137 
that rancidity is the alteration which oils and fats undergo when not protected 
from the influence of air and light. “Such oils,” he says, “acquire a sharp, dis- 
agreeable taste and odor, their proportion of free acids gradually increases, and 
they undergo various other chemical alterations.” 
Schmid ™ differentiates between “sour fats,” “rancid fats,’ and “sour and 
rancid fats.” “A fat is sour,” he says, “when its content of free fatty acids is 
abnormally high but the free glycerine is unchanged. A fat is rancid when the 
proportion of free fatty acids is not high but the free glycerine has been oxidized 
partially or completely to aldehydes and ketones. A fat is rancid and sour 
when it contains a large amount of free acid together with oxidation products 
of glycerine.” As a test for rancidity he proposes a 1 per cent solution of 
m. phenylendiamin, 
Seala * found cnanthylic aldehyde among other substances present in rancid 
olive oil, and assumes that this body gives the characteristic odor and taste 
termed “ rancidity.” 
Bianchi proposes, as a test for rancidity, to shake up a little of the oil in 
question with fuchsin-sulphurous acid, a violet-red color indicating rancidity. 
Brown ™ uses this same test in the study of butter fat, and presumes that the 
rancid odor is due to acrolein. Various other tests for rancidity have been 
proposed, all depending on the presence of aldehydes. 
The most satisfactory, in my experience, is that with fuchsin-sul- 
phurous acid, shaking up about equal parts of oil and reagent. Nearly 
all the samples of coconut oil prepared in this laboratory, after standing 
for several months, responded to this test, but they gave, not a violet red, 
as has been stated to be the case with other rancid oils, but a more or less 
blue coloration with only a slight tinge of red. The above review of the 
literature will demonstrate that the causes of rancidity are by no means 
clear. Certainly cenanthylic aldehyde has not an intensely disagreeable 
odor; acrolein has, but then it gives a red and not a blue color with 
fuchsin-sulphurous acid. 
ACTIVE OXYGEN IN COCONUT OIL WHICH HAS BEEN STANDING. 
Another peculiarity of pure coconut oil is that, after it has been stand- 
ing exposed to light and air for a few months, it almost in variably 
contains active oxygen. Five cubic centimeters of sample “ A,” shaken 
in an Khrlenmeyer flask with a mixture of 50 cubic centimeters of water, 
5 cubic centimeters glacial acetic acid, and 1 gram potassium iodide and 
allowed to stand for one hour, produced a deep-yellow coloration in the 
: oe o . ; N ‘ ; . 
water solution, requiring 0.25 cubic centimeter i0 sodium thiosulfate for 
decolorization, A blank test, with freshly prepared oil, remained per- 
fectly colorless during the same time. A simple way of performing this 
test is to saturate a strip of starch iodide paper with the oil in question, 
“A. Schmid: Zur Priifung der Fette auf Ranziditiit. Z. Anal, Ch. (1901), 37, 
301. 
'* Alberto Scala: Staz. sper. Agrar. ital, 30, 613, Centrbl. (1898), 439. 
* Centrbl. (1898), TI, 948. 
” Brown: The Chemistry of Butter Fat. Jour. Amer. Chem. Soe. (1899), 21, 
