94 METHODS OF ANALYSIS. 



18. Preservatives. 



Add 5 cc of dilute sulphuric acid to 100 cc of beer from wliich the alcohol 

 Las been driven off, and determine as directed under " XXVII. Food Preserva- 

 tives," page 179. 



(a) SULPHITES AND SULPHUROUS ACID. 



Determine in 50 cc of the beer as directed under " XXVII. Food Preserva- 

 tives," page 187. 



(b) FLUORIDS METHOD OF BLABEZ. 



Thoroughly mix the sample and heat 150 cc to boiling. Add to the boiling 

 liquid 5 cc of a 10 per cent solution of barium acetate. Collect the precipitate 

 in a compact mass, using to advantage a centrifuge, wash upon a small filter 

 and dry in the oven. Transfer to a platinum crucible, first breaking up the dry 

 precipitate and then adding the filter ash to the crucible, and complete the 

 determination, as directed under " XXVII. Food Preservatives," page 186. 





