54 ANALYSIS AND ADULTERATIONS OP BUTTER. 



trifling, and amounted in two experiments we made to only 

 0-0008 and 0-0016 gramme. 



The fatty acids which, are now upon the filter are well and 

 thoroughly washed with boiling water. It is quite easy to 

 whirl them round on the filter, and to incorporate them most 

 intimately with the water. The filter must never be more 

 than at most three-quarters filled. It is a good plan when 

 making the first fold in the paper to bring the edges not 

 quite even, and to double with the lower fold inside, so that 

 the capillary tube which is formed by the inside crease shall 

 not quite reach the top of the filter when placed in the 

 funnel. By this means, if any of the oily fat rises, as it 

 sometimes does by capillary attraction, it will not pass over. 

 From 700 to 1,000 c.c. of boiling water are mostly required 

 to remove all soluble acid from the oil, it being indispensably 

 necessary to wash until delicate litmus tincture is no longer 

 reddened by a few cubic centimetres of the filtrate, which 

 ought never to be less than the smaller quantity named, if 

 three grammes of butter-fat be taken. 



All water is allowed to run out of the funnel, which 

 thus retains only the fatty acids in a melted condition. The 

 funnel is then plunged into a beaker filled with cold water, 

 so that the levels of the fat inside and the water outside the 

 funnel are the same, and when the fatty acids are quite solidi- 

 fied the filter is carefully taken out of the funnel, loosely 

 stood upright in the small weighed beaker, and dried in the 

 water oven. After two hours' drying the weight is taken 

 for the first, and after two and a half hours for the second 

 time, when it mostly will be found to have remained con- 

 stant. If not, the fat must be dried for a further period, 

 until the two last weighings agree to within one or two milli- 

 grammes. The quantity on the percentage of the insoluble 

 fatty acids is thus arrived at. 



Should it, from any cause, be found necessary to interrupt 



