ANALYSIS OF BUTTER-FAT. 63 



care be taken. As filtration cannot under any circumstances 

 be avoided, we think it is easier and quicker to wash on the 

 filter. Trivial as these points are, and without bearing on 

 the general question, they have been lately so much enlarged 

 upon that some mention in this place seems necessary. 



From the percentage of the insoluble fatty acids, whether 

 obtained by filter or flask washing, it is easy to draw con- 

 clusions as to the genuineness or otherwise of any given 

 sample of butter. If the quantity of fatty acid be lower than 

 88 per cent., the butter must be declared to be genuine, 

 although, as we have explained on page 49, some foreign fat 

 may be present in small amount, since good butter, with a low 

 percentage of fatty acids, bears the addition of about 15 per 

 cent, of foreign fat to raise it to the highest limit. If, how- 

 ever, the fatty acids are higher than 88 '5 per cent., we conclude 

 that adulteration has taken place, and from the difference 

 between the amount of fatty acids in butter-fat, and in other 

 fats, the addition is calculated. But whilst a butter of 

 88 '5 per cent, is passed as genuine, we base the calculation, in 

 case sophistication is proved beyond doubt, upon a lower 

 figure, namely, 8 7 '5 (following in this respect the plan 

 recommended by Dr. Muter), assuming that the original 

 butter was of average composition, and not exceptionally rich 

 in fixed fatty acids. The analyst may find it convenient in 

 such cases both to state the minimum percentage of adulte- 

 ration and the amount of foreign fat, which must have been 

 added to butter of average composition. This is done in the 

 case of milk, and the calculation in the case of butter is 

 entirely similar. An adulteration of 100 per cent., i.e., the 

 substitution of any foreign fat for butter would raise the 

 normal amount of fatty acids by 8 per cent. Let a be the 

 percentage of fatty acids found, then the amount of adultera- 



