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ligation. When light passes from a rarer medium into one of greater optical 

 density the rays of light on entering the denser medium deviate towards the 

 normal, the ratio of this deviation from the normal for the two media is 

 constant and is called the refractive index with reference to the two media. 

 Specific Gravity. — Specific gravity expresses the ratio between masses of 

 equal volumes of a substance and that of water taken as a standard. The 

 masses of two bodies are projwrtional to their weights, the specific gravity 



of a substance can be expressed thus: Specific gravity = , where X and Y rep- 



Y 



resent the weights respectively of equal volumes of the substance and water. 



Reichert-Meissl Value. — The Reichert-Meissl value expresses the number 

 of cubic centimeters of decinormal solution of Sodium or Potassium hydrate 

 required to neutralize the volatile acids obtained from five grams of butter 

 fat by the Reichert-Meissl distillation Process. The Reichert-Meissl value 

 does not represent the absolute amount of volatile soluble acids, but only 

 indicates the relative amount of the volatile acids. 



Saponification Value. — The saponification value expresses the number of 

 miligrams of potassium hydrate reciuired to saponify one gram of fat, its 

 value depends on the molecular weight of the fattj- acids. The lower the 

 molecular weight the higher the saponification value. 



Iodine Value. — The iodine value indicates the per cent, of iodine or iodine 

 chloride absorbed by the fat. All unsaturated fatty acids have the property 

 of absorbing iodine forming .substitution compounds. In butter fats the oleic 

 acid is the only unsaturated acid. 



Insoluble Acids or Hehner Value. — This value represents the insoluble 

 acids in fats. Inasmuch as fats are composed of mixed glycerides of fattv 

 acids both soluble and insoluble, on saponification of the mixed glycerides, 

 the fatty acids form salts with the liberation of glycerol. When the salts 

 thus formed are decomposed by some mineral acid, the insoluble acids can be 

 separated from the soluble acids and the per cent, of insoluble acids is called 

 the Hehner value. 



Maumene Value. — When mixing sulphuric acid with oils the temperature 

 rises and varies with the source of the oils and their chemical composition, 

 the rise being also greater for the drying oils than for the nondrying oils. 



The rise of temperature for different oils is called the Maumene value of 

 the oils. 



Purdue University. 



