ADULTERATIONS OF MILK 227 



hydroxid. A distinct bluish-green or green reaction is obtained 

 if formaldehyd is present in quantities of 1 : 70,000 or more. 



2. Treat 15 c.c. of the milk or the distillate thereof with 1 c.c. 

 of a dilute solution of phenylhydrazin hydrochlorid, then a few- 

 drops of dilute ferric chlorid solution, and, finally, with concen- 

 trated hydrochloric acid. A red color changing to orange yellow 

 indicates presence of formaldehyd (Rimini's method). 



3. Prepare the reagent by dissolving 1 gram phloroglucol and 

 20 grams sodium hydroxid in sufficient water to make 100 c.c. 

 To 10 c.c. of milk add, by means of a pipet, 2 c.c. of this reagent, 

 placing the end of the pipet on the bottom of the tube in such a 

 manner that the reagent will form a separate layer. A bright 

 red color is formed at the zone of contact if formaldehyd is present. 



Formaldehyd can be detected by heating a few cubic centi- 

 meters of the milk with an equal volume of hydrochloric acid and 

 adding 1 or 2 drops of a 1 per cent, ferric chlorid solution. A 

 violet color appears when formaldehyd is present. , 



Determination of Formaldehyd in Milk {Leach). — "To 100 c.c. 

 of milk add 1 c.c. of 1 : 3 sulphuric acid and subject to distillation 

 in a 500-c.c. Kjeldahl nitrogen flask, using a low circular evaporat- 

 ing burner to avoid frothing. Collect 20 c.c. of the distillate and 

 determine the formaldehyd as follows: Treat 10 c.c. of tenth- 

 normal silver nitrate with 6 drops of 50 per cent, nitric acid in a 

 50-c.c. flask, add 10 c.c. of a solution of potassium cyanid contain- 

 ing 3.1 grams KCN in 500 c.c. of water, and make up to the 50 

 c.c. mark. Shake, filter, and titrate 25 c.c. of the filtrate with 

 tenth-normal ammonium sulphocyanate, using ferric chlorid as an 

 indicator. 



"Acidify another portion of 10 c.c. of tenth-normal silver nitrate 

 with nitric acid, add 10 c.c. of the potassium cyanid solution to 

 which the above 20 c.c. of the formaldehyd distillate has been 

 added. Make up the whole to 50 c.c, filter and titrate as before 

 25 c.c. of the filtrate with tenth-normal ammonium sulphocyanate 

 for excess of silver. 



"The amount of potassium cyanid used up by the formaldehyd, 

 in terms of tenth-normal ammonium sulphocyanate, is found by 

 multiplying by 2 the difference between the two results, and the 

 total formaldehyd is calculated by multiplying by 3 the amount 

 found in the 20 c.c. of the distillate." 



Detection of Borax and Boric Acid. — Method of the Associa- 

 tion of Official Agricultural Chemists: "Render decidedly alkaline 

 with lime-water about 25 grams of the milk and evaporate to 

 dryness on a water-bath. Ignite the residue to destroy organic 

 matter. Digest with about 15 c.c. of water, add hydrochloric 

 acid, drop by drop, until all is dissolved, and add 1 c.c. in excess. 



