CELLULOSE. 203 



firmness, and swells up in water, forming a lubricous 

 mass. 



By long-continued action of sulphuric acid on cellu- 

 lose, it is completely dissolved by subsequent addition 

 of water, and this solution contains dextrin (wood dex- 

 trin), which is converted into grape-sugar by boiling 

 the solution, water being assimilated. 



Cellulose-nitrate (Pyroxilin, gun-cotton). "When 

 cotton, which has been cleansed by means of dilute 

 caustic soda, washing and drying, is inserted for five 

 minutes into a mixture of 1 volume concentrated 

 sulphuric acid and 2 volumes fuming nitric acid, then 

 thoroughly washed with water and dried, it is changed 

 into gun-cotton, although its external appearance re- 

 mains the same. It burns up instantaneously in con- 

 tact with a burning body, and acts exactly like gun- 

 powder, but more violently. It is insoluble in alcohol, 

 acetic, hydrochloric, and nitric acids. Ordinary gun- 

 cotton consists of a mixture of several compounds. 

 Hence, according to the method of preparation, it 

 possesses somewhat different properties. When pre- 

 pared by adding 1 part of cotton to a warm concen- 

 trated solution of 20 parts of dry, finely-pulverized 

 saltpetre in 31 parts of concentrated sulphuric acid, 

 allowing to stand for twenty-four hours, and after- 

 wards thoroughly washing and drying, it has the pro- 

 perty of dissolving in a mixture of ether with a little 

 alcohol. This solution (collodion), on the evaporation 

 of the ether, leaves the compound behind in the form 

 of a transparent, flexible coating, impervious to water. 

 If, on the other hand, very concentrated nitric and 

 sulphuric acids are employed in the preparation, there 

 is obtained an exceedingly explosive compound of the 

 composition C 6 H 7 (O.N0 2 ) 3 2 (trinitrocellulose), entirely 

 insoluble in ether and alcohol. Wood, flax, tow, and 

 paper conduct themselves in a similar manner towards 

 the acid mixture. 



Triacetyl-cellulose, C 6 H 7 (O.C 2 H 3 0) 3 2 . Is ob- 

 tained by heating cotton or Swedish filter paper with 



