6o MILK ANALYSIS 



the examination of butter. It is equally adapted for the gen- 

 eral examination of fats and oils, and may be used for the de- 

 termination of the index of refraction as well. As these in- 

 struments are made by only one firm and are furnished with 

 directions for use, further description will not be required. 



Milk test. — The following test was proposed by Waterhouse : 

 50 CO. of fresh whole milk are placed in a 100 c.c. beaker, heated 

 nearly to boihng and a lump of the sample (5 to 10 grams) 

 stirred in, preferably with a wooden rod, until the fat is melted. 

 The beaker is placed in cold water and the stirring continued 

 until the temperature falls to the solidifying point of the fat. 

 Butter fat will be granular and not easily collected into a lump, 

 but oleomargarin will collect readily. 



Rejractometric Examination. — This is most satisfactorily 

 made by the oleorefractometer or the butyrorefractometer. 

 Jean prepares the sample for examination in the former as 

 follows: 30 grams of butter are melted in a porcelain dish at 

 a temperature not exceeding 50°, stirred well with a pinch or 

 two of gypsum, and allowed to settle out at the same temper- 

 ature. The supernatant fat is decanted through a hot-water 

 funnel plugged with cotton and poured while warm into the 

 prism of the apparatus, stirred with the thermometer until the 

 fat has cooled to 45°, and the deviation observed. Ether must 

 not be used for the solvent, as minute traces of it seriously 

 influence the result. 



Heating test. — Oleomargarin and butter exhibit char- 

 acteristic differences on heating, which may be utilized for 

 rapidly sorting a collection of samples. When butter is heated 

 in a small tin dish directly over a gas flame, it melts quietly, 

 foams, and may run over the dish. Oleomargarin, under 

 the same conditions, sputters noisily as soon as heated and 

 foams but little. Even mixtures of butter and other fats show 

 this sputtering action to a considerable extent. The effect 

 depends upon the condition in which the admixed water exists. 



