Pharmacy, 
Ihey have sent forth any flowers ; and others, 
as thyme, when the flowers have just ap- 
peared. All fragrant herbs yield a larger 
proportion of oil, when produced in dry 
soils and in warm summers, than in opposite 
circumstances. On the other hand, some 
of the disagreeable strong-scented ones, as 
wormwood, are said to contain most oil in 
rainy seasons, and when growing in moist 
rich grounds. 
Several chemists have been of opinion, 
that herbs and flowers, moderately dried, 
yield a greater quantity of essential oil’ 
than if they were distilled when fresh. It is, 
however, highly improbable, that the quan- 
tity of essential oil will be increased by 
drying ; on the contrary, part of it must be 
dissipated and lost. But drying may some- 
times be useful in other ways; either by 
diminishing the bulk of the subject to be 
distilled, or by causing it to part with its 
nil more easily. 
The choice of proper instruments is of 
great consequence for the performance of 
this process to ad vantage. There are some 
Oils which pass freely over the swan-neck 
of the head of the common still : others, 
less volatile, Cannot easily be made to rise 
So high. For obtaining these last, we 
would recommend a large low head, having 
a rim or hollow canal romid it: in this 
Canal, the oil is detained in its first ascent, 
and thence conveyed at once into the re- 
ceiver, the advantages of which are sutE- 
Ciently obvious. 
With regard to the proportion of water 
to be employed ; if whole plants, moderate- 
ly dried, are used, or the shavings of woods, 
as much of either may be put into the 
Vessel, as, lightly pressed, will occupy half 
its cavity ; and as much water may be added 
p will fill two thirds of it. When fresh and 
juicy herbs are to be distilled, thrice their 
weight of water will be fully sufficient; 
but dry ones requii e a much larger quan- 
tity. In general, there should be so much 
water, that after all intended to be distilled 
has come over, there may be liquor enough 
left to prevent the matter from burning to 
the still. The water and ingredients,” al- 
together, should never take up more than 
three fourths of the still; there should be 
liquor enohgh to prevent any danger of an 
empyreuma, but not so much as to be apt 
to boil over into the receiver. 
The subject of distillation should be ma- 
cerated in the water Until it be perfectly 
penetiated by it. To promote this effect, 
woods should be thinly shaved across the 
grain, or sawn, roots cut transversely into 
thin slices, barks reduced into coarse pow- 
der, and seeds slightly bruised. Very com- 
pact and tenacious substances require the 
maceration to be continued a week or two, 
or longer ; for those of a softer and looser 
texture, two or three days are sufficient ; 
while some tender herbs and flowers not 
only stand in no need of maceration, but 
are even injured by it. The fermentation 
Which was formerly prescribed in some in- 
stances, is always hurtful. 
With regard to the fire, the operator 
Ought to be expeditious in raising it at first, 
and to keep it up during the w'hme process, 
to such a degree only, that the oil may freely 
distil ; otherwise the oil will be exposed to 
an unnecessary heat; a circumstance which 
ought as much as possible to be avoided. 
Fire communicates to all these oils a dis- 
agreeable impregnation, as is evident from 
their being much less grateful when newly 
distilled, than after they have stood for 
some time in a cool place : and the longer 
the heat is continued, the greater alteration 
it produces in them. 
The greater number of oils require for 
their distillation the heat of water strongly 
boiling ; but there are many also which rise 
with a heat considerably less ; such as those 
of lemon and citron peel ; Of the flowers of 
lavender and rosemary, and of almost all 
the more odoriferous kinds of flowers. We 
have already observed, tliat these flowers 
have their fragrance much injured, or even 
destroyed, by beating or bruising them - 
it is impaired also by the immersion in 
water in the present process, and the more 
So in proportion to the continuance of the im- 
mersion and the heat ; hence oils, distilled in 
the common maimer, prove much less agree- 
able in smell than tlie subjects themselves. 
For the distillation of substances of this 
class, another method has been contrived; 
instead of being immersed in water, they 
are exposed only to its vapour. A proper 
quantity of water being put into the bot- 
tom of the still, the odoriferous herbs or 
flowers are laid lightly in a basket, of 
such a size that it may enter into the still, 
and rest against its sides just above the 
water. The head being then fitted on, 
and the Water made to boil, the steam, 
percolating through tlie subject, imbibes 
the ml, without impairing its fragrance, and 
carries it over into the receiver. Oils thus’ 
obtained, possess the Odour of the subject 
in an exquisite degree, and have nothing of 
the disagreeable scent perceivable in those 
