66 MILK PRODUCTS 



adulteration may be detected by the change 

 in the refractive power of the serum as described 

 on page 42. H. C. Lythgoe, who has investi- 

 gated this question, finds that samples adulter- 

 ated with butter will give a refraction below 36.0. 

 Results may be confirmed by taking the ash 

 of the sour serum. A large amount of the 

 sample is taken (as the yield of serum is small), 

 soured with a pure culture of lactic acid bacillus, 

 or with a little sour milk, shaken in a bottle 

 until the fat and curd have separated, the serum 

 drawn off and the ash of 25 c.c. taken. It 

 should not be below 0.73%. The homogizing 

 of cream without the addition of fat can be 

 detected by microscopic examination. 



Formic Acid.-rRevis and Bolton state that 

 glucose containing this may be found in cream 

 and give the following method for its detection. 



100 grams are diluted with an equal weight of 

 water, 20 c.c. of a 20% solution of phosphoric 

 acid added, and 100 c.c. distilled, the end of the 

 condenser dipping below the surface of milk of lime 

 containing at least i gram of calcium hydroxid 

 and 2 c.c. of 3% acetic acid, free from formic. 

 The distillate is evaporated to dryness, sealed 

 in a small tube of hard glass, drawn out at one 

 end that dips into a small U-tube containing 

 2 c.c. of water, arranged so that none of the water 

 can be drawn into the tube, and heated until 



