276 
Original Communications, 
and sometimes burnt in the evaporation, which it is well 
known, constitutes the chief part of the preparation. 
Mr. M. says that the fixed oils, liquid or solid, animal or 
vegetable, may be preserved as long as desired, with the sim- 
ple care of keeping them in completely filled, and well corked 
bottles. 
All the ointments undergo rapid alteration, giving rise to 
rancidity, which renders them unfit for use. They should not 
be prepared in large quantities at a time ; and when the con- 
sumption is small, should be confined to a few only, of the 
most needful, such as simple, basilicon, tar, and mercurial 
ointments. The ointments of zinc, lead, and white and red 
mercury — the latter of which soon decomposes — are often 
kept ready prepared, and very improperly so, as the acridity 
peculiar to rancid lard, produces irritation when applied to 
sores. With simple cerate, two-thirds of the ointments in 
common use, may be prepared extemporaneously, by rubbing 
up with it in certain proportions, the different substances pre- 
viously levigated. For this purpose, I find a glass muller 
and marble slab, more convenient and serviceable than a pes- 
tle and mortar. In this manner may also be prepared such 
vegetable ointments as stramonium, cicuta, and others, by 
mixing with cerate the finely powdered leaves, or what is 
sometimes recommended instead, and which may be used 
when the leaves cannot easily be obtained, good extracts 
of these plants. 
" The essential oils from being used every day, are often 
exposed to the air, which changes them entirely. The only 
efficient mode I have found of diminishing this alteration, has 
been to mix them with an equal weight of alcohol of 36°. 
This alcohol, suitable to almost all essential oils, permits me 
better to fraction their use, and forms at the surface of the 
oil, a bath that isolates it from the air retained in the vessel, 
and greatly tends to its preservation. Oil of aniseed mixed 
in this way, has continued to crystallize as if it was un- 
mixed, and implicating in its solidification, three-fourths of 
alcohol.'" 
