DAIRY PRODUCTS. 125 



(b) METHODS OF EXAMINATION OF BUTTER FAT. 

 See methods under " XIX. Edible Fats and Oils," page 129. 



7. Qualitative Tests of Butter, 

 (a) MICROSCOPIC EXAMINATION. OFFICIAL. 



Place a small portion of the fresh unraelted sample, taken from the inside of 

 the mass, on a slide, add a drop of pure sweet oil, cover with gentle pressure, 

 and examine with a one-half to one-eighth inch objective for crystals of lard, etc. 

 Examine the same specimen with polarized light and a selenite plate without 

 use of oil. Pure fresh butter will neither show crystals nor a particolored 

 3eld with selenite. Other fats melted and cooled and mixed with butter will 

 usually present crystals and variegated colors with the selenite plate. 



For further microscopic study dissolve from 3 to 4 cc of the fat in 15 cc of 

 jther in a test tube. Close the tube with a loose plug of cotton wool and allow 

 to stand from twelve to twenty-four hours at 20 to 25 C. When crystals form 

 it the bottom of the tube, they are removed with a pipette, glass rod, or tube, 

 placed on a slide, covered, and examined. The crystals formed by later deposits 

 nay be examined in a similar way. 



(b) SPECIAL TESTS FOB RENOVATED (PROCESS) BUTTER AND OLEO. 



(1) FOAM TEST. PROVISIONAL. 



Heat 2 or 3 grams of the sample, either in a spoon or dish, over a free flame, 

 True butter will foam abundantly, whereas process butter will bump and sput- 

 er, like hot grease, without foaming. Oleo behaves like process butter, but 

 chemical tests will determine whether the sample is oleomargarine or butter. 



(2) APPEARANCE OF THE MELTED FAT. PROVISIONAL. 



Melt from 50 to 100 grams of butter or process butter at 50 C. The curd 

 'rom butter will settle, leaving a clear supernatant fat. On the other hand, 

 he supernatant fat in the case of process butter does not assume that clear 

 ippearance, but remains more or less turbid. 



(3) MICROSCOPIC EXAMINATION. PROVISIONAL. 



Place a bit of the butter or process butter on a glass slide, cover it and press 

 t into a thin film with cover glass. Examine immediately with a polarizing 

 nicroscope magnifying from 100 to 140 diameters. When a selenite plate is 

 Dlaced between the slide and the lower nicol a normal butter will give a uni- 

 'ormly blue colored field, showing the absence of fat crystals. 



(c) DETECTION OF BORIC ACID. PROVISIONAL. 



Melt about 25 grams of the sample on the water bath, pour off the fat from 

 (the aqueous solution that settles, slightly acidify the aqueous solution with 

 Ibydrochloric acid, and test in the usual manner with turmeric paper for boric 

 iicid. (See p. 183, under " XXVII. Food Preservatives.") 



(d) DETECTION OF ANNATTO AND SAFFRON. 

 CORNWALL'S METHOD. PROVISIONAL. 



Dissolve 5 grams of the fat in 50 cc of ether in a wide tube and shake the 

 ;solution vigorously with 12 to 15 cc of a very dilute solution of potassium 

 bydroxid, which must still be alkaline after it separates from the ether solution. 



