X] FOOD PRESERVATIVES 147 



the mark with lime water. Mix and filter through a dry filter. To 50 cc. of the 

 filtrate add N/1 sulphuric acid until the pink color disappears, then add methyl 

 orange, and continue the addition of the acid until the yellow color is changed to 

 pink. Boil for about 1 minute to expel carbon dioxid. Cool, and carefully add 

 N/5 sodium hydroxid until the liquid assumes a yellow tinge, avoiding an excess 

 of the alkali. All the boric acid is now in a free state with no uncombined sulphuric 

 acid present. Add a little phenolphthalein, and an equal volume of neutral glycerol. 

 Titrate with N/5 sodium hydroxid until a permanent pink color is produced. About 

 10 grams of mannitol may be substituted for the glycerol in this determination. 

 At the end of the titration add an additional 2 grams and continue the titration if 

 the pink color is discharged. Repeat the alternate addition of mannitol and alkali 

 until a permanent end point is reached. 



One cc. of N/5 sodium hydroxid is equivalent to 0.0124 gram of boric acid. 



FORMALDEHYDE. 



16 PREPARATION OF SAMPLE. 



If solid or semi-solid, macerate 200-300 grams of the material with about 100 cc. 

 of water in a mortar. Transfer to a short-necked, 500-800 cc. copper or glass dis- 

 tillation flask and make distinctly acid with phosphoric acid, connect with a con- 

 denser and distil 40-50 cc. In the case of highly colored liquids, the same method 

 of preparation should be employed. 



In the case of meats and fats, extract the formaldehyde with alcohol and use the 

 filtrate. In the case of fat, heat the mixture above the melting point of the fat to 

 insure thorough extraction. In the case of milk, shake with an equal volume of 

 strong alcohol and use the filtrate. Shake other liquids with an equal volume of 

 strong alcohol and filter from any insoluble matter. 



QUALITATIVE TESTS. 



17 Phenylhydrazin Hydrochlorid Method.^ 



Mix 5 cc. of the distillate, as prepared under 16, or of an alcoholic solution or 

 extract obtained as directed above, with 0.03 gram of phenylhydrazin hydrochlorid, 

 and 4 or 5 drops of a 1% ferric chlorid solution. Add slowly and with agitation, 

 in a bath of cold water to prevent heating the liquid, 1-2 cc. of concentrated sul- 

 phuric acid. Dissolve the precipitate by the addition either of concentrated sul- 

 phuric acid (keeping the mixture cool) or alcohol. In the presence of formaldehyde 

 a red color develops. 



This method gives reliable reactions for formaldehyde in solutions of formalde- 

 hyde varying from 1 part in 50,000 to 1 part in 150,000. Acetaldehyde and benz- 

 aldehyde give no reaction when treated by this method and do not interfere with 

 the reaction given by formaldehyde. 



18 II ehner Method.^ 



Mix about 5 cc. of the distillate, obtained in 16, with an equal volume of pure 

 milk, or a 1-2% solution of egg albumen, in a test tube and underlay with strong 

 commercial sulphuric acid without mixing. A violet or blue color at the junction 

 of the two liquids indicates formaldehyde. This color is given only in the presence 

 of a trace of ferric chlorid or other oxidizing agent. As pointed out by Hehner, 

 milk may be treated directJy by this method and gives positive tests in the presence 

 of 1 or more parts of formaldehyde per 10,000. Some other articles of food rich 

 in proteins, for example, egg albumen, give the reaction in the presence of water 

 without the addition of milk. 



