X] FOOD PRESERVATIVES 143 



(b) Dissolve the residue in 40-50 cc. of ether. Transfer the ether solution to 

 a separatory funnel and extract with 3 successive 15 cc. portions of 1% ammonium 

 hydroxid. (If fat is known to be present in the original ether e.xtract, extract the 

 latter directly with 4 portions of the ammonium hydroxid instead of 3.) Combine 

 the alkaline aqueous extracts, acidify, again extract with ether and wash the com- 

 bined ether extracts as directed above. Distil slowly the greater portion of the 

 ether, allow the remainder to evaporate spontaneously and proceed as directed in 5. 



5 DETERMINATION. 



Dissolve the residue, obtained in 4, in a small amount of hot water and, after 

 cooling, dilute to a definite volume (usually 50-100 cc), dependent on the amount 

 of salicylic acid present. If the solution is not clear, filter through a dry filter. 

 Dilute aliquots of the solution and treat with a few drops of 0.5% ferric chlorid 

 solution or 2% ferric alum solution. 



The ferric alum solution should be boiled until a precipitate appears, allowed to 

 settle, and filtered. The acidity of the solution is slightly increased in this manner, 

 but it remains clear for a considerable time, and the turbidity caused by its dilution 

 with water is much less and does not appear as soon as when the unboiled solution 

 is used. This turbidity interferes with the exact matching of the color. 



Compare the colors developed with that obtained when a standard salicylic acid 

 solution (containing 1 mg. of salicylic acid in 50 cc.) is similarly treated, using 

 Nessler tubes or a colorimeter. In either case, and especially with ferric chlorid, 

 avoid an excess of the reagent, although an excess of 0.5 cc. of 2% ferric alum solu- 

 tion may be added to 50 cc. of the comparison solution of salicylic acid without 

 impairing the results. 



BENZOIC ACID. 

 PREPARATION OF SAMPLE. 



6 General Method. 



If solid or semi-solid, grind the sample, and mix thoroughly. Transfer about 

 150 grams to a 500 cc. graduated flask, add enough pulverized sodium chlorid to 

 saturate the water in the sample, render alkaline with sodium hj^droxid solution 

 or milk of lime, and dilute to the mark with a saturated salt solution. Allow to 

 stand for at least 2 hours, with frequent shaking, and filter. If the sample contains 

 large amounts of matter precipitable by salt solution, it is advisable to follow a 

 method similar to that given under 7 (d). When alcohol is present, follow the 

 method given under 7 (C). When large amounts of fats are present, make an 

 alkaline extraction of the filtrate before proceeding as directed under 1 1 . 



7 Special Methods. 



(a) Ketchup. — Saturate the water in 150 grams of ketchup by adding 15 grams of 

 pulverized sodium chlorid. Transfer the mixture to a 500 cc. graduated flask, rins- 

 ing with about 150 cc. of saturated sodium chlorid solution. Make slightly alkaline 

 to litmus paper with strong sodium hydroxid solution and fill to the mark with satu- 

 rated salt solution. Allow to stand for at least 1 hours, shaking frequently. 

 Squeeze through a heavy muslin bag and then filter through a large folded filter. 



(b) Jellies, jams, preserves and marjnalades. — Dissolve 150 grams of the sam- 

 ple in about 300 cc. of saturated salt solution. Add 15 grams of pulverized sodium 

 chlorid. Make alkaline to litmus paper with milk of lime. Transfer to a 500 cc. 

 graduated flask and dilute to the mark with saturated salt solution. Allow to 



