Condensed Milk and Milk Powder 231 



flask and shake well. Break up the emulsion which 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 (evapo- 

 rated 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 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 char- 

 acteristic 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." 



SALICYLIC ACID 1 



Acidulate 20 c.c. of milk with sulphuric acid and shake with 

 ether. Evaporate the ether solution and treat the residue with al- 

 cohol and a .little iron-chloride solution ; a deep violet color indi- 

 cates the presence of salicylic acid. 



HYDROGEN PEROXIDE 3 

 (Wilkinson and Peters' Method) 



Add four drops of an alcoholic solution of 4 per cent, benzi- 

 dine (paradiamidodephenyl) and 2 drops of acetic acid to 10 c.c. of 

 milk. If hydrogen peroxide is present the milk assumes a blue 

 color. .005 grams of hydrogen peroxide in 100 c.c. of milk can be 

 detected by this method. 



CHAPTER XXXII 



BACTERIOLOGICAL ANALYSIS 



It is not the purpose of this volume to discuss in detail the 

 technique of bacteriological analyses of the milk products described 

 herein. The methods and technique of determining the bacterio- 

 logical flora, quantitatively and qualitatively, are identical to those 

 used in the bacteriological study of milk and other food products, 

 and which are fully described in manuals on bacteriology. 



i Farrington and Woll, Testing Milk and Its Products 

 2 Barthel, Milk and Dairy Products 



