IpO MODERN METHODS OF TESTING MILK 



filtrate, standardized sodium hydroxide solution is run 

 until neutral. The solutions are so standardized that 

 i cc. is equivalent to i per cent, of casein in the milk 

 examined. Therefore, the number of cubic centi- 

 meters of standard acid used, divided by 2, less the 

 amount of standard alkali used in the final titration 

 gives the percentage of casein in milk. The operation 

 usually requires 12 to 15 minutes when apparatus and 

 solutions are at hand in convenient form ready for use ; 

 several determinations can be carried on at the same 

 time to advantage. 



Apparatus. Most of the apparatus is such as is in 

 common use in dairy work in acidity testing (p. 131). 



(1) Two SQ-CC. burettes accurately graduated to 

 one-twentieth cubic centimeters. Automatic burette- 

 fillers save much time. 



(2) Flasks, volumetric, holding 200 cc. and accu- 

 rately marked. For greatest convenience, flasks hav- 

 ing necks 4^2 to 5 inches long and 4 inches inside 

 diameter are preferable. 



(3) Pipette (Babcock-test form), accurately gra- 

 duated to deliver 17.5 cc. (18 grams) of milk. 



(4) Pipette graduated to deliver 100 cc. 



(5) Pipette graduated to deliver about i cc, and 

 provided with a rubber bulb (so-called dropper). 



(6) Cups, plain white, holding 200 cc. or more. 



(7) Funnels, glass or granite-ironware, 3 to 4 inches 

 in diameter. 



(8) Filter-papers cut round, 6 to 7 inches in dia- 

 meter; or filters of fine linen cut to proper size and 

 shape, which can be used repeatedly, being thoroughly 

 washed each time. 



