COTTON FIBRE 39 



The exact degree of improvement effected with a standard mer- 

 cerising preparation might, it seems probable, be resorted to as a 

 method of testing the comparative merits of the fibres of different 

 species of cotton and of the staples produced experimentally at 

 cotton improvement farms. 



6. Nitration, Cotton, when treated with concentrated nitric acid, 

 is converted into explosive compounds, which are now recognised to 

 be nitrates of cellulose. All celluloses are similarly acted upon, and 

 the study of the resulting compounds is a necessary feature of the 

 diagnosis of fibres. For this purpose Cross and Bevan recommend, 

 as a nitrating fluid, a mixture of equal volumes of concentrated nitric 

 acid (sp. gr. T42) and sulphuric acid (sp. gr. T74). The fibre is sub- 

 jected to this for one hour at the ordinary temperature. 



This causes an increase in weight, the extent of which in one as 

 compared with another fibre is a point of great importance. The net 

 increase in fibres ranges from 5 to 55 per cent. 



7. Combustion: Carbon Percentage. A rapid process of ascer- 

 taining the carbon percentage was introduced by these chemists, 

 and consists in burning the substance with chromic anhydride in the 

 presence of sulphuric acid and leading over the gaseous products 

 into an apparatus in which their volume can be exactly measured. 

 Accepting cotton as typical cellulose, the amount of carbon obtained 

 by ignition is 44*4 per cent. The lower carbon percentages are from 

 40 to 43, the higher 45 to 50. In the former the pecto-celluloses are 

 included, and in the latter the ligno-celluloses. 



8. Acid, Purification. To clean a fibre and remove all accidental 

 impurities it is heated to boiling point in a 20 per cent, solution of 

 acetic acid, then dried and weighed. The loss of weight sustained 

 shows the impurities. 



Doubtless some of these methods and contrivances may not be 

 necessary when attention is confined to cotton. I have thought it 

 likely to prove useful, however, to record Mr. Cross's system of 

 examining the merits of all fibres in as nearly complete a form as 

 space would admit of in this work. 



Cuprammonia (Cuoxam). But it may be added that the value of 

 cuprammonia in the examination of cotton has been urged by many 

 writers. This was pointed out originally by Schweitzer, and detailed 

 shortly after by Charles O'Neill ('Calico Printing, Bleaching and 

 Dyeing '), and has since been elaborated in every direction by numerous 

 investigators and practical operators. (Cf. Greenish, I.e. p. 308.) 



