250. CRUDE FIBRE. 257 



is dissolved by ammonio-sulphate of copper, 1 and reprecipitated 

 in an amorphous condition by dilute acids ; but that of many 

 fungi is either insoluble or taken up to a slight extent only, and 

 then with great difficulty. Concentrated sulphuric acid and syrupy 

 solution of chloride of zinc render cellulose capable of assuming a 

 blue colour with iodine f but in some instances the reaction is 

 found to fail, 3 and Schulze's reagent for cellulose, which is not 

 without its value as a micro-chemical reagent, cannot therefore in 

 such cases be employed for colouring the cell-wall. The facility, 

 too, with which cellulose can be converted into glucose varies. 

 Masing observes that fungus-cellulose undergoes the change more 

 easily than flax-fibre. 4 



250. Crude Fibre. From what has been said of the isolation 

 of cellulose, it follows that the crude fibre of the physiologist and 

 agricultural chemist cannot be exactly identical with that sub- 

 stance. To estimate the crude fibre, the material is generally 

 boiled for half an hour, first with 1 per cent, sulphuric acid, and 

 then with 1 per cent, caustic potash. The residue is exhausted 

 with cold water, alcohol, and ether in succession, dried and 

 weighed. In this crude fibre we may anticipate the presence of a 

 little undecomposed wood-gum, lignin, and suberin, as well as 

 part of the hydrocelluloses mentioned in 117, 244. 



An apparatus that may be used with advantage in this deter- 

 mination has been described by Holdefleiss. 5 



1 I prepare this reagent by precipitating hydrate of copper from a solution 

 of the sulphate by dilute caustic soda, rapidly filtering off, pressing and 

 dissolving in the requisite quantity of 20 per cent, solution of ammonia. 



2 The reagent known as Schulze's can be prepared by dissolving 25 parts 

 of dry chloride of zinc and 8 of iodide 'of potassium in 8| of water, and adding 

 as much iodine as the solution will take up when warmed for a short time 

 with it. 



3 On cellulose of fungi, see Masing, Pharm. Zeitschr. f. Russland, ix. 385, 

 1870. Eichter (Chem. Centralblatt, 483, 1881) has recently denied the 

 existence of a special fungus-cellulose as the prolonged action of caustic 

 alkalies converts it into ordinary cellulose. But is it not probable that such 

 treatment actually produces a chemical change ? 



4 On cellulose see Pay en, Annal. d. Sciences naturelles, xi. 21, xiv. 88 ; 

 Fromberg, Annal. d. Chem. und Pharm. lii. 113 ; Heldt and Kochleder, 

 ibid, xlviii. 8; Schlossberger and Popping, ibid. lii. 106; Schlossberger, ibid, 

 cvii. 24, 1858 ; Peligot, Comptes rendus, Ixiii. 209, 1861 ; Knop and Schneder- 

 mann, Journ. f. prakt. Chem. xxxix. 363, xl. 389 ; Henneberg, Annal. d. 

 Chem. und Pharm. cxlvi. 130, 1869 ; Koni^, Zeitschr. f. anal. Chem. xiii. 242, 

 1879. 



5 Compare Holdefleiss, Zeitschr. f. Anal. Chem. xvi. 498, 1877, and 

 Landwirthsch. Jahrb. Supp. vi. 101. 



17 



