulness. In using it, add the volume containing the required amount 

 to the distillate. 



64 DETERMINATION. 



Place a quantity of the material, 2-5 grams, chosen so that the weight of phloro- 

 glucid obtained shall not exceed 0.300 gram, in a 300 cc. distillation flask, together 

 with 100 cc. of 12% hydrochloric acid (sp. gr. 1.06), and several pieces of recently 

 heated pumice stone. Place the flask on a wire gauze, connect with a condenser, 

 and heat, rather gently at first, and regulate so as to distil over 30 cc. in about 10 

 minutes, the distillate passing through a small filter paper. Rep'ace the 30 cc. 

 distilled by a like quantity of the dilute acid, added by means of a separatory funnel 

 in such a manner as to wash down the particles adhering to the sides of the flask, and 

 continue the process until the distillate amounts to 360 cc. To the total distillate 

 add gradually a quantity of phloroglucin dissolved in 12% hydrochloric acid and 

 stir thoroughly the resulting mixture. The amount of phloroglucin used should be 

 about double that of the furfural expected. The solution turns first yellow, then 

 green, and very soon an amorphous greenish precipitate appears, which grows 

 darker rapidly, till it becomes finally almost black. Make the solution up to 400 

 cc. with 12% hydrochloric acid, and allow to stand overnight. 



Filter the amorphous black precipitate into a tared Gooch crucible through an 

 asbestos mat, wash carefully with 150 cc. of water in such a way that the water is 

 not entirely removed from the crucible until the very last, then dry for 4 hours at 

 the temperature of boiling water, cool and weigh in a weighing bottle, the increase 

 in weight being reckoned as furfural phloroglucid. To calculate the furfural, pen- 

 tose, or pentosan from the phloroglucid, use the following formulas given by Krober: 



(1) For a weight of phloroglucid, designated by "a" in the following formulas, 

 under 0.03 gram, 



Furfural = (a + 0.0052) X 0.5170. 



Pentoses = (a + 0.0052) X 1.0170. 



Pentosans = (a + 0.0052) X 0.8949. 



In the above and also in the following formulas, the factor 0.0052 represents the 

 weight of phloroglucid which remains dissolved in the 400 cc. of acid solution. 



(2) For a weight of phloroglucid "a" over 0.300 gram. 



Furfural = (a + 0.0052) X 0.5180. 



Pentoses = (a + 0.0052) X 1.0026. 



Pentosans = (a + 0.0052) X 0.8824. 



For a weight of phloroglucid "a" between 0.03 and 0.300 gram use Krober's 

 table, 65, or the following formulas in which the factors were calculated from 

 Krober's tables by C. A. Browne, i' 



Furfural = (a + 0.0052) X 0.5185. 



Pentoses = (a + 0.0052) X 1.0075. 



Pentosans = (a + 0.0052) X 0.8866. 



