24 Cellulose 



cellulose has been made the starting-point of two series of 

 synthetical derivatives of cellulose, which must be briefly 

 described. 



An interesting account of Mercer's researches on this subject 

 is given in 'The Life and Labours of John Mercer' (E. A. Par- 

 nell, London, 1886), a work which maybe particularly commended 

 to the young student. 



From the points established by Mercer in connection with this 

 reaction the following may be further noted : 



At ordinary temperatures a lye of 1-225-1-275 sp.gr. effects 

 ' mercerisation ' in a few minutes ; weaker liquors produce the 

 result on longer exposure, the duration of exposure necessary being 

 inversely as the concentration. Reduction of temperature produces, 

 within certain limits, the same effect as increased concentration. 

 The addition of zinc oxide (hydrate) to the alkaline lye also increases 

 its activity. Caustic soda solution of noo sp.gr., which has only a 

 feeble ' mercerising ' action, is rendered active by the addition of the 

 oxide in the molecular proportion, Zn(OH) 2 : 4NaOH. 



The condition of the cotton also affects the result. The ordi- 

 nary bleaching process, with its treatment with boiling alkaline 

 lye under pressure, brings the cellulose into a condition relatively 

 unfavourable, the best results being obtained by a preparatory 

 treatment consisting of (i) boiling with water only, (2) bleaching 

 in a warm bath (60-70 C.) of hypochlorite (bleaching powder) pre- 

 pared with addition of lime. 



In regard to the physical changes of the fibre-substance result- 

 ing from the treatment, the effects in the mass, i.e. in yarn or cloth, 

 are seen in shrinkage of linear dimensions, with a corresponding 

 increase in thickness. The percentage of shrinkage observed is 20- 

 25. The ' mercerised' fabric shows an increase of strength, i.e. re- 

 sistance to breaking strain, of from 40-50 p.ct. Another important 

 feature of the * mercerised ' fabrics is an increased dyeing capacity. 

 These changes of form and in properties were investigated by 

 W. Crum (Chem. Soc. Journ. 1863). 



The changes in the minute structure of the cell he showed 

 to be similar to those which accompany the process of ripening 

 i.e. from the flattened riband form of a collapsed tube to the 

 cylindrical form resulting from the uniform thickening of the 



