150 VOLUMETRIC AND INDIRECT ESTIMATION OF FAT. 



notch to restore equilibrium, the smaller should be hung from 

 the upturned enc 1 of the larger. 



The use of this balance, though convenient when many samples 

 are being tested, is not necessary, as the weighings may be made, 

 but slightly less expeditiously, with an ordinary balance. 



Stokes' Modification. Stokes employs a modification of the 

 acido-butyrometer ; it is open at both ends, one being provided 

 with an indiarubber washer kept in place by a screw cap, while 

 the other can be closed with a cork. It is placed screw cap 

 downwards : up to the zero mark of the graduations, the tube 

 holds 1-5 c.c., and the neck is graduated to read percentages of 

 fat ; the upper portion consists of two bulbs ; from the zero mark 

 of the graduations up to a mark between the two bulbs the 

 bottle holds 13-5 c.c., while from this mark to a mark above the 

 second bulb the capacity is 15 c.c. 



It may be used without a centrifugal machine as follows : 

 1*5 c.c. of amyl alcohol are poured in to the zero mark, or, better, 

 measured by means of a pipette provided with a rubber teat of 

 about 1*5 c.c. capacity; sulphuric acid is poured in carefully 

 to the mark between the bulbs, and then the milk to be tested 

 is poured in to the upper mark. An indiarubber cork is put 

 into the upper opening, and the contents of the butyrometer 

 mixed well by shaking and inversion. The tube is now stood, 

 cork downwards, in hot water, the screw cap loosened, and 

 left for an hour ; the fat will have collected in a layer in the 

 graduated neck, and can be read off in the same manner as 

 previously described. 



This forms an extremely cheap method of estimating fat in 

 milk, with an accuracy quite sufficient for most purposes, and 

 can be recommended where only one or two samples per day 

 are to be tested. 



The apparatus can be used also for the more exact estimation 

 of fat by measuring the milk, acid, and amyl alcohol by means 

 of pipettes, or automatic measuring apparatus, and whirling in a 

 centrifugal machine. 



The Lister-Stokes machine is made to take these bottles : it 

 differs chiefly from the Lister-Gerber in the form of the disc. 

 Instead of having a lid, the disc is made double and open in the 

 centre, the butyrometers being slid into cardboard tubes in 

 pockets, which are symmetrically arranged, radiating from the 

 centre. This form of machine has the advantage of having the 

 pockets comparatively large, and can be used for other purposes. 

 The whole of the disc can be filled conveniently with hot water 

 should it be desirable to prevent cooling during centrifugal 

 separation. 



Alkaline Butyrometric Methods. Gerber has devised 



