230 



KNOWLEDGE. 



[OCTOBEK 1, 1894. 



CELLULOSE AND SOME OF ITS MORE RECENT 

 APPLICATIONS. 



By Chas. a. Silbekkad, B.A., B.Sc. 



THOUGH cellulose is an invariable constituent of 

 plants, of whose cell-walls it forms the supporting 

 frame-work, it is rarely found pure, as, except in 

 the cellular tissue of the youngest shoots, it 

 always contains more or less ash. Still, cotton- 

 wool and Swedish filter-paper consist of the approximately 

 - pure substance, especially the latter after treatment with 

 hydrofluoric acid, whereby all mineral matter is extracted. 



However, the preparation of pure cellulose from any 

 material containing it — e.ij., cotton-wool — is not a matter 

 of great difficulty, it being only necessary to digest it 

 alternately with bromine water and a dilute alkaline 

 solution until the bromine water is no longer decolorized. 

 The fibre is then boiled in dilute alkali and washed in 

 turn in dilute acid, alcohol and ether, and finally dried. 



Thus prepared, it contains a certain amount of hygro- 

 scopic moisture, amounting to from seven to nine per cent. 

 of its weight ; when this is removed, the simplest com- 

 position deducible from analysis is C^Hj^Oj, but it seems 

 clear from its properties that its molecular weight must 

 be many times that represented by the foregoing formula. 



Solvents of Cellulose. — Celhilose is insoluble in all 

 ordinary solvents, but is dissolved by certain reagents, of 

 which the two following are the most important : (n) 

 Schweitzer's reagent, which consists of an ammoniacal 

 solution of cupric hydrate. From solution in this liquid 

 the cellulose may be reprecipitated on addition of acids, 

 alcohol, salt, or various other substances, in a gelatinous 

 state, drying to a material closely resembling gum arable 

 in appearance. (/<) A solution of zinc chloride in twice its 

 weight of hydrochloric acid. This solvent behaves very 

 similarly to the first mentioned, except that the cellulose 

 is reprecipitated on dilution. Sucli solution and reprecipi- 

 tation afi'ord a ready means of purification. 



The solvent power of tlie first named of the above 

 liquids is the basis of the manufacture of the so-called 

 paper lioiinls. For this purpose sheets of unglazed paper 

 are left in contact with the ammonio-cupric solution for a 

 short time — just long enough for the filires to be super- 

 ficially attacked. The requisite number of these sheets 

 are then placed one on top of the other, jiassed between 

 rollers and dried ; by this process they become united 

 together into a board-like material, impervious to water, 

 which property is retained at 100^ Cent. 



Action of Xitric Aeiil. — If cellulose, e.;/., blotting-paper, 

 be simply immersed in ordinary strong nitric acid (specific 

 gravity 1-42) it undergoes a curious transformation. Its 

 composition is unchanged, but the strength of the paper 

 is increased tenfold, while at the same time its linear 

 dimensions are diminished ten per cent. 



The action of stronger nitric acid and of mixtures of 

 nitric and sulphuric acid in the production of gun-cotton 

 and the various pyroxylines, as well as the preparation of 

 collodion by dissolving the last named in a mixture of 

 alcohol and ether, are too well known to need any further 

 account here ; but the peculiar properties of a mixture of 

 camphor and pyroxyline may be worth noting, as it is of 

 these two substances that ctlhihiiil consists. 



Celluloid was first prepared by Hyatt, of Newark, U.S.A. 

 It may be obtained either by direct addition of pyroxyline 

 to melted camphor, or by strongly compressing the two 

 together, or lastly by dissolving the two in some common 

 solvent, as ether- alcohol. 



The method usually adopted on the manufacturing scale 

 is a combination of the second and third above mentioned. 



The pyroxyline is prepared by treating unsized paper with 

 moderately strong nitric and sulphuric acids, whereby a 

 product is obtained consisting of a mixture of the tetra- 

 and penta-nitrates of cellulose. 



The camphor is dissolved in the minimum quantity of 

 alcohol, and this solution sprinkled upon the dry sheets of 

 pyroxyline in such quantity that there is one part of 

 camphor to two of pyroxyline. On the sheet so treated 

 another is placed, and the same process repeated, and so 

 on till a sufficient thickness is obtained. 



There is thus produced a translucent mass which is 

 worked between rollers, first in the cold and then at a 

 higher temperature ; it is next subjected to hydraulic 

 pressure at a temperature of about 60' Cent., for twenty- 

 four hours, and finally cut into sheets of the desired 

 thickness and dried for several days at a moderate heat. 

 The substance so obtained appears quite homogeneous, and 

 may be cut and turned in the cold or moulded under 

 pressure at a higher temperature. 



It is very readily coloured by pigments or dyes, which 

 may be either mechanically mixed in a state of powder 

 or dissolved with the camphor in the alcohol. 



Artifieial tortohcshell is produced on the same principle 

 as damascene steel, i.e., by welding together alternate 

 plates of differently tinted celluloids. 



As might be anticipated from its composition, it is 

 extremely inflammable, but has been shown to be non- 

 explosive under all conditions. 



Action of Sulphuric Acid. — Vegetable Parchment or Parch- 

 ment Paper. — If cellulose, e.r/., blotting-paper, be rapidly 

 passed through moderately strong sulphuric acid (specific 

 gravity lo — 1-G), and then well washed in water, it 

 acquires properties very similar to those of parchment. 

 The resulting preparation is now extensively used under 

 the names of vegetable parchment or parchment paper. 



This change is due to the conversion of the cellulose on 

 the surfaces of the paper into a peculiar modification known 

 as amyloid, which may be precipitated pure in a gelatinous 

 form by diluting a solution of cellulose in concentrated 

 sulphuric acid. 



If cellulose be left in contact with acid of specific 

 gravity 1-5 for some time, it becomes friable, forming a 

 substance called ln/dro-celliilose, which is soluble in alkalies. 

 By means of this reaction the cotton may be separated 

 from the wool in a mixed fabric, as the latter is unacted 

 upon . 



Action of Alkalies. — iferceri^ation. — If cotton cellulose 

 be treated with a concentrated solution of soda or potash 

 and tlien washed, it is found to have undergone a remark- 

 able change in properties. From the name of its discoverer 

 (Mercer) this change is termed wi'rceri::ation. 



The way in whicli Mercer was led to his discoveries ia 

 interesting as showing how one result may lead to another 

 wholly i.nconnected with it. He was making a series of 

 experiments to determine whether any alteration occurred 

 in the composition of a solution on filtering it, and in the 

 course of these he passed a strong solution of caustic soda 

 through several Ia3er3 of cotton-cloth. He certainly 

 found a considerable change in the composition of the 

 solution on filtering, but was able to fully account for it 

 by what turned out to be the far more important change 

 produced in that of the cotton-cloth, for this proved to 

 be approximately expressed by the formula C„Hj,,0. 

 NaOH ; and though, on washing, all the soda was removed, 

 the properties of the fibre were found to have undergone 

 a marked change. Their length was contracted to the 

 extent of twenty per cent., while at the same time there 

 was an increase of thirty to thirty-five per cent, in strength. 

 A still more important alteration was the increased affinity 



