F.S. Hammett 383 
analysis. This lends additional support to the contention of 
Van Slyke and Cullen (8) that longer periods of aeration as ad- 
vanced by Fiske (8) and others are unnecessary. Table II gives 
a few of the results demonstrating this point. 
Repeated tests have been unable to demonstrate the carrying 
over into the receiving flask of any alkaline spray from the 
aerated mixture mentioned by Sumner (1) as a reason for dimin- 
ished vigor in aeration. A comparison of the traps used by Sum- 
ner and those of this laboratory shows a markedly higher effi- 
TABLE II. 
NH; Recovered from Varying Amounts of Placenta Tissue When Uniformly 
Aerated for 30 Minutes. 
100 Gm. of tissue. 
Specimen No. | Weight of tissue. 
0.01 n NHs 0.01N HC] NH; 
gm. ce. COs mg. 
10 9.95 8.60 10 Zee 
ee 8.97 10 2.4 
46 6.65 8.40 10 Ae] 
5.12 8.76 10 4.] 
29 7.29 6.00 10 9.3 
5.97 6.71 10 9.4 
46 a iako 5.80, 20 33.8 
4.45 Ler 20 33.9 
ciency in this respect for the latter. Foaming is easily prevented 
in the aerated mixture by the addition of 1 cc. of a solution con- 
taining equal parts of amyl alcohol, toluene, and ethyl alcohol. 
The use of long-necked 100 cc. flasks prevents loss by spattering, 
and the foaming in these containers is reduced to a minimum by 
the addition of a few drops of the above mixture from time to time. 
Factors Influencing the Ammonia Fraction in the Urea 
Determination. 
The quantity of urea in any given sample is usually determined . 
by the difference between the ammonia already present and the 
total ammonia blown over after the action of urease. Having 
