Dilute nitric acid at 60-80° (Cross and Bevan) and a dilute mixture of nitric and sulphuric acids (Lifschutz) have been employed for isolating cellulose from the lignocelluloses. Hoffmeister modifies the method of Schulze by substituting hydrochloric acid for the nitric acid. Treatment with the halogens associated with alkaline processes of hydrolysis is the basis of the methods of Hugo Muller (bromine water) and Cross and Bevan (chlorine gas). Lastly, the authors notice the methods based upon the action of the alkaline hydrates at high temperatures (180°) in presence of water (Lange), or of glycerin (Gabriel). The process of heating to 210° with glycerin only (Hönig) yields a very impure and ill-defined product.
For comparative investigation of these processes certain celluloses and cellulosic materials were prepared as follows:
(a) 'Rag' cellulose.—A chemical filter paper, containing only cotton and linen celluloses, was further purified by boiling with dilute acid and dilute alkali. After thorough washing it was air-dried.
(b) Wood cellulose.—Pine wood sawdust was treated by digestion for fourteen days with dilute nitric acid with addition of chlorate (Schulze). The mass was washed and digested with alkaline lye (1.25 p.ct. KOH), and exhaustively washed, treated with dilute acetic acid; again washed, and finally air-dried.
This product was found to yield 2.3 p.ct. furfural on distillation with HCl (1.06 sp.gr.).
(c) Purified wood.—Pine wood sawdust was treated in succession with dilute alkalis and acids, in the cold, and with alcohol and ether until exhausted of products soluble in these liquids and reagents.
In addition to the above the authors have also employed jute fibre and raw cotton wool in their investigations.
They note that the yield of cellulose is in many cases sensibly lowered by treating the material after drying at the temperature of 100°. The material for treatment is therefore weighed in the air-dry condition, and a similar sample weighed off for drying at 100° for determination of moisture.
The main results of the experimental investigation are as follows:—
Weende process further attacks the purified celluloses as follows: Wood cellulose losing in weight 8-9 p.ct.; filter paper, 6-7.5 p.ct., and the latter treated a second time loses a further 4-5 p.ct. It is clear, therefore, that the process is of purely empirical value.