178 



a clear and fasl filtering separation, but if tin- milk is low in casein a lit t i - 

 • acid should t>< used. precipitate ia now filtered thr 



a filter (9-11 cm. filter), the flask rinsed out thoroughly and poured on the 



filter, preferably cold. U a - a tream of water is directs -• the 



filter, the casein washing is facilitated. About 23 cc. of water should 



- 'hrough the filter to insure the removal of all tr; • 'i<- add. The 



preeipita T ' s er with the filter paper, is now returned to the Erlenmi 

 flask in which the preeipitation was made. To this is now added 7~ 

 distilled water, in- and then a few drops of phenol- 



pthalein and 10 cc. of *, potassium hydroxide. A rubber stopper i> placed 

 in the flask and the contents shaken vigorously. Complete solution is easily 

 indicated by the disappearance of the ■white rascin particles. After solution 

 the stopper is rinsed off into the flask with carbon dioxide : and 



immediately titrated with j* s acid to the disappearance of the red eolor. 

 It is necessary that a blank be run parallel with the determination. Fur 

 example, suppose it required 7.20 ec. of arid to make the pink color just 

 disappear and the blank amounted to .2 cc, the percent of casein would be 

 10 — 7.4 = 2.60 per cent, casein. Precai First, water 



from carbon dioxide, must be used. Second, the titration should be made 

 >n as solution of casein has taken place. This will be from half an hour 

 to an hour after adding the ^ alkali. Repeated shaking hastens solution. 



Results obtained by Hart as compared with the official method. 



PERCENT CASEIN. 



Volumetric Method 

 Official Method. (Hart 



.. 78 



3.12 3.05 



2 -7 2.8S 



1.90 1.8.5 



_ " 



The next volumetric method to be considered is the Formol titration 

 method. This is perhaps the most rapid method of the three volumetric 

 methods, for estimating the proteids in milk. It was pointed out in 1900 

 by Hugo Schiff that when formaldehyde was added to amino acids, the acid 



