i88 



THE A L UMNl JO URN A L . 



lenta's test or the solubility in glacial 

 acetic acid distinction between glycerides 

 and hydrocarbons. The saponification 

 test is actually the most useful and gen- 

 erally applied test. The figures given 

 reading the number of milligrams of 

 alkali, usually potassium hydrate, re- 

 quired to saponify i Gram of the fat or 

 oil. 



The alkali, KOH, is usually made 

 approximately quarter or half normal, 

 and should be alcoholic in order to avoid 

 the high pressure necessary in saponify- 

 ing with aqueous solutions. 



Care must be taken in the selection of 

 the alcohol; most commercial samples 

 contain notable quantities of aldehyde 

 and acetic acid, and turn very dark in a 

 very short time. To purify alcohol the 

 Waller process may be most easily ap- 

 plied. This consists in adding small 

 quantities of finely powdered perman- 

 ganate of potassium to the sample, 

 shaking well after each addition, until 

 quite a strong permanganate color re- 

 mains, the manganese oxide is then 

 allowed to settle and the clear superna- 

 tant liquid transferred to a retort and 

 slowly distilled with the addition of 

 some small fragments of calcite. The 

 first portions of the distillate which con- 

 tain some aldehyde are set aside for 

 further treatment. Another method 

 consists in slowly distilling a mixture of 

 alcohol and free fatty acid, such as may 

 be obtained from Koettstorfer residues. 



To determine the Koettstorfer figure, 

 weigh out 2.500 Grams of the fat or oil 

 in a low wide mouth 4-oz. hard-glass 

 flask, run in 50 C. c. of the alkali from a 

 pipette, cover with a watch glass and 

 place on a boiling water bath, at the 

 same time run 50 C.c. of the alkali in a 

 similar flask, cover with a watch glass 

 and also place on a boiling water bath, 

 the boiling alkali will rapidly combine 

 with the fat, but the action is not com- 



plete until nearly all the alcohol has 

 passed ofi^. The two flasks, both blank 

 and test, should evaporate at about the 

 same rate. As they approach dryness 

 remove the watch glasses and allow the 

 last of the alcohol to pass off" rapidly ^ 

 when all is gone, add to each 100 C.c. 

 of neutral alcohol containing i C.c. of 

 phenol phtalein solution, replace the 

 watch glasses and set again on the water 

 bath, the blank should rapidly go into 

 solution leaving no residue. A turbidity 

 shows formation of carbonate, in which 

 case the test will be unreliable; if clear, 

 rapidly determine the exact strength by 

 means of normal hydrochloric acid and 

 note the result. Now remove the test 

 flask in which the saponified oil should 

 be in solution, place it on a piece of 

 white paper or tile in front of window 

 and run in normal hydrochloric acid 

 from a burette until on looking at the 

 white surface through the liquid no trace 

 of purple is seen, and the liquid begins 

 to cloud, this is the neutral point. Re- 

 cord the number of cubic centimetres of 

 acid used and subtract from the amount 

 used by the blank the difference will be 

 the number of cubic centimetres used to 

 saponify the 2. 500 grams of fat. To deter- 

 mine the exact strength of the alkali, 

 note the number of C.c. of normal acid 

 used for 50 C.c. of alkali, multiply by 

 0.0561 the value of each C c. of acid in 

 terms of KOH, and divide by 50 C.c. 

 used. 



The number of milligrams of alkali 

 used to saponify the fat, divided by 2.5 

 Grams and multiplied by 100 will give 

 the per cent, of alkali necessary for 

 saponification, this amount multiplied 

 by 10 will give the Koettstorfer figure. 



The figures obtained this way do not 

 distinguish between the glycerides or 

 true fat and the free fatty acid, for the 

 purpose of obtaining the true or ether 

 figure (Esterzahl), it will be necessary to 



