KNOWLEDGE & SCIENTIFIC NEWS. 



[April, 1905. 



Coniiided I'll F. Shili.ington- Scales, f.k.m s. 



Fibrous Constituents 

 of Paper. 



{Continued from Page 68.) 



Chlor-zin'C iodine gives a characteristic bluish violet 

 reaction with celhilose, becoming reddish-brown to 

 claret-coloured for rag and similar fibres, and light to 

 dark yellow for lignified fibres. We have thus a ready 

 means of distinguishing the fibres by their colour re- 

 actions alone, which we may summarise as follows : — 

 Linen, cotton, hemp, reddish-brown to claret; esparto, 

 straw, and chemical wood-pulp, bluish-violet; mechani- 

 cal wood-pulp and jute, yellow. Jute may be more blue 

 than yellow, whilst manilla hemp — an entirely different 

 fibre to hemp itself — will be blue rather than red. 



With polarized light the fibres also behave 

 differently. The nicols being crossed so that the field 

 is dark, it will be seen that linen and hemp give a 

 brilliant play of colours, especially if the microscope 

 has a stage which can be rotated; jute gives these 

 colours in a rather less degree, cotton or wool still less; 

 whilst esparto, straw, and wood-pulp are colourless. 

 It will be observed also that the various structural 

 details of the fibres are brought out very clearly by 

 this method, and this is of service in making the final 

 examination, as it will be observed that neither the 

 chlor-zinc iodide differentiation nor that with polarized 

 light are necessarily quite determinative. 



The examination of the structural differences of the 

 various fibres is, however, the most difficult of all, and 

 requires more experience than is apparent at first sight, 

 not a little of the difficulty being due to the rough treat- 

 ment the fibres have undergone as already mentioned. 

 A study of the accompanying illustrations will assist the 

 reader in following the description. 



Cotton shows flat, ribbon-like fibres with a large 

 lumen about two-thirds of its total diameter, so that 

 the cylinder, being weak, has collapsed in places and 

 thus given rise to a sort of spiral twist which forms the 

 most characteristic distinction of this fibre. It should 

 be noted, however, that the boiling in caustic .soda 

 largely counteracts this twist, as does the breaking up 

 in process of manufacture, so that the absence of the 

 twisted appearance does not necessarily decide the 

 question. The fibres also show fine, lattice-like mark- 

 ings, and it will be observed that they are free from 

 thickening or knots. The ends are often laminated. 

 Taken altogether, the wide lumen, the spiral twist, the 

 markings, and the freedom from knots form charac- 

 teristic features which make cotton one of the easiest 

 fibres to distinguish. 



Linen and hemp are so much alike that it is almost 



impossible to distinguish them, but they are not often 

 found in the same classes of paper, or where identifica- 

 tion and separation from each other is necessary. The 

 fibres are smaller than those of cotton — about half as 

 thick — and they have a very small lumen, so small that 

 it often appears little more than a narrow central line. 

 In places, however, the pressure which the fibre has 

 undergone during pulping may have flattened out the 

 central canal so that it bears a strong resemblance to a 

 jute fibre or even to cotton. The frequent thickening 

 into knots is very characteristic, but otherwise the fibre 

 is fairly uniform in thickness, and cylindrical. There 

 are also numerous dark cross lines which come out well 

 under polarized light. The ends are often drawn out 

 into fine fibrillae. 



esporfo 



Jute fibres have a peculiarly uneven appearance. 

 The wall is thick and thin in places, and the central 

 canal varies prf>porfionately in width from a thin line 

 to a canal as broad as that of cotton, and all these 

 changes may be observed without moving the slide. 

 They also show cross-striations and knots, but less 

 frequently than linen or hemp. Jute is a very intract- 

 able fibre, and accordingly the fibres will be often ob- 

 served sticking together in parallel bundles. It is most 

 difficult to bleach, and its use is, therefore, almost en- 

 tirely confined to coarse papers. 



Straw fibres are smooth and even, cylindrical, uni- 

 form in diameter, and with a central canal of varying 

 size, but at intervals knots appear. Striations are 



