374 Foam Inhibitor 
as the result of interactions with the reagents in the decomposition 
chamber of the apparatus. 
We have been able to confirm the conclusion of Van Slyke that 
amyl alcohol also increases the gas volumes in amjno nitrogen de- 
terminations, though its effect on the blank is negligible. The 
excess gas due to the amyl alcohol seems to be roughly propor- 
tional to the amount of amino nitrogen in the sample. | 
Lee’s work? on foam inhibitors for the urease method of deter- 
mining urea, in which the solutions are subjected to rapid aera- 
tion for the removal of the ammonia formed, lead him to recom- 
mend a mixture of 70 per cent phenyl ether and 30 per cent amyl 
alcohol. He claims that this mixture is more effective than either 
‘substance alone or than caprylic alcohol. We have tried this 
mixture of Lee’s in the Van Slyke method, only to find that an 
effect was produced on the gas volumes obtained in the course of 
actual determinations, though no effect on the blank could be 
detected. Phenyl ether alone, however, proved to be without 
effect, as the following experiments indicate. 
10 cc. of an asparagine solution produced in two determinations 16.70 
and 16.80 ec. of gas. With 0.2 cc. of phenyl ether and 10 cc. of this solu- 
tion, two other determinations under the same conditions of temperature 
and pressure gave 16.69 and 16.72 cc. of gas. Two other determinations in 
which the phenyl ether was replaced by Lee’s foam-inhibiting mixture gave 
17.18 and 17.19 ce. of gas. Evidently this effect is produced by the amyl 
alcohol. . 
In another experiment a solution of Kahlbaum’s leucine was used. 10 
ec. portions of this solution gave 9.70 and 9.73 ce. of gas in two determina- 
tions in which no foam inhibitor was used. With0.2 cc. of phenyl ether, 
two more determinations under the same conditions gave 9.75 and 9.73 
cc. of gas. 
Phenyl ether thus appears to have no effect on the volume of 
gas produced in a Van Slyke determination, even when present 
in excess. Furthermore, according to our experience it is a very 
effective foam inhibitor, more effective than either amyl or second- 
ary caprylic alcohol. Certain solutions that have foamed ex- 
cessively with amyl alcohol added in amounts as large as 0.5 cc., 
during a Van Slyke determination, can now be analyzed with the 
addition of only two drops of phenyl ether, with very little if 
any foaming, even when the apparatus is shaken over 300 times 
per minute. ; 
