78 
Journal of Agricultural Research 
Vol. XXVI, No. a 
The low iodin number places this oil in the nondrying class. The 
acid value is high for a fresh oil extracted from sound material, and this 
is probably due to a very active fat-splitting enzym in the tuber. The 
percentages of saturated and unsaturated acids were determined by the 
lead-salt-ether method and corrections made for the small amount of 
the unsaturated acid fraction which is weighed with the saturated acid 
fraction (j, j). The sum of the percentages of saturated and unsat¬ 
urated acids is 92.9, instead of approximately 95.0, which would have 
been expected if the oil had been refined. The low summation is due to 
the presence in the oil of nonfatty material as mentioned above. The 
low Reichert-Meissl and Polenske numbers indicate the presence of only 
a trace of volatile fatty acids. 
UN SATURATED ACIDS 
The iodin number of the unsaturated acid fraction (96.9) indicates 
that it consists almost completely of oleic acid. The bromin addition 
derivatives of the unsaturated acids were prepared (6, p. 579). No 
hexa-bromid, the derivative of linolenic acid, was found, but a small 
amount of linolic tetrabromid, m. p. 114.0, was obtained. Using the 
iodin number of the unsaturated acid fraction and the theoretical 
iodin numbers of oleic acid (90.1) and linolic acid (181.4), the percentage 
composition of the unsaturated acid fraction was calculated to be 7.4 
per cent linolic acid and 92.6 per cent oleic acid, or 5.9 per cent linolic 
acid glycerid and 73.3 per cent oleic acid glycerid in the original oil. 
SATURATED ACIDS. 
A quantity of saturated acids prepared by the lead-salt-ether method 
was esterified with methyl alcohol (5). This mixture of methyl esters 
was then fractionally distilled under diminished pressure. The data for 
this distillation are given in Table I. The mixture was divided into 
five fractions, designated by the letters A to E, and a residue by a pre¬ 
liminary distillation from a 1-liter Claisen flask. These preliminary 
fractions were redistilled from a 250-cc. Ladenburg flask, as indicated 
in the table, and eight fractions and a residue obtained. 
The iodin numbers, which are a measure of the contaminating unsat¬ 
urated acids, and the saponification values of these fractions, are given 
in columns 2 and 3 of Table II. From the iodin numbers of these 
fractions the percentage of unsaturated acids in each fraction was 
calculated, and from these data the mean molecular weights of the 
saturated acids in each fraction were calculated as given in column 6 (2). 
