6 INTRODUCTORY 



acid (sp. gr. 1*42) and sulphuric acid (sp. gr. 1-84) for 

 one hour at the ordinary temperature. It is then 

 removed, allowed to drain for a few moments, and 

 transferred to a beaker containing a large volume 

 of water. After the fibre has been washed free from 

 the acid, it is heated with water until boiling com- 

 mences, and is finally dried in the water-oven. The 

 increase in weight is noted. In general, the increase 

 in weight on nitration bears a direct relation to the 

 other chemical constants. 



By the process of nitration the celluloses are con- 

 verted into their nitrates, giving a corresponding 

 increase in weight. The lignocelluloses furnish bright 

 orange-coloured products, whilst those of the pecto- 

 celluloses are colourless, or nearly so. 



Cellulose. The fibre is boiled for five minutes with 

 a solution of dilute sodium- hydroxide (i per cent. 

 Na 2 O), is washed free from alkali, and, while still 

 moist, is exposed to the action of chlorine gas for one 

 hour ; in some cases a longer exposure is necessary. It 

 is then washed and treated with a solution of sodium 

 sulphite, which is slowly heated until it boils ; after 

 two or three minutes' boiling, the product is collected 

 on a calico filter and washed ; it is afterwards treated 

 with acetic acid (20 per cent.) and again washed, dried, 

 and weighed. 



When the chlorinated fibre is immersed in the 

 sodium sulphite solution, a brilliant purple or crimson 

 coloration is produced if the fibre belongs to the 

 lignocellulose type, whilst in the case of non-lignified 

 fibres, the solution remains practically colourless. 



In this method of determining the percentage of 

 cellulose, the non-cellulose substance is rendered 

 soluble and removed, whilst the true cellulose is not 

 attacked. The percentage of true cellulose in a fibre 

 is the most important criterion of its composition and 

 value. A good fibre contains 75 to 80 per cent., or 

 even more. 



Acid purification. The fibre is put into acetic 

 acid (20 per cent.), which is slowly heated until it 

 boils ; the fibre is removed, washed first with alcohol 

 and afterwards with water, and then dried and weighed. 



