ANALYSIS OF BUTTER-FAT. 55 



the analysis, whilst the fat is still on the filter and not per- 

 fectly washed, the funnel should be plunged into water as 

 described, keeping the filter-paper moist. No loss of fatty 

 acids need then be apprehended. 



In case the washing of the fatty acids be not continued 

 sufficiently far, the drying to constant weight proceeds after- 

 wards considerably slower than it does in a properly executed 

 experiment ; it may stretch over a period of many hours, 

 during which some change of the fatty acids by oxidation 

 may be incurred. This is doubtless due to the presence of 

 caproic and similar acids in butter, which, being only very 

 sparingly soluble in even boiling water, are obstinately re- 

 tained by the insoluble fatty acids, and if not removed by 

 washing, they are slowly volatilised at the boiling point of 

 water. 



If a few drops of water should happen to have remained 

 in the filter when removed to the weighed beaker, they will 

 sometimes collect on heating below the melted fat, and vola- 

 tilise but exceedingly slow. In such eases it is best to follow 

 the advice of Dr. Muter, and to add a drop or two of alcohol, 

 when the removal of the water proceeds without difficulty. 



The following may be taken as an instance of the determi- 

 nation of the insoluble fatty acids in genuine butter-fat : 



Beaker and butter-fat 39'3226 



Beaker 36-0395 



Butter-fat taken 3 '283 1 



Tube and filter 15-4281 



Tube empty 14*8451 



Filter 0-5830 



Beaker empty 20-9967 



Beaker and filter ... 21-5797 



