38 WILD AND CULTIVATED COTTONS 



humidity and temperature in the factory, and his work should be 

 consulted. (Gf. Cross and Bevan, ' Paper-making,' 1900, pp. 95-6.) 



2. Mineral Constituents. This is the percentage of ash left after 

 burning the fibre. 



3. Hydrolysis. This may be characterised as the bleaching of 

 fibres. It can be accomplished by either acids or alkalis, the latter 

 from choice. A solution of 1 per cent, caustic soda is used. The 

 fibre is boiled in this for five minutes, a second portion for one hour. 

 The loss in weight in the former is the proportion that yields to the 

 solvent action of the alkali ; in the latter, the degree of degregation, 

 due to the hydrolytic action. 



4. Cellulose. A specimen of fibre, having been boiled in the 1 per 

 cent, solution of caustic soda, is washed thoroughly, then exposed for 

 an hour, at the ordinary temperature, to an atmosphere of chlorine 

 gas. It is then removed, washed, and treated with a solution of 

 sodium sulphite, which is slowly raised to the boil. After two or 

 three minutes' boiling, it is washed, dried, and weighed. 



The percentage yield of cellulose, on the raw fibre thus obtained, 

 is the most important criterion of its composition and value. 



5. Mercerising. The action of concentrated solutions of the 

 alkalis upon vegetable fibres is an important feature in the diagnosis 

 of their composition. The structural modifications which the cotton 

 fibre undergoes by this treatment, were originally observed and made 

 known by Mr. John Mercer in 1850 hence the expression ' mer- 

 cerising.' So far as the chemistry of the action has been made out, 

 the hydration changes which it sets up are in the direction of 

 resolving the fibre substance into cellulose and non-cellulose. The 

 fibre is thoroughly wetted with a concentrated solution (33 per cent.) 

 of the alkali, which is allowed to act for one hour. The fibre is then 

 washed, dried, and weighed. The cells shorten in length, but swell 

 out in diameter, become transparent and gain both in strength and 

 weight, and moreover turn glossy and silky in appearance. 



Mercer observed that when cotton fabrics were soaked in a 

 solution of caustic soda of sp. gr. 1'3 or 1-4 they became stronger and 

 fuller, converting thin and coarse cloth into strong and fine, and at 

 the same time giving greatly increased and improved powers of 

 receiving colour and of making the colours more permanent. Thus 

 three very important and remarkable changes were, he pointed out, 

 effected at one and the same operation : the fibre became stronger , 

 finer, and manifested an increased affinity for tinctorial reactions. 



