THE ANALYSIS OF MILK 19 



vertical spindle running on ball bearings. The driving 

 is performed either as in the two-bottle machine, by a 

 string wound round the spindle or by a handle. Very 

 large machines are fitted with a steam or water turbine, 

 or an electro-motor (Fig. 143), and may be provided with 

 heating apparatus to keep the disc warm while running. 



Hot-water Tank. If the disc is not kept warm while 

 running the bottles must be placed in water between 

 60 and 70 C., before reading, in a small tank. 



The Process. Place a sufficient number of bottles in 

 the stand, open end upwards, and to each add 10 c.c. 

 of sulphuric acid (see Appendix) ; add n c.c. of milk to 

 each by means of the n c.c. pipette ; then add i c.c. of 

 amyl alcohol (see Appendix). 



To measure with a pipette : place the constricted end 

 in the liquid, and draw with the mouth till the level of 

 the liquid is at least one inch above the mark on the 

 upper stem ; rapidly remove the mouth, and place the 

 forefinger over the top ; the finger must not be wet, 

 though it may with advantage be slightly damp ; if this 

 is done with sufficient rapidity, the liquid is above the 

 mark on the upper stem, if it is not it must be drawn 

 up again. Carefully and slightly raise the finger to 

 allow the liquid to run down slowly to the mark, then 

 stop the flow by pressing the finger on the top ; this^ 

 operation requires some practice, but presents no real 

 difficulty. Keeping the finger pressed down on the top, 

 lift the pipette out of the liquid, and, taking care not to 

 let any drops fall while moving, place the end of the 

 pipette inside the neck of the bottle (Fig. 15) ; hold the 

 pipette slanting, and let the point touch the side of the 

 neck. On lifting up the forefinger the contents will 

 run out down the side of the bottle. Let the pipette 

 drain a few seconds, and remove it, but do not blow 

 out the last drops. It is essential that the milk be 

 measured with great accuracy, but there is less need for 

 exactitude with the acid or amyl alcohol, as slight 

 variations of these do not affect the results ; it is as well, 

 however, to cultivate a habit of accuracy. 



