126 xM E M O I R S ^Z' the 
extra6led from trunks, or other parts of vegetables, do certainty 
take fire, and flame ; wherefore obferving, that thofe that do not 
take fire or flame, do yet make as great an explofion and ebulli- 
tion, and probably as great a heat, as thole that did, one might 
be apt to impute this to the lightnefs and too great fubtility and, 
volatility of thoie eflential oils, whofe very attive particles too 
loon exhale, or fly away j and this conjecture feems to be juftified 
by the addition of a more rampus body, as balfam of fulphur 
made with oil of turpentine, to the mod volatile and fubtile oils, 
which then produce a flame, whofe particles being grofl^er, or 
more ramous, will detain the more volatile oil from too fudden 
an explofion, and give more time to the fiery fpirit -to penetrate, 
and mix itfelf with thole combuftible materials 5 and this may be 
one reafon, why the ponderous oils diftilled from the roots or 
ligneous parts of a plant do all take fire ; viz. becaule the parts 
of this fort of oil, lying cloler together, do not fo foon diffipate 
after the fpirit is thrown upon it • and then, as to the fpecific 
oravity, the difference is alio very confiderable, which any one 
may find by this familiar way 3 if you fill a glafs with one ounce 
of the effential oil of the leeds, you will require nine drachms of 
the ponderous oil of the vegetable to fill up the fame fpace • this 
is alfo obvious to any fpe6lator, that moft of thefe oils, thus 
diftilled, are more ponderous than common water, by their fink- 
ing to the bottom ^ whereas all eflential oils, extra6led from the 
leedy parts, do fwim on water, and Ibme are lighter than the 
beft re6lified fpirit of wine, but moft of them are lighter than 
brandy, which has made the Chemifts call them etherial oils. 
In the catalogue of experiments, you may find which are the 
ponderous oils that do conftantly take fire: Moreover, the 
ponderous oils have yet one advantage over the lighter vola- 
tile oilsj for being expoled to a longer and greater degree of 
fire than the othe'rs, they unite more igneous particles, which 
being put into motion, may contribute Ibmething to caule this 
accenfion. 
The oils diftilled from animal bodies do all of them take fire 
and flame, but with this difference, that they do not produce lb 
great an explofion as the vegetable do, but do more certainly 
take fire, and continue their flame longer, but not fo fierce as the 
other. If we rightly examine the conllitution or texture of this 
oil, we have ieveral properties adapred to the production of this 
effect ; there is a much greater degree of fire required in the 
diftillation of this oil than is necefliry for that of the vegetable 5 
a greater quantity alio of volatile lalts do pafs over vvirh the oil ; 
and 
