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 



"(o) 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. 



{h) Ash. — Determine the ash in 25 c.c. of the serum, ob- 

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

 100 c.c. indicate added water. 



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



