304 DETECTION OF ADULTERANTS AND PRESERVATIVES 



tube, add an equal volume of a saturated aqueous solution of picric 

 acid. A yellow precipitate will be produced in presence of any con- 

 siderable amount of gelatin, while smaller amounts will be indicated 

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

 remain perfectly clear." 



Detection of Preservatives 

 CARBONATE OR BICARBONATE OF SODA* (HILGER'S METHOD) 



Dilute 50 c-c. of milk with 250 c.c. of water. Heat and precipi- 

 tate with a small quantity of alcohol. Filter, evaporate the filtrate 

 to one-half its original volume and test with litmus for an alkaline 

 carbonate. 



FORMALDEHYDE (HEHNER'S METHOD) 



Dilute the milk with an equal volume of water. Fill a test tube 

 one-half full. Add commercial sulphuric acid, specific gravity 1.82- 

 1.84. The acid should be allowed to flow down the side of the tube 

 so as to avoid excessive mixing of acid and milk. If formaldehyde 

 is present a violet ring forms at the junction of milk and acid. By 

 this test the presence of one part of formaldehyde in two hundred 

 thousand parts of milk can be detected. When more than .05 per 

 cent formaldehyde is present the violet color does not appear. 



The same color reaction is obtained when the acid is added to 

 the milk in the Babcock test. 



Farrington and Woll 2 recommend the following method : 

 Measure 5 c.c. of milk in a white porcelain dish, add 5 c.c. of water, 

 and 10 c-c. of hydrochloric acid containing a trace of ferric chloride 

 (Fe 2 Cl 6 ). Heat the mixture. If formaldehyde is present a violet 

 color appears. 



BORIC ACID AND BORATES 3 



"Render decidedly alkaline with lime water about 25 grams of 

 the sample 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. Moisten a piece of delicate turmeric paper 

 with the solution ; if borax or boric acid is present, the paper on 



1 Barthel, Milk and Dairy Products. 



2 Farrington & Woll, Testing Milk and Its Products. 



3 United States Department of Agriculture, Bureau of Chemistry. Bulletin 

 107, 1912. 



