METHODS OF INVESTIGATION 5 



constituent (i to 2 per cent.) with changes in the 

 hygroscopic state of the atmosphere, all the other 

 results of analysis are expressed as percentages of the 

 dry fibre. 



4 s h t The percentage of ash is determined by com- 

 pletely incinerating the fibre and weighing the 

 residue. An abnormally large percentage of ash 

 usually indicates the presence of mineral impurity 

 introduced during the preparation of the fibre. 



a-PIydrolysis. The fibre is boiled for five minutes 

 with dilute solution of sodium hydroxide (i per cent. 

 Na 2 O), and is then washed free from alkali, dried, and 

 weighed. The loss in weight indicates the amount of 

 substance removed by the solvent action of the 

 alkali. 



^Hydrolysis. Another portion of the fibre is 

 boiled for an hour with alkali of the same strength. 

 In this case, the loss in weight includes not only the 

 substance removed by the solvent action, but also- 

 that rendered soluble by the " degrading " action of 

 the alkali. It is evident, therefore, that the difference 

 between the values obtained on a- and ^-hydrolysis 

 indicates the susceptibility of the actual fibre substance 

 to attack by hot, dilute caustic alkali. 



The results yielded by these determinations afford 

 an indication of the ability of the fibre to resist pro- 

 longed exposure to moisture and the attack of alka- 

 line liquids with which the fibre may be treated 

 during the processes of manufacture. 



Mercerisation. The fibre is left at the ordinary 

 temperature in contact with concentrated sodium 

 hydroxide solution (33 per cent. Na 2 O) for an hour. 

 It is afterwards thoroughly washed with cold water, 

 dried, and the loss of weight determined. The visible 

 effects of this treatment are generally a shrinkage in 

 length of the strands of fibre and the production of a 

 wavy and crinkled outline. The chemical effect 

 consists chiefly of hydration changes. The result of 

 the determination indicates the power of the fibre to 

 withstand the action of strong caustic alkali. 



Nitration. The fibre is submitted to the action of 

 a mixture of equal volumes of concentrated nitric 



