ii BUTTER 161 



In Balers' special thermometer (Fig. 63), the left-hand side 

 of the scale gives the figures in black for summer butter (S), 

 and the right-hand side for winter butter ( W). The scale for 

 pigs' fat is on the right and in red figures. 



It must not be forgotten that the critical line for natural 

 butter is colourless on the refractometer scale, whilst that for 

 margarine is blue, owing to the greater dispersive power of 

 natural butter. Fat, which has a less dispersive power than 

 butter, shows a red critical line on the refractometer. 



2. The Crismer Number. 



Whilst the critical temperature of solution of butter-fat in 

 alcohol varies on an average between 53 and 57, as has already 

 been seen (p. 145), the temperature in the case of margarine fat 

 is fT -^ . An addition of margarine to natural butter may 

 therefore be recognised by the raising of the Crismer number. 

 There are, however, cases in which natural butter possesses an 

 abnormally high Crismer number, so that great difficulty often 

 arises in deciding whether adulteration with margarine has 

 taken place, especially if the quantity added is only small. 



3. The Reichert-Meissl Number. 



Pure butter-fat has on an average a Reichert-Meissl number 

 of 24-34, whilst that of the fat used in the manufacture of 

 margarine is only G'l-0'9. In the process of manufacture these 

 last figures may be raised to between 1 and 2. The difference 

 then between the Reichert-Meissl number of butter and that of 

 margarine is considerable, and so it might be thought that this 

 method would serve to detect quite small adulterations with 

 margarine. It is, however, not to be forgotten that the volatile 

 fatty acids present in butter may vary considerably owing to a 

 number of causes, one of the chief of which is the individuality 

 of the cow. Butter made from the milk of a single cow some- 

 times gives a very low Reichert-Meissl number, even as low 

 as 13-14. 



Further, the percentage of volatile fatty acids varies with 

 the period of lactation, so that the Reichert-Meissl number is 

 at its highest a few days after calving, and shortly afterwards 



M 



