192 The Analysis of Dairy Produce [322 



Milk fat differs from all other natural fats in that it contains 

 a considerable percentage of the so-called ' lower ' fatty acids — 

 i.e., acids having a comparatively small molecular weight. 

 Many of these lower acids are volatile at the temperature of 

 boiling water, and are soluble in water. 



These three properties — i.e., low molecular weight, volatility 

 in steam, and solubility in water — are used for the detection 

 and estimation of those fats peculiar to butter. 



322. Koettstorfer's Method. — The molecular weight of 

 any acid may be determined by weighing the quantity which will 

 combine with 56 grams of KHO. As it would be unscientific 

 and inconvenient to speak of the average molecular weight of 

 the fatty acids in butter, it is usual to express this peculiar 

 property as a Koettstorfer number, which is the number of 

 milligrams of KHO which are neutralised by the fatty acids in 

 1 gram of butter fat. In this method a weighed quantity 

 of butter fat is heated with an excess of standard alcoholic 

 potash. After the reaction is complete, the excess of potash 

 is estimated by means of standard hydrochloric acid. 



The solutions required are seminormal hydrochloric acid, 

 which may be prepared by one of the methods given in Part II., 

 and alcoholic potassium hydrate. 



Alcoholic Caustic Potash. Thirty-two grams of caustic 

 potash are weighed out roughly and dissolved in a litre of 

 strong alcohol. This solution, if made from methylated spirit, 

 very rapidly discolours and alters in strength. Students are 

 advised to make up only small quantities as they may be 

 required. In laboratories where large numbers of butter 

 samples are analysed the alcohol is specially prepared. Fifty 

 grams of potash are dissolved in a ' Winchester ' of methylated 

 spirit and left to stand for at least a week. The spirit is then 

 distilled. After this treatment it may be used for making 

 solutions of caustic alkalis, which will only alter very slowly. 



