xxii] dairy products 295 



Fat. 



45 preparation of sample.— official. 



Melt the butter and keep in a dry place at about 60°C. for 2-3 hours or until the 

 water and curd have entirely separated. Filter the clear, supernatant fat through 

 a dry filter paper in a hot water funnel or in an oven at about 60°C. If the filtered 

 liquid fat is not perfectly clear, refilter. 



46 EXAMINATION. 

 Proceed as directed under XXIII. 



47 Microscopic Method. — Official. 



Place on a slide a small portion of the fresh, unmelted sample taken from the 

 inside of the mass, add a drop of pure olive oil, apply a cover-glass with gentle 

 pressure, and examine with a magnification of 120-150 diameters for crystals of 

 lard, etc. Examine the same specimen with polarized light and a selenite plate 

 without the use of oil. Pure fresh butter will show neither crystals nor a parti- 

 colored field with selenite. Renovated butter or 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 in a test tube 3-^ cc. of the fat in 15 cc. 

 of ether. Close the tube with a loose plug of cotton wool and allow to stand 12-24 

 hours at 20°-25°C. When crystals form at the bottom of the tube, remove with a 

 pipette, glass rod or tube, place on a slide, cover and examine under a microscope. 

 The crystals formed by later deposits may be examined in a similar way. Com- 

 pare with crystals obtained in the same way from samples of known purity. 



48 PRESERVATIVES.— TENTATIVE. 

 Proceed as directed under X. 



49 COLORING MATTERS.— TENTATIATE. 



Pour about 2 grams of the filtered fat, dissolved in ether, into each of 2 test tubes. 

 Into one of the tubes pour 1-2 cc. of hydrochloric acid and into the other about the 

 same volume of dilute potassium hydroxid solution. Shake the tubes well and 

 allow to stand. In the presence of azo dyes the test tube to which the acid has been 

 added will show a pink to wine-red coloration, while the potash solution in the 

 other tube will show no color. If, on the other hand, annatto or other vegetable 

 color has been used, the potash solution will be colored yellow, while no color will 

 be apparent in the acid solution. 



General test. — Proceed as directed under XI, particularly 3 and 24, for the detec- 

 tion of oil-soluble coloring matters and annatto. 



RENOVATED BUTTER AND OLEOMARGARINE. 



50 Foam Test.— Tentative. 



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

 butter will foam abundalitly, whereas process butter will bump and sputter, like 

 hot grease, without foaming. Oleomargarine behaves like process butter, but 

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



