group, present the following characteristics : colourless sub- 

 stances insoluble in all simple solvents, generally but variably 

 resistant to processes of oxidation and hydrolysis, non-nitro- 

 genous, and having the empirical constitution characteristic 

 of the carbohydrates, i.e. C n H 2m O m . Their reactions are those 

 of 'saturated' compounds. Their empirical formulae and 

 relationships to the carbohydrates of low molecular weight 

 further indicate ' single-bond ' linking of their C atoms as 

 exclusively prevailing. It must be noted here that the typical 

 celluloses are not separated from the plant in a ' pure ' state, 

 but in admixture or in intimate chemical union- with other 

 compounds or groups of compounds. The latter are distin- 

 guished by greater reactivity, e.g. they readily yield to alkaline 

 hydrolysis (* pectic ' bodies), to oxidation (colouring matters), 

 or to the action of the halogens. In the latter is included 

 the very important group of lignified celluloses or lignocellu- 

 loses (woods) distinguished by the presence of keto-hexene 

 groups in union with the cellulose, and therefore combining 

 directly with the halogens. These points are sufficient to 

 indicate the principles underlying the general method adopted 

 in the laboratory for the isolation of cellulose from vegetable 

 raw material which consists in (i) Alkaline hydrolysis 

 boiling the tissue or fibre in solution of alkaline hydrates (1-2 

 p.ct. NaOH), and after washing (2) exposure to the action of 

 a halogen chlorine gas or bromine water at the ordinary 

 temperature, and (3) second alkaline hydrolysis boiling in 

 alkaline solutions, e.g. sodium sulphite, carbonate, or hydrate, 

 to complete the resolution and to dissolve away the products 

 formed from the non-cellulose constituents by the preceding 

 treatment. 



In the case of very refractory substances such as the hard 

 woods, it is sometimes necessary to repeat the treatment with 

 the halogen. After such treatment and thorough washing the 



