4 DETEBMINATION OF SUGARS IN GRAIN AND CATTLE FOODS. 



cipitate, and allow to stand 15 minutes. At this point the solution 

 may safely stand overnight if desired. Make up to the mark with 

 distilled water and pass through a folded filter, carefully saving all 

 of the filtrate, to which add enough anhydrous sodium carbonate to 

 precipitate all the lead, allow to stand 15 minutes, and pour onto 

 an ashless filter. Over 75 cc of filtrate should be obtained. Test 

 the filtrate for lead with a small quantity of dry sodium carbonate, 

 and if any precipitation occurs add more anhydrous sodium carbonate 

 and refilter. Use 25 cc of this clear filtrate together with 25 cc of 

 water for the determination of reducing sugars by the method of 

 Munson and Walker. 1 In a 100-cc graduated flask, place 50 cc of the 

 same filtrate, add a small piece of litmus paper, and neutralize with 

 acetic acid; then add 5 cc of concentrated hydrochloric acid, and let 

 stand overnight for inversion. (Standing 48 hours does not ap- 

 parently affect the results.) Then pour the inverted solution into a 

 400-cc beaker and neutralize with anhydrous sodium carbonate; 

 return it to the 100-cc flask and make up to the mark. Filter, if 

 necessary, and use 50 cc for the determination of total sugars as invert 

 by the method of Munson and Walker. 2 



The amount of cuprous oxid or copper obtained (see page 7) in 

 either the reducing or the total sugar determination represents the 

 sugar contained in 2 grams of the material. Therefore the weights 

 of the invert sugar when divided by 2 and multiplied by 100 give the 

 respective per cents of sugar as invert. Substract the per cent of 

 reducing sugars before inversion from the per cent of total sugar 

 after inversion, both calculated as invert, and the difference multi- 

 plied by 0.95 gives the per cent of sucrose (see page 13 for expression 

 of results). Since the insoluble material of the grain or cattle food 

 occupies some space in the flask as originally made up, it is necessary 

 to correct for this volume. Results of a large number of determina- 

 tions on various materials have shown the average volume of 12 

 grams of material to be 9 cc; therefore the correction factor for 12 

 grams in 300 cc is 0.97, and the percentage figures for reducing sugar 

 and sucrose are to be multiplied by this factor to obtain the true 

 amounts. 



STATEMENT OF SODIUM CARBONATE DIGESTION METHOD. 



Lately the cold-water extraction method has .been improved. 

 Realizing that the trouble experienced with this method of extrac- 

 tion was largely due to the activity of enzyms, it was suggested that a 

 small percentage of sodium carbonate be added to the water used 

 for extraction to inhibit their action. 3 Based upon this suggestion, 



i U. S. Dept. Agr., Bureau of Chemistry Bui. 107, Revised, p. 241. 



* Ibid. 



J. Ind. Eng. Chem., 1909, 1: 299. 



