1 82 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



5 gm. of the fat are weighed out into a flask with a flat bottom of 

 about 250 c.c. capacity and with a neck 2 cm. wide and 7-8 cm. long. 2 c.c. 

 of a solution of 98 per cent, caustic soda in an equal weight of water, 

 which is protected from carbonic acid, and 10 c.c. of 92 per cent, alcohol are 

 added. The contents are heated on a water-bath under a reflux condenser 

 for 15 minutes; the alcohol is removed by warming the flask for about 30 

 minutes without a condenser ; 100 c.c. of boiling water, freed from carbon 

 dioxide by boiling for at least 10 minutes, are added and the soap dissolved. 

 The flask is connected to a condenser by a bent tube 7 rnm. in diameter and 

 15 cm. in length from the cork of the flask. The condenser is 8 mm. in 

 diameter and 35 cm. long. The contents of the flask are acidified with 40 

 c.c. of N sulphuric acid, a piece of porcelain added, and distilled from an 

 asbestos board 12 cm. in diameter containing an opening 5 cm. in diameter. 

 The heating is begun cautiously so as to melt the fatty acids and then at such 

 a rate that no c.c. distil over in about 30 minutes. The distillate is collected 

 in a measuring flask of 1 10 c.c. capacity. The distillate is mixed and 100 c.c. 

 are titrated with 'iN alkali using 0*5 c.c. of i percent, phenolphthalein solu- 

 tion as indicator. 



Determination of the Hehner Value. 



3-4 gm. of the fat are weighed out in a porcelain basin 13 cm. in 

 diameter; 50 c.c. of alcohol and 1-2 gm. of potassium hydroxide are 

 added. The mixture is heated on a water-bath with constant stirring till 

 saponification is complete and until a clear solution is obtained. If a drop of 

 water be added and no turbidity be produced, the saponification is complete. 

 The solution is evaporated till it becomes pasty and 100 to 150 c.c. of water 

 are added. It is acidified with sulphuric acid and warmed till the fatty acids 

 form an oily layer on the surface. The fatty acids are filtered off on to a 

 weighed filtered paper 10 cm. in diameter. This should have a texture so 

 that it prevents fatty acid from passing through it and it is half filled with hot 

 water and kept at this level with hot water during the filtration. The fatty 

 acids are washed till the washings no longer react acid. The filter and its 

 contents are dried at 100 for two hours, cooled and weighed. 



Determination of the Acetyl Value. 



10 gm. of the fat are boiled with twice the weight of acetic anhydride in 

 a round flask under a reflux air condenser for two hours. The solution is 

 poured into about 500 c.c. of hot water contained in a beaker and boiled for 

 half an hour, whilst a slow current of carbon dioxide is passed through it to 

 prevent bumping. On standing it separates into two layers ; the aqueous layer 

 is syphoned off and the remaining oil washed three times with water, so as 

 to remove acetic acid, which may be tested for by its acid reaction. The 

 acetylated fat is collected on a filter paper and dried at 100. 



2-5 gm. of the acetylated product are saponified with -iN alcoholic 

 potash as described under determination of the saponification value. The 

 solution is evaporated to expel the alcohol and the residue dissolved in water. 

 The same volume of *iN acid as of alkali used in the saponification is added 

 and the solution warmed. The aqueous solution is syphoned off through a wet 

 filter and the fatty acids washed with hot water till all the acid is removed. 

 The filtrate and washings are titrated with 'iN alkali using phenolphthalein 

 as indicator. Soluble fatty acids, if present in the fat, must be separately 

 determined in the same way and their amount deducted from the value 

 obtained. 



