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BRITISH PHARMACEUTICAL CONFERENCE. 
almost invariably accompanied by obscure products of decomposition of an 
offensive and noxious character. 
Palm oil is, I believe, the only fat tliat has been observed to separate dis¬ 
tinctly into acid and glycerine. 
It will throw much light on the nature of the change if we carefully 
watch its progress from the first appearance until the full development of 
rancidity. 
That is done with most ease in ointments containing colouring matter of a 
vegetable origin, such as savine, or mineral, as oxide of mercury ; but in pure 
lard it is not difficult. 
The best chemical test of rancidity I find to be iodide of potassium, which 
when mixed with fat in the least degree affected, quietly assumes an orange 
colour, indicative of the presence of free iodine, the tint being directly pro¬ 
portional to the amount of rancidity. Thus I have found that when added 
to fat extremely rancid, the coloration is intense and immediate ; when 
added to mixtures of this fat and other perfectly neutral, the coloration is 
less and less according to its dilution, and is plainly perceptible when the fat 
contains only one-twentieth, but a longer time is required for its development. 
Acidity cannot be relied on as the index, for it will be found, that whereas 
the highly rancid fat, when boiled with alcohol, yields a solution reddening 
decidedly, though not promptly, litmus-paper, a mixed fat, such as the above, 
gives a negative result. 
When rancidity first shows itself in a pot of lard that has been filled with 
the melted fat and not subsequently disturbed, the following phenomena may 
be observed. Here and there throughout its contents, but more especially at 
the points where the lard touches the sides of the stoneware jar, small patches 
of a whiter and more crystalline aspect than the bulk have made their appear¬ 
ance. If these patches are tried by iodide of potassium, they will be found to 
be highly rancid, whilst the surrounding parts retain unimpaired their original 
freshness. As the process advances, these patches increase in size and number, 
until the whole mass has become infected. How far the action would proceed 
if time were given it is uncertain, but ordinary cases of rancidity are caused 
by the splitting up of a small portion only of the fat. From the change 
taking place in situations to which the air cannot be supposed to penetrate,— 
for instance, the interior of a homogeneous mass of fat,—it may be inferred 
that air is not necessary to its propagation. Analogy coupled with the ob¬ 
servation that rancidity first makes its appearance at the sides of the vessel, 
where possibly from contraction during cooling a small air-space may have been 
left, point to the necessity of air being present at its commencement. In fact, 
it is pretty sure that the phenomena are caused by a species of fermentation 
involving the joint action of air, water, albuminous matter, and a moderate 
degree of heat. Such is the opinion of M. Pelouze, who has written much 
on the question, and of whose valuable labours I have freely availed myself. 
There can be no question of the presence of water in all natural fats ; albu¬ 
minous matter in some form may also be safely assumed to be in company 
with it. It is often met with in a flocculent form at the bottom of jars of 
olive oil, and cannot fail to be present in all fats of animal origin, whilst 
MM. Saussure and Pelouze have noted the absorption of oxygen during the 
drying of siccative oils, some of which in return evolve hydrogen and car¬ 
bonic acid. I have myself observed a candle lowered into a jar partly filled 
with cod-liver oil, that had remained some time in contact with the air in the 
upper part of the vessel, suddenly extinguished. It is doubtless true, on the 
supposition of a ferment being the agent that effects the disturbance, that 
the removal of any one of the essential conditions would prevent its action. 
But can it be done in a practical way ? I believe not. To remove the last trace 
