60 Cellulose 



B. OXIDATIONS IN ALKALINE SOLUTION. (i) Hypo- 

 chlorites, in dilute solution ( < i p.ct.) and at ordinary tem- 

 peratures, have only a slight action upon cellulose ; a fact of 

 the highest technical importance, since hypochlorite of lime 

 (bleaching powder) is the cheapest of all soluble oxidising 

 compounds, and the most effective oxidant of the coloured 

 impurities which are present in the raw cellulose fibres or 

 formed as products of alkaline hydrolysis. 



While the normal celluloses withstand these bleaching oxida- 

 tions, there are many celluloses widely differentiated from the 

 cotton type which are eminently oxidisable, and, at the same 

 time, susceptible of hydrolysis. The 'celluloses' of esparto and 

 straw are of this kind (see p. 84), and the economic bleaching of 

 paper pulps prepared from these raw materials can hardly be 

 expected to follow upon the same lines as that of 'rag' pulp 

 (cotton and linen). A study of the factors involved in the pro- 

 cess will be found in a paper entitled ' Some Considerations in the 

 Chemistry of Hypochlorite Bleaching' (J. Soc. Chem. Ind. 1890). 

 These factors are in addition to temperature and concentration 

 (CL,O) of the bleaching solution the nature of the base in union 

 with the hypochlorous acid, and its proportion to the acid. A 

 knowledge of the operation of these factors will enable the bleacher 

 to control a process which is usually carried out on an entirely 

 empirical basis. 



The resistance of cellulose to the action of these solutions 

 necessarily has its limits, and when these are exceeded, the 

 fibre-substance is oxidised and disintegrated, and an oxy- 

 cellulose results. These effects are rapidly produced by the 

 joint action of hypochlorite solutions and carbonic acid. The 

 oxycellulose formed in this way acquiring the property of selec- 

 tive attraction for certain colouring matters notably the basic 

 coal tar dyes its presence in bleached cloth is easily detected 

 by a simple dyeing treatment consisting in immersing the 

 oxidised fabric in a dilute solution (0*5-2 'o p.ct.) of one of 

 these dye stuffs, e.g. methylene blue. Local over-oxidation 



