of acid. Heat nearly to the boiling point over the free flame, holding the casserole 

 by the handle and giving it a rotary motion to break up the curd. A violet coloration 

 indicates formaldehyde. 



, Insert also the phloroglucin method as provisional: 



4f 



(c) PHLOROGLUCIN METHOD. 



To the contents of the dish add 3 cc of a phloroglucin solution made by dissolving 

 1 gram of phloroglucin and 20 grams of sodium hydroxid in sufficient water to make 

 100 cc. A bright red coloration (not purple) indicates the presence of methyl alco- 

 hol in the original sample. When too little hydrogen peroxid is added an orange- 

 yellow color will slowly appear. The hydrogen peroxid, if not fully destroyed, will 

 give rise to a purple color of gradual formation. The cherry or raspberry red pro- 

 duced as a result of methyl alcohol appears quickly after the addition of the reagent, 

 and fades quickly unless quite intense. The intensity of the red color is in propor- 

 tion to the quantity of methyl alcohol present. If the wood alcohol be as much as 

 1 part to 20 of ethyl alcohol, its presence will be revealed by this test. 



On page 36, after " 7. Detection of Borax and Boric Acid," insert 

 the following: 



8. DETECTION OF BENZOIC ACID. 



Add 5 cc of dilute hydrochloric acid to 50 cc of the milk in a flask and shake to 

 curdle. Then add 150 cc of ether, cork the flask, and shake well. Break up the 

 emulsion w r hich forms by aid of a centrifuge, or if the latter is not available extract 

 the curdled milk by gently shaking with successive portions of ether, avoiding the 

 formation of an emulsion. & Transfer the ether extract (evaporated to small volume 

 if large in bulk) to a separatory funnel and separate the benzoic acid from the fat by 

 shaking out with dilute ammonia, which takes out the former as ammonium ben- 

 zoate. Evaporate the ammonia solution in a dish over the water bath till all free 

 ammonia has disappeared, but before getting to dryness add a few drops of ferric 

 chlorid reagent. The characteristic flesh-colored precipitate indicates benzoic acid. 

 Care should be taken not to add the ferric chlorid till all the ammonia has been 

 driven off, otherwise a precipitate of ferric hydrate is formed. 



a Leach, Ann. Kept. Mass. State Board of Health, 1902; Food and Drug Reprint, p. 23. 

 & A volume of ether largely in excess over that of the curdled milk has been found to be less 

 apt to form an obstinate emulsion. 



9. DETECTION ON SALICYLIC ACID. 



Proceed exactly as directed for benzoic acid. On applying the ferric chlorid to 

 the solution after evaporation of the ammonia, the well-known violet color indicates 

 salicylic acid, when present, <" 



c These methods for salicylic and benzoic acids while especially applied to milk, from which 

 the ether extracts both fat and preservative, are useful also with modifications for many 

 other food products. The extraction of the ether solution Avith dilute ammonia, whereby 

 the preservative is removed, permits the subsequent recovery of the ether by distillation. 



On page 36, ' c 8. Detection of Foreign Colors " should be renumbered 



On page 39, change heading "8" to "Detection of Foreign Colors," 

 inserting " (a) Cornwall's method c " before the method there given. 

 After this method insert the following: 



