1 52 MILK AND DAIRY PRODUCTS PART 



condensers adopted in the laboratories where the Dutch butter 

 supplies are tested. The Reichert-Meissl number may vary in 

 the case of pure butter fat between 19 and 34, but only in rare 

 instances does it fall below 24 (see below, under " Proof of 

 Adulteration of Butter"). 



It is to be noticed that in the determination of the Reichert- 

 Meissl number the whole of the volatile, water-soluble, fatty 

 acids in 5 g. butter fat is not obtained, but only a portion 

 (about 90 per cent.). The results, however, are constant for 

 the same sample of butter, provided that the details of the 

 method are carefully followed each time, and so the figures 

 obtained from different samples of butter fat yield numbers 

 which can be correctly compared one with another. 



II. THE KOETTSTORFER, NUMBER. 



The Koettstorfer Number l gives the number of milligrams 

 of caustic potash which are required for the saponification of 

 1 g. fat. 



The estimation is made by weighing out 1 or 2 g. of clear 

 filtered butter fat which has been well mixed into a 150 c.c. 

 round-bottomed flask of Jena glass; 25 c.c. of an alcoholic solution 

 of caustic potash, made by dissolving enough caustic potash in 

 rectified spirit to make it about seminormal, are then added. 

 The flask is closed with a cork through which a long glass tube, 

 about 75 cm. in length and 13 mm. in diameter, is passed to 

 act as an air condenser. It is preferable to choose a glass tube 

 made from Bohemian potash glass for the purpose. The flask 

 is then heated for 15 minutes on the water-bath, the contents 

 being allowed to boil gently and shaken from time to time to 

 accelerate the saponification. Whilst the contents of the flask 

 are still warm they are titrated back with N/2 hydrochloric acid, 

 a few drops of alcoholic phenolphthalein being used as indicator. 

 When the liquid becomes acid it changes suddenly to a yellow 

 colour. By deducting the amount of acid required for this last 

 titration from that which was needed to neutralise 25 c.c. of 

 the original caustic potash, the amount of caustic needed for 

 the saponification is obtained. This amount is then calculated 



1 Zeitachrift fifr analyt. Chemie, 1879, Vol. XVIII, p. 199. 



