THE ANALYSIS OP MILK 35 



tared filter-paper ; remove the precipitate completely 

 from the beaker by means of a policeman, and wash well 

 (Fig. 22). Dry in the water-oven, and extract the fat 

 with ether, preferably in a Soxhlet extractor, and dry 

 again till the weight is constant. Ignite the precipitate 

 in the Gooch crucible, or place the filter containing the 

 precipitate in a weighed basin and ignite it (if tared 

 filters are used the tare should also be ignited in a 

 weighed basin) ; subtract the weight of the ash 

 (corrected if necessary for the ash of the tare) from the 

 weight of the precipitate, and the difference will give 

 the weight of the proteins. 



Estimation of Casein and Albumin. Pipette 

 10 c.c. of milk into a beaker, add 90 c.c. of water at 

 43-43 0. and 1.5 c.c. of a 10 per cent, solution of 

 acetic acid ; stir well, and collect and weigh the 

 precipitate as above. [Note. This estimation or that 

 given above may be combined with a fat estimation.] 

 The precipitate is in this case casein. 



Raise the filtrate to boiling, and keep for 15 minutes 

 on the water-bath ; collect the precipitate as above, 

 and weigh after drying ; as fat and ash are absent the 

 extraction and ignition may be omitted. The precipi- 

 tate consists of albumin. 



Estimation of Nitrogen by KjeldahPs Method. 

 5 c.c., or 10 c.c., of milk are pipetted into a long- 

 necked hard glass flask ; 20 c.c. pure sulphuric acid 

 and a drop of mercury are added ; a long-stemmed 

 bulb is placed in the neck ; the flask is supported 

 in an inclined position, and it is heated by a small 

 flame ; at first water is driven off, next a consider- 

 able amount of frothing takes place, and when this 

 has subsided the flame may be turned up to such a 

 height that the sulphuric acid distils up to and is con- 

 densed in the neck; 10 grammes of acid potassium 

 sulphate may be added after the frothing has subsided, 

 but this addition is hardly worth while with milk, as 

 the operation is fast enough without it ; the heating is 

 continued till the liquid in the flask is quite colourless. 



