244 PHYSIOLOGICAL CHEMISTRY 



a tall 150-200 c.c. beaker. 1 The thin layer of ether which remains is diluted with 

 5 c.c. of ether, the tube slightly agitated, and the ether blown off. This is done 

 in all five times, care being taken each time to wash down the sides of the cylinder. 

 The stopper should also be washed. 



Twenty c.c. of ether are again added, and the cylinder shaken for five minutes 

 and set aside. When the ether has nearly stratified, blow it off and wash as 

 before. During the second washing stratification will complete itself. 



Evaporate the ether 2 until no trace of the alcohol, which has been carried 

 over with it, remains. To the residue add 30 c.c. of low-boiling petroleum ether 

 (should boil below 6oC.), and allow to stand over night. Petroleum for this 

 work should be frequently tested for a residue on evaporation. If a residue is 

 left, the ether should be redistilled. 



Filter the petroleum ether solution of the fat, catch the filtrate and washings 

 in a tall, weighed, 100 c.c. beaker, evaporate off the solvent, dry the beaker at 

 90C., desiccate and weigh. 



After weighing, dissolve the contents of the beaker hi 50 c.c. of benzol, heat 

 almost to the boiling-point, add 2 drops of a 0.5 per cent solution of phenolphthalein, 

 and titrate with a decinormal solution of sodium alcoholate. 3 



Calculations. The weight of total fat is obtained by subtracting the 

 weight of the empty beaker from the weight of the beaker plus the dried 

 fat. The weight of fatty acids (in terms of milligrams of stearic acid) 

 is obtained by multiplying the number of cubic centimeters of deci- 

 normal sodium alcoholate solution by the factor 28.4. The difference 

 between the weight of total fat and the weight of fatty acids is the 

 weight of neutral fat in the sample extracted. 



A separate determination without the addition of hydrochloric acid 

 may be run upon the sample, for the purpose of determining the weight 

 of neutral fat and free fatty acids. The difference between this weight 

 and the weight of total fat is the weight of fatty acid present in the 

 original sample in the form of soaps. 



1 This is accomplished in the same manner that water is blown from a wash bottle. 

 The submerged end of the delivery tube is bent upward, as in the apparatus used for the 

 determination of fat in milk by Meig's method (see Milk). This avoids upward currents 

 which would disturb the subjacent alcohol-ether-feces layer. 



2 Erlenmeyer flasks of about 200 c.c. capacity may be used, instead of beakers, for the 

 collection of the ether blown from the cylinders. The ether may then be distilled and re- 

 covered. The same procedure may be followed in removing the petroleum ether. 



3 In the preparation of the sodium alcoholate solution, absolute alcohol and freshly cut, 

 bright, metallic sodium are used; otherwise the procedure is the same as that for the stand- 

 ardization and preparation of any alkali solution. 



