DECOMPOSITION OF NON-NITROGENOUS ORGANIC MATTER 453 



are of importance in the formation of wood and skeletal structure of 

 various plants. The formula for pentosans is (C 5 H 8 04) n , yielding, 

 on hydrolysis, C 5 H 10 O 5 or pentoses. The quantitative method of de- 

 termining pentosan is based on the formation of a pentose from the 

 pentosan, and of furfural from the pentose on further heating with 

 acid. Pentosans are determined quantitatively by (1) the phloro- 

 glucinol method, 77 (2) the bromine titration method, 78 or (3) by the 

 colorimetric estimation of furfural. 79 



A weighed quantity of material (also soil or culture medium) is distilled with 

 12 per cent HC1 until the distillate gives no further coloration with aniline acetate. 

 All connections in the distilling apparatus should be of glass. The distillate is 

 made up to 500 cc. with 12 per cent HC1. Standard, approximately 0.1 N sodium 

 bromide-bromate solution (25 cc.) is pipetted into each of four well-stoppered 

 bottles, 200 cc. of the distillate is added to each of two bottles and 200 cc. of 12 

 per cent HC1 to the two other bottles. These are allowed to stand in the dark 

 for one hour, and. after the addition of 10 cc. of 10 per cent KI solution, the 

 liberated iodine is determined by titration with 0.1 iV sodium thiosulfate solu- 

 tion. The number of cubic centimeters required by the sample is subtracted 

 from the number required by the blank, the difference being a measure of the 

 furfural present. One cubic centimeter of 0.1 N sodium thiosulfate = 2.4 

 mgm. furfural. 



Humus soils are rich in pentosans or substances which yield fur- 

 fural on boiling with HC1. 80 Forest soil, with 23.42 per cent humus, 

 was found to contain 0.75 per cent pentosan; garden soil, with 9.85 per 

 cent humus, contained 0.39 per cent pentosan; sandy soil, with 2.68 

 humus, contained only 0.04 per cent pentosan. Shorey and Lathrop 81 

 found pentosans universally distributed in the soil, the pentosan car- 

 bon ranging from 1.3 to 28.53 per cent of the total carbon. As much 

 as 2.75 per cent pentosan was found in a North Dakota soil in which 

 flax had been grown for a number of years. The presence of pentosans 



77 Krober, E. Untersuchungen liber die Pentosanbestimmungen mittelst 

 der Salzsaure-Phloroglucinmethode nebst einigen Anwendungen. Jour. Landw., 

 48: 357-384. 1900. 



78 Powell, W. J., and Whittaker, H. The determination of pentosans in wood 

 cellulose. Jour. Soc. Chem. Ind. Trans., 43: 35-36. 1924. 



79 Youngburg, G. E., and Pucher, G. W. Studies on pentosan metabolism. 

 I. A colorimetric method for the estimation of furfural. Jour. Biol. Chem., 61: 

 741-746. 1924. 



80 Chalmot, G. de. Pentosans in plants. Amer. Chem. Jour., 16: 218-228. 

 1894; Note on pentosans in soils. Ibid., 229. 



81 Shorey, E. C., and Lathrop, E. C. Pentosans in soils. Jour. Amer. Chem. 

 Soc, 32: 1680-1683. 1910. 



