4 Cellulose 



acids * Swedish ' filter paper of good quality contains from 

 o-o3~o*o5 p.ct. ash constituents, and constitutes the purest 

 form of cellulose with which we can deal. 



Cellulose and Water. Cellulose Hydrates. All 

 vegetable structures in the air-dry condition retain a certain 

 proportion of water or hygroscopic moisture, as it is termed 

 which is readily driven off at 100, but reabsorbed on exposure 

 to the atmosphere under ordinary conditions. The mean per- 

 centage of this * water of condition ' varies from 6 to 1 2 in the 

 several celluloses ; and in any particular cellulose will vary 

 on either side of this mean number to the extent of 1-2 p.ct. 

 with the extreme range of ordinary atmospheric conditions 

 of temperature and tension of aqueous vapour. 



The authors have made experiments on the * drying ' of cellu- 

 loses in a current of carbonic acid gas. The * hygroscopic 

 moisture' (6 -8 p.ct.) is rapidly driven off from the air-dry fibrous 

 celluloses at 90-100, and there is a further small loss of water 

 (ip.ct.) on raising the temperature to 180. The loss at 100- 

 120 is 0*5 p.ct. ; after that the loss is slow and probably due to de- 

 composition. Gelatinous celluloses in the form of films (see p. 28) 

 when dried at 90- 1 00 also show a further loss, but much greater at 

 higher temperatures. Thus in one experiment an air-dry film lost 

 8-6 p.ct. on drying at 100 ; an additional 3-9 p.ct. on raising 

 the temperature to 160. 



In an earlier age of the science the question might have 

 been discussed whether this absorption and retention of water 

 is a chemical or physical phenomenon ; but this is rather a 

 question of terms. The main points to be noted are (i) the 

 property of attracting water is a property of the cellulose 

 substance itself, and is not in any way dependent upon the 

 form in which it occurs. The amorphous modifications of the 

 celluloses obtained by solution and reprecipitation in various 

 ways (infra) are equally * hygroscopic.' 



(2^ The phenomenon is definitely related to the presence of 



