FAT CRYSTALS 



163 



Preparation of the Acetates. — A small amount (3 to s cc.) of acetic anhydrid is 

 added to the dry residue in the beaker and heated to boiling over a free flame, the 

 beaker being covered with a watch glass during the process. After a brief boiling — a 

 few seconds is sufficient — the flame is removed and the beaker transferred to the 

 steam bath and left there untU the acetic anhydrid is driven off. 



Purification of the Acetates. — Thirty-five cc. of hot 80 per cent, alcohol are 

 added to the acetylated residue in the beaker and heated to bofling with vigorous 

 stirring. The liquid is then filtered quickly through a folded filter and the in- 

 soluble residue washed well with boUing 80 per cent, alcohol. The acetates of chol- 

 esterol and phytosterol are dissolved, while the greater portion of the impurities 

 present are not dissolved by the alcohol and remain on the filter. Paraffin and paraf- 



FiG. 52. — Phytosterol crystals. 



Fig. 53. — Cholesterol crystals. 



fin oil, if present, are likewise separated by this treatment. The combined filtrate 

 and washings are next cooled to a temperature of 10° to 12° C. and allowed to stand 

 at that temperature for 2 to 3 hr. During this time the acetates of cholesterol 

 and phytosterol crystallize from the solution. They are removed by filtra- 

 tion, washed with cold 80 per cent, alcohol, and then dissolved on the filter with a 

 stream of hot absolute alcohol from a wash bottle, as little alcohol as possible being 

 used. The alcoholic solution of the acetates is caught in a small glass e\-aporating 

 dish, two or three drops of distilled water being added to the solution and heat applied 

 if it is not perfectly clear. The dish is then set out on a desk in the laboratory and the 

 alcohol allowed to evaporate spontaneously. The contents are stirred occasionally 

 and the deposit of crystals which forms around the edges of the liquid and on the sides 

 of the dish rubbed down into the solution with the stirring rod. As soon as a good 

 deposit of crystals has formed they are removed by filtering through a hardened 



