FOODS 89 



heating for half an hour, or until the soap is dry. This is 

 to get rid of the alcohol. Freshly boiled aq. dest. is 

 added cautiously, while still hot, to the amount of TOO c.c., 

 and the flask carefully heated until the soap is dissolved. 

 Thereafter, 40 c.c. of N/i H 2 SO 4 are added, and 3 to 4 

 pieces of pumice stone, and the flask is rapidly connected 

 to a condenser by a tube having a bulb. Heat at first with 

 a small flame to melt the insoluble fatty acids (liberated 

 with the soluble fatty acids by the action of the sulphuric 

 acid), but do not boil. When fusion is complete, increase 

 the heat, and distil over no c.c. in thirty minutes. Shake 

 the distillate, filter 100 c.c., add 0-5 c.c. of i per cent 

 phenolphthalein solution, and titrate with N/io soda or 

 baryta. The number of c.c. used X i-i is called the 

 Reichert-Wollny number, and for genuine butter varies 

 from 24 to 32. A blank experiment, using the reagents 

 alone, supplies a correction for any acidity due to these. 



This is an official process, recognized by the Government 

 Laboratory and the Society of Public Analysts. Sundry 

 details are given in the official description, such as the 

 length of neck of flask, size of tubes and condenser, etc., 

 all to secure uniformity of method and apparatus and so 

 give comparable results. When the Reichert-Wollny figure 

 has been got, if it is 24 or above, the sample is looked 

 upon as genuine, and as i c.c. N/io soda = 0-0088 grm., 

 or 8-8 mgr. of butyric acid, the percentage of soluble volatile 

 fatty acids returned as butyric acid is easily calculated. 

 With the Reichert-Wollny varying from 24 to 32, the per- 

 centage of acid will vary from 4-2 per cent to 5-6 per cent. 



Pure Margarine Fats give a Reichert-Wollny figure of 

 0-2 to i per cent. As a maximum of 10 per cent of butter- 

 fat is allowed to be added for flavouring purposes, the 

 maximum Reichert-Wollny figure for a saleable margarine 

 will be i + 10 per cent of 32 (= 3-2), or 4-2. The figure 

 usually taken is 3. If a butter gives a Reichert-Wollny 

 of say y, let x stand for the percentage of margarine, 

 then 3 x x + 24 (ioo-#) = y x 100 ; or x = (2400 -looy) 



-f- 21. 



Unfortunately for the value of this process, vegetable 

 fats which give a moderate Reichert-Wollny figure are now 

 being used for food. Thus coco-nut oil has a Reichert- 



