250. CRUDE FIBRE. 257 



is dissolved by ammonio-sulphate of copper,^ 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 Q,f chloride of zinc render cellulose capable of assuming a 

 blue colour with iodine ;^ but in some instances the reaction is 

 found to fail,^ 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. * 



§ 250. Crvde 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 ethei: in succession, dried and 

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

 little undecomposed wood-gum, Hgnin, and suberin, as well a« 

 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.* 



^ I prepare this reagent by precipitating hydrate of copper from a soluticm 

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

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



' 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 

 wiih it. 



' On cellulose of fungi, see Masing, Pharm. Zeitschr. f. Kussland, is. 38i5, 

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

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

 alkalies eonverts it into ordinaiy cellulose. But is it not probable that such 

 treatment actually produces a chemical change ? 



* On cellulose see Payen, Annal. d. Sciences natureUes, xi. 21, xiv. 88 ; 

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

 ibid, xlviii. 8 ; Sohlossberger and Dopping, ibid. lii. 106; Schlossberger, ibid, 

 cvii. 24, 1858 ; F^ii^t, Comptes rendus, Ixiii. 209, 1861 ; Knop and Schneder- 

 mann, Joum. f. prakt. Chem. xzxix. 363, xl. 389 ; Hennebeig, AnnaL d. 

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

 1879. 



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

 Landwirthsch. Jahrb. Supp. vi. 101, 



17 



