236 THE CHEMICAL CONTROL OF THE DAIRY. 



end into the liquid, and fill it by exhausting tlie air with the 

 mouth, then remove the lips and quickly close the upper end 

 by means of the first finger. The pipette is then removed from 

 the liquid, and by raising the first finger slightly, so much of 

 the contents are allowed to escape, drop by drop, until the lowest 

 point of the curve forming the surface of the liquid coincides 

 "with the mark on the upper part of the instrument. The con- 

 tents are then discharged, the pipette being allowed to run 

 out. 



Insert the corks, slightly damping them at the ends if neces- 

 sary ; place the hand over the corks and shake with an up and 

 down motion until the curd is dissolved ; invert the stand to 

 allow the acid in the lower bulb to mix with the rest, and 

 thoroughly mix the contents by inverting three or four times. 

 Take the bottles out of the stand one by one and allow the con- 

 tents to run into the larger portion, push up the cork, if necessary, 

 so that the graduated neck is full, and place the bottles in the cups 

 of the machine, screw on the cover and spin it for two or three 

 minutes. Place a Bunsen burner, with a flame just high enough 

 to touch the bottom of the disc-plate, underneath to prevent 

 ■cooling, unless the machine is fitted with a^ steam turbine, or 

 with one of Gerber's heaters, which will keep it at the neces- 

 sary temperature. If the fat is not in a clear limpid layer in 

 the neck, or if the upper portion is frothy, the rotation has not 

 been sufficient and must be repeated. After taking out the 

 bottles, Gerber directs that they be placed in the water-bath 

 for about a minute, which must be kept at a temperature of from 

 60° to 70° C. ; they are then ready for reading. The water-bath 

 may, without sacrificing accuracy, be dispensed with if the disc 

 is kept warm. It is an advantage to use a flame, as the corks 

 have a tendency to come out in the bath, thereby spoiling the 

 estimation. 



Reading the Fatty Layer. — Hold the butjTometer up to the 

 light, and by slight pressure on the cork adjust the bottom layer 

 to one of the larger lines on the scale ; count up the number of 

 divisions between this and the lowest curved fine at the top ; 

 each of the larger divisions is equal to 1 per cent, of fat, and 

 the smaller j^„ per cent, of fat ; every fifth smaller division is 

 also made somewhat longer to facilitate reading. In the illus- 

 tration (p. 226) the percentage of fat shown is 3-6 ; observe that 

 the lower layer is coincident with one of the longer lines, and 

 that the lower curved line at the top is thirty-six smaller 

 divisions above that. 



All pipettes are graduated to run out ; therefore the liquids 

 must not be blown out. 



Separated milks require to be whirled for a somewhat longer 



