BOTANIC MATERIA MEDICA, 349 
OLEA VOLATILIA—VOLATILE OILS. 
THESE volatile principles of the leaf, flower, 
seed and fruit, with the exception of orange and 
lemon oils, are obtained by distillation, and are 
also known by the names of distilled or essen- 
tial oils. They are distinguished from the 
fixed oils (which are obtained by expression) by 
being readily soluble in alcohol, ether and chlo- 
roform; by communicating their odorous prop- 
erties to water, and by leaving no stain upon 
bibulous paper. With the exception of mus- 
tard and bitter almond oils, they exist, already 
formed, in the substances from which they are 
obtained. The mustard and almond require to 
be macerated in water and subsequently dis- 
tilled to produce the volatile principle which is 
decomposed by certain principles stored within 
the seeds. The oils of orange and lemon are 
procured by scarification and wiping with 
sponges, etc. 
