108 Memoir upon Animal Fat. 
asserting that it arises from the absorption of the oxygen ‘of 
the atmosphere, I was anxious to ascertain if this was cor- 
rect. hee ty . 
After having poured the ointment, while yet liquid, into 
squares of paper, I placed one part of it under a bell-glass 
filled with air over mercury: at the end of 24 hours. no ab- 
sorption had taken place; yet the surface was uncommonly 
white. 
I placed another part of it under the receiver of an air- 
pump, and I suddenly made a vacuum, which I kept up for 
some hours, giving from time to time a stroke of the piston, 
which produced at first some bubbles of air. The ointment 
extracted from the vacuum was perfectly yellow, and re- 
mained always so, without the least change. 
‘I think, therefore, that this white crust 1s owing to the 
disengagement of the gases, whether azotic or nitrous, which 
takes place from every part of the interior towards the sur- 
face ; and they augment the volume of the ointment. The 
latter cools by degrees, and does not allow the gases to escape 
entirely ; one part of the gas remains, and forms an infinity 
of small white bubbles at the exterior part. 
In support of what I have here advanced it may be added, 
that when the ointment is left to cool in the vessel in which 
it had been melted, and particularly when it is heated a little 
more, the quantity of caloric given is sufficient to drive off 
all the gas, and the ointment remains constantly yellow, 
without experiencing any further alterations. 
In order to examine this compound, and to appreciate the 
chemical changes which might have taken place, I boiled 
an ointment which had been two years prepared, for half 
an hour with water. It became very clotted; the water was 
interposed in such a manner that it was difficult to separate 
the whole quantity from it. The water had acquired a yel- 
lowish colour from it, and a slightly bitter taste; it was 
scarcely acid at all, and did not contain an atom of mer- 
cury. ; 
In order to establish a comparison, I made use of fresh 
ointment, made within 24 hours; I exhausted it by warm 
water, which had almost the same characters as the wash- 
ings 
