300 DETECTION OF ADULTERANTS AND PRESERVATIVES 



Determination of Added Water by the Acetic Serum the Sour 

 Serum and the Copper Serum Methods ^ 



ACETIC SERUM. TENTATIVE 



"(a) Zeiss immersion refractometer reading. To 100 c.c. of 

 milk at a temperature of about 20 C. add 2 c.c. of 25 per cent acetic 

 acid (sp. gr. 1.035) in a beaker and heat the mixture, covered with 

 a watch glass, in a water bath for twenty minutes at a temperature 

 of 70 C. Place the beaker on ice water for ten minutes and sepa- 

 rate the curd from the serum by filtering through a 12.5 cm., folded 

 filter. Transfer about 35 c.c. of the serum to one of the beakers that 

 accompanies the control-temperature bath used in connection with 

 the Zeiss immersion refractometer, and take the refractometer read- 

 ing at exactly 20 C., using a thermometer graduated to tenths of a 

 degree. A reading below 39 indicates added water ; between 39 

 and 40, the addition of water is suspected. 



(b) Ash. Transfer 25 c.c- of the serum to a flat-bottomed 

 platinum dish and evaporate to dryness on a water bath. Then heat 

 over a low flame (to avoid spattering) until the contents are thor- 

 oughly charred, place the dish in an electric muffle, preferably with 

 pyrometer attached, and ignite to a white ash at a temperature not 

 greater than 500 C. (900 F.). Cool and weigh. Express the re- 

 sult as grams per 100 c.c. Results below 0.715 gram per 100 c.c. 

 indicate added water. Multiply by the factor 1.021 (dilution of the 

 acetic serum being 2 per cent) to obtain the result on the sour 

 serum ash. 



SOUR SERUM. TENTATIVE 



"(a) Zeiss immersion refractometer reading. Allow the milk 

 to sour spontaneously, filter and determine the immersion refrac- 

 tometer reading of the clear serum at 20 C- A reading below 38.3 

 indicates added water. 



(b) Ash. Determine the ash in 25 c.c. of the serum, ob- 

 tained in (a), as directed in (b). Results below 0.730 gram per 

 100 c.c. indicate added water. 



Journal of the Asso. of Official Agr. Chemists, Vol II., No. 8, Nov. 15, 1916. 



