8 COMMERCIAL FEEDING STUFFS. 



METHODS OF ANALYSIS. 



In the analysis of these foods, the following determinations were 

 made: Moisture, ash, ether extract, crude protein, crude fiber, starch, 

 sucrose, reducing sugars, and pentosans. The methods used for 

 moisture, ash, ether extract, crude -protein, and crude fiber are the 

 official methods of the Association of Official Agricultural Chemists/ 

 The methods for pentosans and starch are those provisionally adopted 

 by this association, and the methods for determining sucrose and 

 reducing sugars those used by the miscellaneous laboratory for 

 determining these constituents in most cattle foods and forage crops. 

 These methods are as follows : 



DETERMINATION OF PENTOSANS. 



(1) PURIFICATION OF PHLOROGLUCOL. 



Heat in a beaker about 300 cc of hydrochloric acid (specific gravity 1.06) and 11 

 grams of phloroglucol added in small quantities at a time, stirring constantly until it has 

 almost entirely dissolved. Some impurities may resist solution, but it is unnecessary 

 to dissolve them. Pour the hot solution into a sufficient quantity of the same hydro- 

 chloric acid (cold) to make the volume 1,500 cc. Allow it to stand at least over night 

 better several days to allow the diresorcol to crystallize out, and filter immediately 

 before using. The solution may turn yellow, but this does not interfere with its use- 

 fulness. In using it, add the volume containing the required amount to the distillate. 



(2) DETERMINATION. 



Place a quantity of the material, chosen so that the weight of phloroglucid obtained 

 shall not exceed 0.300 grams, in a flask, together with 100 cc of 12 per cent hydrochloric 

 acid (specific gravity, 1.06) and several pieces of recently heated pumice stone; place 

 the flask upon a wire gauze, connect it with a condenser and apply heat, rather 

 gently at first, and so regulate as to distil over 30 cc in about ten minutes, the 

 distillate passing through a small filter paper. Replace the 30 cc driven over 

 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 tha flask, 

 and continue the process until the distillate amounts to 360 cc. To J,he complete 

 distillate gradually add a quantity of phloroglucol (purified if necessary) dis- 

 solved in 12 per cent hydrochloric acid, and thoroughly stir the resulting mixture. 

 The amount of phloroglucol used should be about double that of the furfural expect ed. 

 The solution first turns yellow, then green, and very soon an amorphous greenish 

 precipitate appears, which grows rapidly darker, until it finally becomes almost black. 

 Make the solution up to 400 cc with 12 per cent hydrochloric acid and allow to stand 

 over night. 



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

 asbestos felt, wash carefully with 150 cc of water in such a way thai the water is n<t 

 entirely removed from the crucible until the very last. Then dry for four hours at the 

 temperature of boiling water, cool ami weigh in a weighing bottle, the increaM- in 

 weight being reckoned as phloroglucid. To calculate the furfural, pentoaes, or j>en- 

 toeans from the phloroglucid, use the following formulas: 



For weight of phloroglucid (a) under 0.03 gram: 



Furfural =(a+0.0052)X 0.5170 

 Pentoses =(a+0.0052)X 1.0170 

 Pento8ans=(a+0.0052) X0.8949 



U. S. Dept. Agr., Bureau of < h. inistry, Bui. 107, p. 57. 



