92 PUBLIC HEALTH CHEMISTRY 



and ranges from 86-3 to 88-5, on average about 87-3. All 

 other animal fats give an average of 95-3. 



Valenta Test. Depends on the intermiscibility of butter 

 fat and strong acetic acid at a low temperature, whereas 

 animal and vegetable fats (except coco-nut oil) do not 

 mix until a much higher temperature is reached. Glacial 

 acetic acid (99 per cent) is used. Take a test tube and add 

 3 c.c. of the fat and 3 c.c. of the acid. Immerse it in hot 

 water to heat the contents, which are stirred all the while 

 by a thermometer. If the sample is pure butter fat, it will 

 have cleared at 40 C., and it is then allowed to cool, still 

 stirring, and the temperature noted on the first appearance 

 of turbidity. For butter fat this should be from 32 to 36 C. 

 Margarine fat will not clear under 75 C. An abnormally 

 low Valenta figure suggests the presence of coco-nut oil. * 



Specific Gravity of Butter Fat. Is now seldom taken at 

 ordinary temperatures, it being more convenient to take 

 it with the fat in a molten state, at 100 F. The fat at 

 110 F. is poured into an ordinary specific-gravity bottle, 

 which is then placed in water at 100 F. The stopper is 

 pushed home, and the bottle dried, cooled, and weighed. 

 The weight of the same bulk of water at 100 F. is similarly 

 ascertained, and the specific gravity calculated. Pure butter 

 fat ranges from 910-7 to 913-5, but mostly between 911 and 

 913. Margarine fat ranges from 901-5 to 906, at 100 F. 

 The specific gravity is also taken at 100 C. by the Sprengel 

 tube or the Westphal balance, and ranges thus : Margarine, 

 856 to 860 ; butter, 865-3 to 866-8 ; coco-nut oil, 868 to 

 872 compared with water at 15-5 C. 



Refractive Index. Is determined on a special instrument. 

 At 35 C. it varies for butter from 44 to 49, generally 46. 

 Margarine gives about 54, and coco-nut oil about 43. 

 Its use is less valuable now than formerly. 



Boric Acid. Is detected in the ash, as in the case of 

 milk. In order to prevent loss when ashing, a few drops of 

 milk-of-lime solution should first be added. To estimate, 

 take 25 grm. of butter in a beaker, add 25 c.c. of a solution 

 of lactose (6 per cent) and sulphuric acid (4 c.c. of N/i 

 per cent). Melt in water-oven, mix by stirring, allow to 

 settle, and pipette off 20 c.c. of the aqueous portion. 

 Titrate at 100 C. plus phth. with N/2 NaOH, until a faint 



