450 Conditions Affecting Butter-Fat. 



quantities of insoluble acids as may have also distilled over, and 

 the amount of the dissolved volatile acids is then determined by 

 neutralising the acid liquid with standard alkali. 



This process, in one modification or another, is variously known 

 as the Reicherty the Reichert-Meissl, or the ReicJiert- Wollny 

 method of determining the amount of volatile acids in fats. 



Before, however, any valid inference as to the amount of ad- 

 mixed margarine can be drawn from data obtained by the fore- 

 going methods, it is necessary to have precise information as to 

 the differences in these respects which genuine butter is liable to 

 exhibit under the varying conditions in which it is produced. 

 As the result of applying these tests to butter produced under 

 known conditions, it has been found that butter-fat, derived from 

 cows nearing the end of their lactation period, is invariably poor 

 in acids of low molecular weight — that is, in volatile acids. Hence 

 the butter obtained at such periods gives low Reichert- Wollny 

 figures. 



This was first clearly indicated by the late Professor L. F. 

 Nilson, of Stockholm, who some years ago {Zeitschrift fur 

 Analytische Chemic^ vol. 28) published the results of the analyses 

 of over 800 samples of butter, obtained from the milk yielded 

 by a herd of 15 cows. He found : — 



(1) . That in the fat of colostrum the proportion of volatile 

 acids is very low. 



(2) . That the amount of these acids then rapidly increases, 

 and reaches a maximum in from five to seven days after the 

 cows have calved. 



(3) . That the volatile acids then gradually diminish until the 

 close of the lactation period ; although even at the end of this 

 period the figure shown was rarely less than 26. The lowest 

 value obtained was 25. 



It has also been observed that cows exposed to cold, wet, or 

 inclement weather give butter containing a relatively small 

 proportion of butyric acid and its near homologues. Scanty 

 pasture, too, is conducive to a lowering of the amounts of the 

 volatile acids. 



The joint effect of these influences is well illustrated in the 

 character of a certain amount of Dutch butter produced during 

 the autumn — say from the latter part of September to the early 



