SCIENCE AND INDUSTRY. 
acetate and 10 Ibs. of sulphur chloride. The anhydride is finally distilled off. 
The cast iron appears to be quite suitable. The resulting product is a mixture 
of acetic anhydride and acetic acid, and the maximum yields (90 per. cent.) 
were obtained when the proportions by weight-of the acetate to the chloride 
were as 100 to 67. The crude anhydride contains 75 per cent. acetic anhydride, 
and is distilled in a copper vessel over copper oxide to fix the sulphur, which is 
stated to have an injurious effect on cellulose ‘acetate. Commercial acetic 
anhydride contains 80 to 90 per cent. anhydride, and 10 to 20 per cent. of acetic 
acid. ; 
3. Acetic Acid must be 98.5 per cent. pure, and be free from sulphur and 
organic sulphur compounds, chlorides, &c. ‘A process of manufacture of cellu- 
lose acetate has been worked out which yields a product complying with the 
British Air Board’s specifications of .1918. The catalyst used throughout is 
sulphuric acid of 90 per cent. strength, which is mixed with the acetylating 
acid (30 to 40 per cent. of acetic anhydride and the remainder of acetic acid) 
before being added to the cotton waste. Incorporation is performed in a phos- 
- phor bronze jacketed incorporator, and the process takes about 11 hours, during 
which cold brine is circulated through the jacket. The product is an amber- 
coloured opaque stiff dough. This is ripened in a copper vessel heated gradually _ 
in a water bath. At the'end of 13 to 15 hours the material resembles in its 
viscosity and appearance a light-coloured treacle. A sample taken and pre- 
cipitated forms tough and nearly transparent flakes. It is practically equiva- 
lent to cellulose triacetate. The final product desired is a partially ‘hydrated 
modification of this. An aqueous solution containing 50 per cent. of acetic acid 
is added to the syrup, the quantity varying according to the excess of acetic 
anhydride present, between 80 and 120 ems. per 100 ems. of cellulose. 
Hydration occupies 12 to 16 hours at a constant temperature. Precipitation 
 i8 effected by adding water to the syrup. ‘The precipitate is washed acid free 
and dried at a low temperature (40 to 60 deg. C.). The product is soluble in 
acetone. s ; 
- Acetic acid. in the waste solutions is recovered as sodium acetate, and is 
used over again.. The maximum quantity of sulphurie acid used is about 20 
per cent. of the weight of cotton waste. The cellulose acetates as produced at 
present have a tendency to instability. The causes of this are under investiga- 
tion. The quantity of acetic anhydride used is an important matter, and is 
controlled by many factors, e.g., temperature, per cent. of ‘moisture in cotton 
waste, and ratio of sulphuric acid to cotton waste. ; 
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