DAIRY PRODUCTS. 85 



ESTIMATION OF FAT. 



Gravimetric. The percentage of fat in milk is the best criterion of its 

 purity, although it is not impossible to make an emulsion with an added 

 fat or oil after the natural fat of a milk has been removed. 



For determining the quantity of fat in a milk by weight it is neces- 

 sary to evaporate the sample to dryness and dissolve the fat by ether 

 or a light petroleum. 



Since, if the milk be evaporated in bulk, portions ol the fat will be oc- 

 cluded by the other solids, it is necessary, in order to secure a total solu- 

 tion of the fat, to distribute it over some inert substances. Those 

 already mentioned used for determining water, may also be employed for 

 the fat analyses. 



We use thin glass dishes (schalchen), in which the milk ik dried in a 

 thin film, or on sand, gypsum, or asbestos. The dish and its contents 

 are then rubbed up in a mortar and transferred to a continuous extrac- 

 tion apparatus. The one employed is a modification of the continuous 

 extractor made by Mr. A. E. Knorr, in which the return siphon is 

 placed wholly within the extraction tubes, thus making the apparatus 

 more compact and less liable to get broken. 



The different methods of manipulation heretofore employed for the 

 gravimetric determination are so well known that I will not describe 

 them further, but pass at once to the consideration of a new process, 

 which I have already tried sufficiently to show its merits over all others. 



ADAMS'S METHOD. 



Adams's method of estimating fat in milk 1 differs from the ordinary 

 gravimetric methods solely in the preparation of the fat for extraction. 

 Instead of drying the fat in the usual way the milk is absorbed by 

 bibulous paper. It is unnecessary to state that this paper must first be 

 thoroughly exhausted by the solvent which is used to dissolve the fat. 



The kind of paper and the method of using it first proposed by 

 Adams, are as follows : 



As for material, the only extra article is some stout white blotting-paper, known 

 in the trade as " white demy blotting mill 428," weighing 38 pounds per ream. This 

 should bo in unfolded sheets, machine-cut into strips 2$ i nches wide and 22 inches 

 long ; each sheet in this manner cuts into seven strips. 



I have tried other papers, but none have answered so well as this; it is very porous 

 and just thick enough. Each of these strips is carefully rolled into a helical coil, for 

 which purpose I use a little machine, made by myself, consisting of a stout double 

 wire, cranked twice at right angles, and mounted in a simple frame. One end of the 

 strip being thrust between the two wires, the handle is turned, and the coil made 

 with great facility. This may be done, for the nonce, on a glass rod, the size of a 

 cedar pencil. Two points have to be carefully attended to : the paper must not be 

 broken, and the coil must be somewhat loose, the finished diameter being a little 

 under an inch. I am in the habit of rolling up a considerable number at a time and 



Analyst., 1885, pp. 46 et seq. 



