FOOD PRESERVATIVE. 



(b) APPROXIMATE QUANTITATIVE ESTIMATION. 



Extract as directed under the quantitative estimation of salicylic acid, page 

 179, but acidify with hydrochloric or phosphoric acid instead of sulphuric acid, 

 determine the weight of sulphur in the residue, and multiply by ."..712 for the 

 weight of saccharin, expressed in grams. The results obtained by this method 

 are only approximate. 



4. Boric Acid and Borates. 

 (a) QUALITATIVE DETECTION. <* 



Render decidedly alkaline with lime water about 25 grams of the sample 

 and evaporate to dryness on a water bath. Ignite the residue to destroy 

 ! organic matter. Digest with about 15 cc of water, add hydrochloric acid, drop 

 by drop, until all is dissolved, and add 1 cc in excess. Moisten a piece of deli- 

 cate turmeric paper with the solution ; if borax or boric acid is present, the 

 paper on drying will acquire a peculiar red color, which is changed by ammo- 

 nium hydroxid to a dark blue-green, but is restored by acid. 



A preliminary test may be ma.de by immersing a strip of turmeric paper in 

 about 100 cc of liquid foods, to which about 7 cc of concentrated hydrochloric 

 acid has been added. Solid and pasty goods may be heated with enough water 

 to make them thoroughly fluid, hydrochloric acid added in about the proportion 

 ies || of 1 to 13, and tested in the same manner. 



(b) QUANTITATIVE ESTIMATION. & 



Render 100 grams of the sample decidedly alkaline with sodium hydroxid and 

 evaporate to dryness in a platinum dish. Ignite the residue thoroughly, heat 

 with about 20 cc of water, and add hydrochloric acid, drop by drop, until all 

 is dissolved. Transfer to a 100-cc flask, the volume not being allowed to 

 exceed 50 to 60 cc. Add 0.5 gram of calcium chlorid and a few drops of 

 phenolphthalein, then a 10 per cent solution of caustic soda until a permanent 

 slightly pink color is produced, and finally add 25 cc of limewater. Make the 

 volume up to 100 cc. Mix and filter through a dry filter. To 50 cc of the filtrate 

 add normal sulphuric acid until the pink color disappears, then methyl orange, 

 and continue the addition of the acid until the yellow is just changed to pink. 

 Boil to expel carbon dioxid. Add fifth-normal caustic soda until the liquid 

 assumes the yellow tinge, excess of soda being avoided. Cool the solution, add 

 a little phenolphthalein, and an equal volume of glycerin. Titrate with stan- 

 dardized sodium hydroxid until a permanent pink color is produced. 



One cubic centimeter of fifth-normal soda solution is equal to 0.0124 gram of 

 crystallized boric acid. 



5. Formaldehyde, 

 (a) PREPARATION OF SAMPLE. 



If the material be solid or semisolid, macerate from 200 to 300 grams in a 

 I mortar with about 100 cc of water until a sufficient degree of fluidity is obtained. 

 (Transfer to a short-necked distilling flask of copper or glass of from 500 to 800 

 jcc capacity and make distinctly acid with phosphoric acid. Connect the flask 



ith a glass condenser and distil from 40 to 50 cc. 



U. S. Dept. Agr., Division of Chemistry, Bui. 51, p. 113. 



6 Thomson's method, Button's Volumetric Analysis, 9th ed., p. 93. 



