EXAMINATION OF FROZEN EGG PRODUCTS. 93 



nearly to the 100 cc. mark with ammonia-free water. Add 2 cc. of 

 Nessler solution, fill the flask to the mark with ammonia-free water. 

 Close the flask with a thoroughly washed rubber stopper, and shake 

 well. Compare the color in a Duboscq colorimeter 1 with that of a 

 known standard made up at the same time, and containing 2 cc. of 

 approximately N/20 sulphuric acid. Express the results as milli- 

 grams of ammonia nitrogen per 100 grams of sample on the wet basis. 



It is essential that a blank experiment be run, using a known 

 amount of pure ammonium sulphate (containing about 0.3 mg. of 

 nitrogen) and 25 cc. of ammonia-free water, instead of the egg mate- 

 rial. Such an experiment should show over 95 per cent recovery. It 

 is also essential to run blank experiments with the reagents and water 

 used. 



This method while more rapid is not as accurate as the titration 

 method. If it is employed for samples where legal action may be 

 involved, it should be run in triplicate, and the average of the three 

 determinations used. 



PTiosfhotungstic acid method. — Weigh 5 grams of well-mixed sample 

 in a tared 100 cc. glass-stoppered Erlenmeyer flask. Add 45 cc. of 

 phosphotungstic acid solution made up as follows: Water, 420 cc. ; 

 1 per cent sulphuric acid, 10 cc. ; 20 per cent phosphotungstic acid, 

 20 cc. Shake well. Let stand 5 minutes, and filter through a folded 

 ammonia-free filter paper. Transfer to an aeration cylinder 10 cc. 

 of filtrate, which corresponds to 1 gram of sample; add 2 drops of 

 white petroleum oil, and 1 cc. of 10 per cent solution of sodium 

 carbonate. Aerate strongly for J hour into 3 cc. of 1 per cent sul- 

 phuric acid. The same chain of apparatus as that described for the 

 nesslerization method (p. 92) should be used. Nesslerize with 0.25 

 cc. of a Nessler solution made with mercuric iodid, dilute to 10 cc. with 

 ammonia-free water, and compare with a standard prepared with 0.03 

 mg. of nitrogen in the form of ammonium sulphate in 10 cc. volume. 



If a heavy red precipitate forms on adding Nessler solution, add 

 just enough 5 per cent acetic acid to dissolve it, dilute to about 45 cc, 

 again add Nessler solution, and make up to 50 cc. Make the neces- 

 sary change in the calculation for the greater dilution. Express the 

 results as milligrams of ammonia nitrogen per 100 grams of sample 

 on the wet basis. 



This method is good for rapid and approximately accurate work, 

 but should not be used for samples where legal action may be involved. 



REDUCING SUGAR. 



Wash 25 grams of sample into a 200 cc. graduated flask with 75 cc. 

 of water. Make slightly acid by adding 2 cc. of 5 per cent acetic acid 

 for white or whole egg and 1 cc. for yolk. Mix, and immerse the flask 

 in boiling water until the egg material is thoroughly coagulated. This 



i The Schreiner instrument gives results which are too low. 



