664 LABORATORY HINTS 



(3) To Estimate Fat. 



Weigh lo c.c. of milk. 



Place it into a Stoker's graduated tube. 



Add lo c.c. concentrated HCI and heat cautiously till brown. 



Cool and fill up to the 50 c.c. mark with ether. 



Shake Avell and allow ether to settle out. 



Read off the volume of ether, say 26 c.c. 



Pipette out 10 c.c. of ether solution into a small weighed glass flask. 



Evaporate ether, dry flask in oven for one hour. 



Cool and weigh. 



If a Stokes tube is not available heat the milk in a large test-tube, 

 and transfer when cool to a graduated 100 c.c. cylinder. Wash out 

 the tube with ether and place same in the cylinder, and the volume is 

 now made up to 50 c.c, and the process continued as described above. 



Example : — 



Flask fat 2y^yi 

 Flask 23-421 



o'i5o 

 In 10 c.c. of ether there is o"i5 of fat 

 In 26 c.c. of ether there is o"i5 x 26 



= 0-39 



10 

 The amount of fat in io"2i3 grm. of milk (10 c.c.) = 0*39 

 The amount of fat in loo grm. of milk 0*39 x o"ioo 



= 3"8i per cent. 



IO"23I 



(4) To Estimate Solids not Fat. 



Subtract the fat from the total solids. 



Example : i3'32 — 3"8i = 9"5i per cent, of solids, not fat. 



(6) To Estimate Lactose (Fehling's method). 



Pipette 20 c.c. milk into a 100 c.c. graduated flask. 

 Add a few drops of acetic acid. 



Mix well, place on a water bath for a few minutes. 

 Cool and make up to 100 c.c. with distilled water, shake and filter, 

 Fill a burette with this solution. 



In a porcelain basin place 10 c.c. of Fehling's solution. 

 Add 40 c.c. of water and boil. 

 Run in milk solution from the burette slowly. 



Continually try a few drops of liquid from the dish with a starch 

 and KI paper. 



When it ceases to give a blue colour stop burette flow. 



Keep the liquid gently boiling during the process. 



For the indicator it is handy to have a series of test-tubes. 



In each place 2 c.c. of the indicator and one drop of acetic acid. 



