:242 QUANTITATIVE ANALYSIS. 



Place in each of a series of flasks or bottles (with stop- 

 pers) 50 cc. of pepsin-hydrochloric acid. In each of another 

 series place 50 cc. of the pepsin-hydrochloric acid which 

 contains the weighed quantity of the material whose influ- 

 ence is to be tested, or add to a number of portions of the 

 pepsin-hydrochloric acid the material to be tested and dis- 

 solve it by shaking without warming. Then place in each 

 flask 20 cc. of the albumin solution, shake thoroughly, and 

 digest it at 40, shaking repeatedly during the digestion. 

 To avoid accidental errors, each mixture must be prepared 

 in duplicate. 



To determine the amount of nitrogen in the albumin 

 solution, heat 20 cc. of the solution with 15 cc. of concen- 

 trated sulphuric acid, 10 g. of potassium sulphate, and 0.5 g. 

 of copper sulphate. This determination is also to be made 

 in duplicate. The heating must be done at first with great 

 care, otherwise the determination may be lost from foam- 

 ing. When the heating has continued about one and one- 

 half hours and the oxidation is not then completed, it is 

 advisable to let cool, add 10 to 15 cc. of sulphuric acid and 

 heat again. When the oxidation is completed, which may 

 be accomplished even without the addition of potassium 

 permanganate, let cool, dilute the solution, let cool again, 

 put it in a measuring-flask and fill up to 100 cc. Twenty- 

 five or fifty cubic centimeters of the well-mixed solution are 

 used for the determination of the ammonia or amount of 

 nitrogen. To collect the ammonia 20 to 40 cc. of fifth-normal 

 hydrochloric acid are sufficient. The amount of albumin 

 is obtained by multiplying the amount of nitrogen found by 

 6.25. 



After the digestion of the albumin has continued the desired 

 number of hours, neutralize the mixture with dilute caustic 

 soda solution (half- or fourth-normal), heat to boiling, add 

 acetic acid to faintly acid reaction and 5 cc. of concentrated 



