CHAPTER XVII. 



THE CHEMICAL ANALYSIS OF BUTTER FAT. 



Estimation of Saponiflcation Equivalent, or alkali neces- 

 sary for complete saponification. 



Kcettstorfer's Method. Koettstorfer proposed utilising the 

 fact that butter required a greater amount of alkali for its com- 

 plete saponification than most other fats to detect adulteration. 



The method is performed as follows : A standard alcoholic 

 solution of sodium hydroxide is prepared by dissolving 25 c.c. of 

 the 50 per cent, solution of caustic soda recommended by Wollny 

 (p. 244) in 1 litre of strong alcohol ; after a day's repose, during 

 which a little salt settles out, the solution is clear and fit for use. 

 This solution, which should be approximately semi-normal is 

 standardised against semi-normal hydrochloric acid. About 

 2 grammes of the fat are weighed out into a small flask, 25 c.c. 

 of the alcoholic soda solution run in from a pipette, the flask 

 connected with an inverted condenser, and the contents gently 

 boiled for fifteen minutes. During the boiling the alcoholic soda 

 solution is standardised; 25 c.c. of the solution are measured 

 from the same pipette, which is allowed to drain for the same 

 length of time as before, and titrated with semi-normal hydro- 

 chloric acid a little phenolphthalein being added as indicator. 

 The number of cubic centimetres of hydrochloric acid solution 

 should be noted. It is advisable to perform this operation in 

 duplicate. The flask containing the saponified fat is discon- 

 nected from the condenser, a few drops of phenol-phthalein 

 solution added, and the liquid titrated with semi-normal hydro- 

 chloric acid till the pink colour just disappears. The number of 

 cubic centimetres used, subtracted from the number required by 

 the 25 c.c. of soda solution alone, will give the equivalent of the 

 alkali required for saponification; this, multiplied by 0-02805, 

 will give the weight of alkali calculated as potassium hydroxide, 

 KOH ; and the figure thus obtained multiplied by 1,000 and 

 divided by the weight of fat taken will express the " potash 

 absorption " as milligrammes of KOH per gramme of fat. It is 

 also advisable to calculate the " saponification equivalent " (a 

 term due to Allen), which is really an expression of the mean 

 molecular weight. This is calculated from the number of cubic 



254 



