ii BUTTER 153 



in milligrams, per 1 gram butter fat. A blank experiment must 

 be made alongside each determination. 



For butter fat the Koettstorfer number generally lies between 

 220-5 and 232'0. 



III. THE HEHNER NUMBER. 



By the Hehner Number 1 is understood the amount of in- 

 soluble fatty acids which is obtained from 100 parts of fat. 



Three to four g. of pure butter fat are weighed out into a 

 porcelain dish of about 10 cm. diameter, and saponified with 

 1-2 g. of caustic soda in 50 c.c. alcohol, the dish being warmed on 

 the water-bath and the contents well stirred. The solution of soap 

 is evaporated to a thick syrup, then dissolved in water, and the 

 soap decomposed by adding dilute sulphuric or hydrochloric 

 acid until the reaction is strongly acid. The liquid is then 

 heated until the fatty acids have collected as a clear oil on the 

 surface, and then poured on to a dried and weighed filter made 

 from very thick paper. Before using the filter it should be half 

 filled with warm water, for this prevents the filtrate from being 

 turbid. The fatty acids remaining on the filter are washed with 

 small quantities of boiling water, the liquid not being allowed 

 to fill the filter more than two-thirds full. When the wash- 

 water measures two litres the washing is discontinued, and the 

 fatty acids are allowed to solidify. Finally the filter and the 

 fatty acids are placed in a weighed glass beaker and dried in 

 the oven at 100 C. The amount of fatty acids is then 

 calculated for 100 parts of fat. 



The Hehner number for pure butter fat varies between 85 '4 

 per cent, and 91'30 ; the average may be taken as 87 '5 per cent. 



IV. THE IODINE NUMBER. 



As is well known, certain unsaturated fatty acids (oleic, 

 hnoleic, &c.) form addition compounds with iodine, 1 mol. oleic 

 acid (which is a component of butter fat), for example, taking 

 up two atoms of iodine. 



The iodine number of a fat is therefore understood to be the 

 amount of iodine, expressed as percentage of fat, which the 



1 Zeitschrift fur analyt. Chemie, 1877, Vol. XVI, p. 145. 



