ANALYSIS OF BUTTER-FAT. 53 



recommended for similar operations, partly because of its 

 affinity for water, partly because two niters, cut with the 

 same stamp out of the same paper, never are of equal weight, 

 but often many centigrammes different. 



The filter paper must be of the very best quality, and of 

 close texture, so as to allow even boiling water to filter only 

 drop by drop through it. Only with such paper which must, 

 moreover, be carefully adjusted to the funnel is it possible 

 to obtain a perfectly clear filtrate, free from even the minutest 

 traces of fatty matter. Through such filter paper the filtra- 

 tion is somewhat slow ; but this can only be considered an 

 advantage, as several samples may be examined at the same 

 time, whilst loose paper would both allow a small proportion 

 of the fatty acids to pass through it, and filter with such 

 rapidity that it can hardly be kept full from the wash-bottle. 

 A double filter may often be used with advantage. 



The filter being moistened and partly filled with boiling 

 water, the fatty acids and the acid liquid below these are 

 now poured upon it. As soon as all liquid has been removed 

 into the funnel, the basin is washed with boiling distilled 

 water, until every trace of oil has been transferred upon the 

 filter, the glass rod being freed from oil in a like manner. It 

 might be supposed that the fatty acids would obstinately cling 

 to the vessel, and that a loss would thus be incurred. This, 

 however, is by no means the case, for boiling water takes 

 away every trace of the fat, especially when the stream 

 of boiling water from the wash-bottle is directly turned 

 with some force upon the particles to be dislodged. Should, 

 however, any doubt arise as to whether all fat has been 

 removed from the basin and the glass rod, these may be dried 

 on the water-bath and washed with ether, the ethereal solution 

 being afterwards either evaporated in a weighed beaker, or 

 added directly to the fatty acids when taken out of the 

 funnel. The quantity thus obtained is, however, very 



