22 MILK ANALYSIS 



flask. With the larger form of flask the dilution is made at once 

 by the cautious addition of 200 c.c. of water. Granulated zinc, 

 pumice stone, or 0.5 gram of zinc dust is added. 50 c.c. of the 

 strong sodium hydroxid solution, or sufficient to make the re- 

 action strongly alkaline, should be slowly poured down the side 

 of the flask so as not to mix at once with the acid solution. 

 It is convenient to add to the acid liquid a few drops of phenol- 

 phthalein or azolitmin solution, to indicate when the liquid is 

 alkaline, but it must be noted that strong alkaline solutions 

 destroy the former indicator. The flask is shaken so as to 

 mix the alkaline and acid liquids and at once attached to the 

 condensing apparatus. The receiving flask should have been 

 previously charged with a carefully measured volume of the 

 acid (100 c.c. is a convenient amount). The distillation is 



2 V 



conducted until about 150 c.c. have passed over. The acid is 

 then titrated with standard alkali and methyl orange, cochineal, 

 or azolitmin, and the amount neutralized by the distilled am- 

 monium hydroxid determined by subtraction. Each c.c. of - 

 acid neutralized is equivalent to 0.007 nitrogen. The nitrogen 

 multiplied by 6.38 gives the total proteids. 



The distillation in this operation requires care, as the amount 

 of ammonium hydroxid is determined by its neutralizing power, 

 hence solution of the alkali of the glass will introduce error. 

 Common glass is not satisfactory. Block-tin is a good material. 

 Moerrs found that Jena-glass tubes resist the action . of the 

 ammonium hydroxid. 



The most satisfactory condensing arrangement for general 

 laboratory use is a copper tank of good size, through which 

 several condensing tubes pass. Such an arrangement is shown 

 in side-view in figure 5. A detailed view of the construc- 

 tion as applied to Kjeldahl distillations is also shown in figure 

 5, which is a rough sketch, not drawn to scale. The flask is the 

 standard Jena-glass distilling flask, about 12 cm. diameter, the 

 tank should be high enough to allow of a condensing tube 60 



