306 METHODS OF ANALYSIS [Chap. 



mixing the 2 solutions in this proportion, a total volume of 10161 cc is obtained, 

 containing 135.3 grams of iodin. In order to reduce this solution to the proper 

 strength (13.2 grams iodin per liter), 10.161X13.2 = 134.1; 135.3- 134.1 = 1.2] 



1 2 X 1000 

 of iodin present in excess, or — = 91 cc. of acetic acid which must be added. 



The other reagents used are described under 15. 



18 DETERMINATION. 



Weigh about 0.500 gram of fat, or 0.250 gram of oil (0.100-0.200 gram in the case 

 of drying oils which have a very high absorbent power), into a 500 cc. glass-stoppered 

 flask or bottle. Dissolve the fat, or oil, in 10 cc. of chloroform, add 25 cc. of the 

 Hanus iodin solution and allow to stand for 30 minutes, shaking occasionally, 

 The excess of iodin should be at least 60% of the amount added. Add 10 cc. of the 

 15% potassium iodid solution and continue as directed under 16. 



SAPONIFICATION NUMBER (KOETTSTORFER NUMBER).-OFFICIAL. 



1 REAGENTS. 



(a) N 1% hydrochloric acid. — Prepare as directed under I, 16 (a). 



(b) Alcoholic potassium hijdroxid solution. — Dissolve 40 grams of the purest 

 potassium hydroxid in 1 liter of 95% redistilled alcohol by volume. The alcohol 

 should be redistilled from potassium hydroxid over which it has been standing for 

 some time, or with which it has been boiled for some time using a reflux condenser. 

 The solution must be clear and the potassium hydroxid free from carbonates. 



20 DETERMINATION. 



Weigh accurately about 5 grams of the filtered sample into a 250-300 cc. Erlen- 

 meyer flask. Pipette 50 cc. of the alcoholic potassium hydro.xid solution into the 

 flask, allowing the pipette to drain for a definite time. Connect the flask with an 

 air condenser and boil until the fat is completely saponified (about 30 minutes). 

 Cool and titrate with the N/2 hydrochloric acid, using phenolphthalein as an indi- 

 cator. Calculate the Koettstorfer number (mg. of potassium hydroxid required to 

 saponify 1 gram of fat). Conduct 2 or 3 blank determinations, using the same 

 pipette and draining for the same length of time as above. 



21 SOLUBLE ACIDS.-OFFICIAL. 



Place the flask, used in 20, on a water bath and evaporate the alcohol. Add such 

 an amount of N/2 hydrochloric acid that its volume plus the amount used in titrat- 

 ing for the saponification number will be 1 cc. in excess of the amount required to 

 neutralize the 50 cc. of the alcoholic potassium hydroxid solution added, and place 

 on the steam bath until the separated fatty acids form a clear layer on the upper 

 surface of the liquid. Fill to the neck with hot water and cool in ice water until 

 the cake of fatty acids is thoroughly hardened. Pour the liquid contents of the 

 flask through a filter into a liter flask. Fill the flask again with hot water, set on 

 the steam bath until the fatty acids collect at the surface, cool by immersing in ice 

 water, and again filter the liquid into the liter flask. Repeat this treatment with 

 hot water 3 times, cooling and collecting the washings in the liter flask after each 

 treatment. Titrate the combined washings with N/10 alkali, using phenolphthalein 

 as an indicator. Subtract 5 (corresponding to the excess of 1 cc. of N/2 acid) from 

 the number of cc. of N/10 alkali used and multiply by 0.0088 to obtain the weight 

 of soluble acids as butyric acid. Calculate the percentage of soluble acids. 



