139 
In examining this table it will be noticed that in almost every case a 
distinct blue color with Schiff’s reagent is accompanied by a positive test 
for peroxide, and, in the two cases where a red coloration predominates, 
the peroxide test is negative. The strongest tests for both peroxide and 
aldehyde were given by samples A and B—two very pure oils—while, 
contrary to our expectations, the commercial oils as a rule either failed to 
respond entirely or gave very weak tests, though they were infinitely 
worse than the pure samples in every other particular. The only change 
noticeable in samples A and B, on standing, was the development of a 
peculiar, pungent, “strong” odor and a slight burning “after taste ;” other- 
wise they were practically the same as when freshly prepared. Just what 
this “strong” odor in pure oils is caused by can not at present be stated, 
although the subject is now being investigated. It can hardly be caused 
by either cenanthol or acrolein, as both these substances, when mixed 
with oil, give a red and not a blue color with Schiff’s reagent. Glycerine 
aldehyde** under certain conditions produces a blue-red coloration with 
this test, but it has no odor. However, the process by which this change 
is produced is undoubtedly due to direct oxidation by light and air, since 
bacterial or mold action may be excluded in the case of a pure oil. That it 
is largely a surface action is indicated by the facts that (1) samples A 
and B, which were kept in large bottles, about half full, have deteriorated 
in five months to a much greater extent than have other samples of pure 
oil which were kept in small, nearly full bottles for over a year; (2) both 
the aldehyde and peroxide tests were given by samples of fresh oil which 
were exposed to the air on strips of filter paper for one or two weeks ;22 
(3) the same effect can be produced by treating fresh oil with platinum 
black for a few hours, or by heating it, exposed in a thin layer, to 100° 
for ten or twelve hours. 
A possible explanation of this production of rancidity in pure oils is 
that a small percentage of fatty acid is oxidized to an oxyacid, which in 
turn forms a lactone, and (assuming the formation of hydrogen peroxide) 
the latter would give rise to a peracid, which, in turn, would oxidize the 
free glycerine to an aldehyde. The absence of peroxide and, as a rule, of 
aldehyde in commercial coconut oils, or in those purposely subjected to 
the action of micro-organisms, may be due to the presence of sugars and 
other reducing substances commonly present in the impure oils, or to the 
fact that the glycerine set free by mold action is completely oxidized to 
carbon dioxide and water. ‘The nonexistence of free glycerine in highly 
rancid fats has been noted by Sparth** and other observers. ‘This ques- 
tion of the products arising from the oxidation of pure coconut oil by air 
is now being taken up more thoroughly, and the results will be published 
in a later paper. However, from a commercial point of view, it is of 
°K. Fischer u. Tafel. Ber. d. Chem. Gesell. (1887), 20, 3384. 
“Freer & Novy: Amer. Chem. J. (1902), 27, 161. 
3 Zt. Anal. Ch. (1896), 35, 471. 
