48 MILK ANALYSIS 



the mixture whirled, and the fat measured. The percentage 

 of fat will be that based on the 25 c.c. used, and the amount in 

 the original sample may be calculated from the dilution. 



Cochran's method. — This is based on the solution of the curd 

 by the DeLaval method and solution of the fat in ether. It may 

 be applied by means of the L-B. bottles and centrifuge, or with 

 a special flask (which does not require a centrifuge) devised by 

 Cochran. If L-B. bottles are used, the reading must be multi- 

 plied by 3, since only 5 c.c. of the sample are taken. The pro- 

 cess is especially adapted to sweetened condensed milk and 

 cereal foods containing fat. The fat of normal cereals can be 

 accurately determined by it. The curd is dissolved by a mixture 

 of equal parts sulfuric acid and 80 per cent, acetic acid. This 

 mixture may be made beforehand or the acids may be added 

 in succession to the material in the bottle or flask. With the 

 flask, all materials must be added through the side-tube. 



Ordinary milk is taken undiluted, but condensed milk is 

 diluted. Sweetened condensed milk is diluted with 3 times its 

 weight of water; unsweetened condensed with an equal weight 

 of water. 



5 c.c. of the prepared sample are introduced into the flask 

 by means of the side-tube, 5 c.c. of the acid mixture added slowly 

 with shaking, taking care that the liquid does not get into the 

 graduated tube. If the liquid becomes dark brown and free 

 from lumps of undissolved curd, the flask is allowed to cool and 

 4 c.c. of ether added (common ether will answer). If the mix- 

 ture produced by the acid is lumpy, the flask is set in tepid 

 water, heated gradually (not above 80°) and shaken gently until 

 all flocculent matter is dissolved. Care must be taken not to 

 continue this heating until masses of caramel are formed, as 

 this will prevent correct results being obtained. 



When the flocculent matter has disappeared (the liquid will 

 in any case show some turbidity from the emulsion of fat), the 

 flask is cooled and ether added as noted above. The flask is 



