DAIRY PRODI 



8. Detection of Gelatin. Provisional. 



121 



Prepare an acid solution of mercuric nitrate by dissolving mercury In twice its 

 weight of nitric acid of 1.42 specific gravity, and diluting this solution to 25 

 times its bulk with water. To 10 cc of the milk or cream to lie examined, add an 

 equal volume of the acid mercuric nitrate solution, shake the mixture, add 20 cc 

 of water, shake again, allow to stand five minutes, and filter. If much gelatin 

 is present the filtrate will be opalescent and can not be obtained quite clear. To 

 a portion of the filtrate contained in a test tube, add an equal volume of a 

 rated aqueous solution of picric acid. A yellow precipitate will be produced in 

 presence of any considerable amount of gelatin, while smaller amounts will be 

 indicated by a cloudiness. In the absence of gelatin the filtrate obtained will 

 remain perfectly clear. 



9. Detection of Formaldehyde. Provisional. 

 I T se the method described on page 183, under " XXVII. Food Preservatives." 



10. Detection of Borax and Boric Acid. Provisional. 

 Use the method described on page 183, under " XXVII. Food Preservatives." 



11. Detection of Benzoic Acid. Provisional. 



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 which forms by aid of a centrifuge, or if the latter is not avail- 

 able 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 ammonium 

 hydroxid, which takes out the former as ammonium benzoate. Evaporate the 



I ammoniacal solution in a dish over the water bath till all free ammonia has 



| disappeared, but before dryness is reached 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 until all the ammonia has 



(been driven off, otherwise a precipitate of ferric hydrate is formed. (See also 

 XX VII. Food Preservatives," p. 181.) 



12. Detection of Salicylic Acid. Provisional. 



Proceed exactly as directed for benzoic acid in the preceding section. On 

 )lying the ferric chlorid to the solution after evaporation of the ammonia the 

 ill-known violet color indicates salicylic acid. 



13. Detection of Foreign Color, 

 (a) LEACH'S METHOD. PROVISIONAL. 



Warm about 150 cc of milk in a casserole over the flame and add about 5 cc 

 )f acetic acid, after which slowly continue the heating nearly to the boiling 

 >int while stirring. Gather the curd, when possible, into one mass by the 

 irring rod. and pour off the whey. If the curd breaks up into small flecks 

 irate from the whey by straining through a sieve or colander. Press the 



