358 CHEMICAL DISCOVERY AND INVENTION 



gelatinous precipitate. The solvent which is known as Schweizer's 

 reagent is made by immersing copper turnings in solution of 

 ammonia and bubbling air through it. The reaction with cellulose 

 has been turned to account in the manufacture of Willesden 

 Paper, which consists of a coarse paper the surface of which is 

 gelatinised and rendered waterproof by moistening it with the 

 copper-ammonia solution. Within the last few years this 

 solution of cellulose has been employed in one of the processes 

 for the production of artificial silk, to be referred to a little later. 



The action of caustic alkalis on the fibre of cotton was observed 

 and applied about 1850 by John Mercer, a well-known calico- 

 printer, and the product has long been known as " mercerised " 

 cotton. The effect of the alkali is to untwist the naturally 

 twisted flattened tubes of which cotton fibres consist, and thicken 

 their walls. The fabric thus treated presents a somewhat silky 

 gloss and is increased in strength. 



Another very remarkable reaction of cellulose was discovered 

 more than twenty years ago by Messrs. Cross and Bevan, well- 

 known authorities on this department of applied chemistry. 



If cellulose in any of its forms is treated with a concentrated 

 solution of caustic soda, and the altered (mercerised) cellulose 

 thus obtained is exposed to the action of carbon bisulphide, a 

 yellowish mass is formed in an hour or two which swells up 

 enormously on mixing with water and finally dissolves com- 

 pletely. This soluble compound appears to consist of a peculiar 

 cellulose xanthate, to which the formula NaS-CS-0-C 12 H 19 9 

 has been attributed. From a solution of this compound cellulose 

 is again precipitated by acids, by heat, or simply by long stand- 

 ing, in the form of a gelatinous mass appropriately termed 

 " viscose." This also is applied to the production of artificial 

 silk, the annual output of which was stated in 1914 to be 14 

 million pounds, the capital employed being 5,000,000. Viscose 

 is also largely used in the manufacture of photographic films. 



Another liquid which is capable of dissolving cellulose without 

 breaking up the molecule is a concentrated solution of zinc 

 chloride. This solution was at one time used in the production 

 of carbon filaments for electric glow lamps. 



Strong sulphuric acid dissolves cellulose forming a mixture of 

 sulphates, but if the acid is diluted with about half its volume 

 of water the cellulose does not dissolve, but is superficially 

 hydrated and gelatinised. Paper dipped into acid of this strength 



