X] 



FOOD PRESERVATIVES 



153 



FIG. 6. APPARATUS FOR DETECTION OF FORMIC ACID. 



40 DETERMINATION. 



For thin liquids like fruit juices, use 50 cc. For heavy liquids and semi-solids 

 like sirups and jams, use 50 grams diluted with 50 cc. of water. Place the sam- 

 ple in the flask (A), add 1 gram of tartaric acid, and connect as shown in Fig. 6, 

 the flask (B) having been charged previously with a suspension of 2 grams of barium 

 carbonate in 100 cc. of water. If much acetic acid is present, suflficient barium 

 carbonate must be used so that at least 1 gram remains at the end of the operation. 

 Heat the contents of flasks (.1) and (B) to boiling and distil with steam from the 

 generator (5), the vapor passing first through the sample in flask {A), then through 

 the boiling suspension of barium carbonate in (B), after which it is condensed, and 

 measured in the graduated flask (C). Continue the distillation until 1 liter of dis- 

 tillate is collected, maintaining the volume of the liquids in the flasks {A) and (B) 

 as nearly constant as possible by heating with small Bunsen flames, and avoid- 

 ing charring of the sample in the flask {A). After 1 liter of distillate has been col- 

 lected, disconnect the apparatus and filter the contents of flask (B) while hot, wash- 

 ing the barium carbonate with a little hot water. The filtrate and washings should 

 now measure about 150 cc. If not they should be boiled down to that volume. Then 

 add 10 cc. of the sodium acetate, 2 cc. of 10% hydrochloric acid, and 25 cc. of the 

 mercuric chlorid reagent. Mix thoroughly and immerse the container in a boil- 

 ing water bath or steam bath for 2 hours. Then filter on a tared Gooch, wash the 

 precipitate thoroughly with cold water and finally with a little alcohol. Dry in a 

 boiling water oven for 30 minutes, cool, weigh, and calculate the weight of formic 

 acid present by multiplying the weight of the precipitate by 0.0975. If the weight 

 of mercurous chlorid obtained exceeds 1.5 grams, the determination must be re- 

 peated, using more mercuric chlorid reagent or a smaller amount of sample. A blank 



