94 BULLETIN 846, U. S. DEPARTMENT OF AGRICULTURE. 



requires about 15 minutes. Cool to room temperature, and make up to 

 the mark with washed alumina cream. The sample is then shaken 

 vigorously for 1 minute, is allowed to stand about 5 minutes, and then 

 shaken for 1 minute. Filter through a dry folded filter, and deter- 

 mine the reducing sugar in 50 cc. of the nitrate by the Munson and 

 Walker method. Calculate as dextrose, and express the results as 

 per cent on the wet basis. 



The washed alumina cream is prepared by washing ordinary alum- 

 ina cream five times by decantation, using enough water so that at 

 least half of the total volume may be syphoned off each time. 



On account of the volume occupied by the precipitate the results 

 are a trifle high. This error amounts to about 1.4 per cent for white, 

 3.3 per cent for whole egg, and 7 per cent for yolk. It is not custom- 

 ary to correct for this. 



INDOL AND SKATOL. 



Dilute a 200 cc. portion of sample with 500 cc. of water, acidified 

 with 40 cc. of 5 per cent acetic acid for white or whole egg, and with 

 20 cc. for yolk, coagulate in boiling water or live steam, and filter. 

 Steam distill the filtrate as rapidly as possible. Extract the distillate 

 (approximately 300 cc.) with ether in a separately funnel. To the 

 ether extract add about 3 cc. of water, and evaporate before an elec- 

 tric fan until the smell of ether has almost but not entirely disap- 

 peared. A trace of ether does not affect the result. Add 10 cc. of 

 water, filter, and apply the vanillin test to the filtrate. 



Vanillin test. — To 5 cc. of the solution to be tested add 5 drops of a 5 

 per cent solution of vanillin in 95 per cent alcohol and concentrated 

 sulphuric acid. The acid should be added in the proportion of 2 cc. 

 for each 5 cc. of solution being tested. If indol is present, an orange 

 color, soluble in chloroform, amyl acetate, or amyl valerianate, will 

 be formed. If skatol is present, a deep red to violet color, readily 

 soluble in chloroform, amyl acetate, or amyl valerianate, will be 

 formed. 1 



As confirmatory tests, if needed, the following are suggested: 



P-DimetJiylaminobenzaldeliyde test. — To the solution to be tested 

 add 1 cc. of a solution consisting of 4 parts of para-dimethylamino- 

 benzaldehyde, 380 parts of absolute alcohol, and 80 parts of concen- 

 trated hydrochloric acid, in such a way as to form two liquid layers. 2 

 If indol is present a purplish red color will be formed. 



Dimethylaniline test. — To 5 cc. of the test solution add 5 drops of 

 dimethylaniline and 4 cc. of concentrated sulphuric acid. If skatol 

 is present, a deep red violet coloration is formed. 3 



PRESERVATIVES. 



Formaldehyde. — The test may be made exactly as in milk. 4 

 Boric acid. — Make the test as in milk. 5 



' J. Biol. Chem. (1916), 24: 528. * Leach, Food Inspection and Analysis, 3d ed., page 268. 



2 Zeit. physiol. chem. (1906), 42 : 25. 5 Leach, Food Inspection and Analysis, 3d ed., page 182. 

 s J. Biol. Chem. (1916), 24: 527. 



