A FOAM INHIBITOR IN THE VAN SLYKE AMINO 
NITROGEN METHOD. 
By H. H. MITCHELL anv H. C. ECKSTEIN. 
(From the Department of Animal Husbandry, University of Illinois, Urbana.) 
(Received for publication, January 11, 1918.) 
This laboratory has experienced considerable difficulty recently 
in finding a suitable substance to prevent foaming during the 
determination of aliphatic amino nitrogen in animal and plant 
extracts according to the Van Slyke nitrous acid method. Kahl- 
baum’s secondary caprylic alcohol, recommended by Van Slyke, 
cannot be obtained on the market now, while other preparations 
we have tried have invariably affected the volume of gas not ab- 
sorbable by the alkaline permanganate solution. Thus, 0.2 cc.! 
of the secondary caprylic alcohol obtained from castor oil by re- 
fluxing with NaOH and subsequently distilling and fractionating,’ 
gave 1.00 cc. more of gas not absorbable by alkaline permanga- 
nate in an amino nitrogen determination, than was obtained in 
a duplicate determination in which no alcohol was used. A pre- 
paration of caprylic alcohol obtained from Eimer and Amend 
gave similar results, even when fractionally distilled. We at- 
tempted to overcome this effect by shaking the alcohol with gla- 
cial acetic acid and a 30 per cent solution of NaNO, previous to 
using, and were able in this way to reduce the effect to 0.3 ce. 
of residual gas. If the alcohol, treated in this manner, was run 
in with the reagents and shaken with them during the removal 
of the air from the apparatus, instead of being run in with the 
sample as is customary, the effect could be reduced still further. 
Unfortunately, however, this preliminary treatment of the alco- 
hol seemed to deprive it largely if not entirely of its foam-inhibit- 
ing character and therefore cannot be recommended. These ex- 
periments are interesting in showing that the vitiating effect of 
these caprylic alcohol preparations on the determination occurs 
1 This amount of foam inhibitor is of course excessive in routine work. 
2 Lee, O. I., St. Luke’s Hosp. Med. and Surg. Rep., 1917, iv; abstracted 
in Chem. Abst., 1917, xi, 2808, 3027. 
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THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. XXXIII, NO. 3, 1918 
