58 



FOODS AND FOOD ADULTERANTS. 



the elbow and filled with broken glass or glass wool. After the soap 

 solution has been transferred to this flask, the evaporating dish is rinsed 

 out with 25cc. more water, which is added to the contents of the llask, 

 and the fatty acids are then set free by the addition of 20cc. of a solution 

 of phosphoric acid, 1 making- the liquid measure in all about TOcc. Heat 

 is applied gently at first, and gradually increased until the distillate 

 comes over regularly. When 50cc. have distilled off the operation is 

 finished and the distillate is titrated with one-tenth alkali, using phenol- 

 phthalein as an indicator. 



I have adopted phosphoric acid in preference to sulphuric for setting 

 free the fatty acids, because ifc is not so liable to carry over as the hit- 

 ter; much greater care is necessary when sulphuric acid is used. Be- 

 fore the modification of the delivery tube was adopted, I frequently 

 found H 2 SO 4 in the distillate. Thus, before using the bulb, two blank 

 experiments required 1.8 to2.0ec., one-tenth alkali, for neutralization and 

 gave a perceptible precipitate of BaS0 4 . After adding the bulb I found 

 blanks occasionally to require as much as .Sec. when the distillation had 

 not been carefully watched. The following comparative results show 

 that there is practically no difference which acid is used, when the 

 operation is carried on with care. The processes used were identical, 

 except that in the second, 20cc. of 10 per cent, sulphuric acid was substi- 

 tuted for the phosphoric acid. The results arc for 2.5 grams of fat. 



Blanks should always bo run, and will be generally found to require 

 .1 to .3cc. of the deci-normal soda before they will show the color with 

 the phenol indicator. 



Koettstorfer^s process 2 (as used in this laboraiory}. Anout 2.5 grams 

 butter fat (filtered and free from water) are weighed into a patent rubber- 

 stoppered bottle and 2jcc. (approximately) semi normal alcoholic potash 

 added. The exact amount taken is determined by weighing a small 

 pipette with the beaker of fat, running the fat into the bottle from the 

 pipette and weighing beaker and pipette again. The alcoholic potash 

 is measured always in the same pipette and uniformity further insured 

 by always allowing it to drain the same length of time (thirty seconds). 

 The bottle is then placed in the steam bath together with a blank, con- 

 taining no fat. After sapouification is complete, and the bottles cooled 

 down, the contents are titrated with accurately semi-normal hydro- 



1 Made by dissolving 200 grams of commercial glacial phosphoric acid in a litre of 

 (vatcr; its specific gravity is 1.140. 



2 Zcit. Anal. Chem*. 1879, p. 199 ; Analyst, 1879, p. 100. 



