116 THE ESTIMATION OF FAT. 



As originally designed, the method was as follows : Strips of 

 white blotting-paper, " mill 428," 2J inches wide by 22 inches 

 long, were coiled up loosely and held by having a brass ring 

 slipped over them. These were dried at 100 C. to constant 

 weight, the weighings being performed in a weighing bottle to 

 prevent absorption of moisture from the atmosphere. Five c.c. 

 of milk was pipetted out into a small beaker and the weight 

 noted ; one of the coils was dropped in and the milk absorbed as 

 completely as possible by the blotting-paper. When absorption 

 was complete, the coil was carefully removed and placed, dry end 

 downwards, on a glass plate, the beaker being again weighed 

 and the quantity of milk taken up by the coil found from the 

 difference of the two weights. The coil was transferred to a 

 drying oven at 100 C., and left therein till it ceased to lose 

 weight. The original method was thus available for the deter- 

 mination of total solids as well as of fat. The dry coil was 

 placed in a Soxhlet extractor* (Fig. 11), and the fat separated 

 from the solids not fat by ether. The total extract, after evapor- 

 ation of the ether and drying at 100 C., was regarded as fat. 



Allen and Chattaway modified this method by rolling up a 

 piece of string with the coil, to keep the layers of paper from 

 touching each other ; they also wrapped a piece of filter paper 

 around it, in order that no milk might escape when a weighed 

 quantity was poured thereon. 



Thompson also modified it by hanging up a strip by one end 

 and running the milk on to it from a pipette, afterwards noting 

 the weight of milk delivered by the pipette. He preferred the 

 use of filter paper instead of the blotting-paper recommended by 

 Adams. 



Vieth, immediately after the publication of the method, sub- 

 jected it to an exhaustive test, and criticised it somewhat severely. 

 He showed that blotting-paper contained matter soluble in ether, 

 and that, as Adams had ignored this, the fat estimations made 

 by Adams were too high ; he also showed that the substance in 

 filter paper soluble in ether was extracted with comparative 

 slowness by this solvent. Faber later showed the same thing. 



Disregarding these criticisms, the Milk Committee appointed 

 by the Society of Public Analysts recommended its adoption 

 by their members ; it was indeed recommended that the 

 papers should be previously extracted, but nothing was said 

 of the difficulty of removing the matter soluble in ether com- 

 pletely, it being implied that twelve siphonings were sufficient to 

 effect this. The recommendation of the Milk Committee was 



* The Soxhlet extractor was really devised by Szombathy ; it was 

 described by Soxhlet, and due credit was given by him to the inventor. 

 The apparatus is, however, always known by Soxhlet's name. 



