ON THE RANCIDITY OF FATS. 
253 
The remainder was gradually heated to 220° and kept at that temperature 
for five minutes=No. 3. It was much firmer than either of the preceding, 
and maintained that distinction after being stirred. 
Of each of these lards I set aside, in willow boxes, three specimens, viz. 
lard well stirred, lard mixed with oil of pimento in the proportion of two drops 
to the ounce, lard mixed with oxide of mercury one drachm to the ounce,— 
and placed them where the temperature ranged between 70° and 80°. 
On the 21st of April (ninety days) I first observed a change in the lards 
mixed with oxide of mercury,—No. 1, strained at 140°, being the least, and 
No. 3, strained at 220°, the most altered. The scented and plain lards, tested 
with iodide of potassium, all produced slight coloration after half an hour, but 
the scented lards less than the plain. No. 3 appeared to better advantage than 
the less heated specimens. After thirty hours’ exposal on the slab to light and 
air, a most extraordinary change was observed. Nos. 1 and 2 of the plain 
lards had assumed an orange colour, No. 3 a similar tint, but only half as dark, 
whilst the scented lards had lost rather than acquired colour,—in fact pro¬ 
duced an ointment at that time perfectly saleable. The contrast was most 
striking, and continued so for two months ; by which time all the specimens 
were of an orange colour, but the scented lards only externally ,—probably 
affected by the fumes of the laboratory. 
These same lards were again examined July 7. Those mixed with oxide of 
mercury -were all hopelessly bad. The rest were tested with iodide of potas¬ 
sium and after eight hours’ exposure presented the following appearances :— 
Nos. 1, 2, and 3 of the plain were of a lemon colour, the tint of No. 1 being 
less than that of No. 2, of No. 2 less than No. 3. The scented lards still main¬ 
tained their superiority, Nos. 1 and 3 being quite useable, No. 2 not so. 
August 26, I again examined them, with the same results. 
I therefore conclude that oil of pimento, which of those that had main¬ 
tained the neutrality of oxide of mercury ointment appears the best adapted 
for the purpose, is a useful, agreeable, and easily applied remedy for prevent¬ 
ing or very much retarding rancification in fats and fatty mixtures. 
I think I am also justified in adding this corollary—that it is advisable 
when preparing ointments with a view to their preservation, to use ingredients 
retaining unaltered the odorous principles with which nature has for obvious 
purposes endowed them ; that is to say, I would use yellow wax instead of 
white wax, yellow olive oil instead of bleached olive oil. In fact, experiment 
has shown the superiority of these bodies not meretriciously tampered with, 
over the some bodies to which a false appearance of excellence had been given 
by exposure to bleaching agents, no matter how simple and apparently harm¬ 
less their nature. 
The experiments on the effect of temperature I have repeated more than 
once. They go to prove that it is not advisable to push the heat bcj’ond that 
of the water-bath, nor maintain it too long at that temperature. I say this 
feelingly, as the undecisiveness of my first experiment and a certain amount 
of belief in the old-wives’ tale about boiling lard, induced me to try the super¬ 
heating process on a large scale,—and most unfortunate was the result. 
I consider the British Pharmacopoeia process, where the flare is melted by 
water-bath, the fat strained from the membrane as soon as possible, and then 
dried by water-bath, to be an excellent one. I would only suggest the ad¬ 
visability of adding to it oil of pimento or balsam of Peru, in the proportion 
of 2 drops to the ounce, before placing it in stock. Such addition does not in 
any way interfere with its medicinal use, and would, as I have shown, much 
conduce to its preservation. 
Weymouth. 
