I A T R O P H A. ?oq 
Catalogue of the Royal Garden at Kew, it had been in¬ 
troduced before by Mr. Bentick in 1690. It flowers from 
May to July. 
Mr. Miller has another fort, found by Dr. Hbuftoun at 
Vera Cruz, where it was planted for ornament. Hav¬ 
ing leaves divided like the common wolfsbane, he names 
It Iatropha aconitifolia. It riles with a ftrong, brittle,' 
woody Italk, ten or twelve feet high, covered with a grey 
bark, and dividing into many branches. The leaves are 
armed with fmall flinging ('pines like tfiofe of the nettle. 
At the ends of the branches come out the flower-ltalks, 
which are five or fix inches long, and fuftain an umbel of 
white flowers. The males are one-petalled, and harve a 
pretty long tube, divided at top into five fegments ; the 
females expand in form of a role, and are fucceededby a 
globular, prickly, tricoccous fruit. It is probably a va¬ 
riety of the urens. 
13. Iatropha herbacea, or herbaceous phyfic-nut: prick¬ 
ly, leaves three-lobed ; Item herbaceous. This is an an¬ 
nual plant, riling with an herbaceous ftalk about a foot 
high, dividing into two or three branches; the whole 
clofely armed with long, briftly, flinging, fpines. The 
flowers grow in an umbel at the ends of the branches ; 
they are fmall, of a dirty white colour; three-lobed cap- 
iules, covered with the fame fpines as the plant. Native 
of Vera Cruz. 
14. Iatropha elaftica, elaflic-gum-tree, or caoutchouc : 
leaves ternate, elliptic, quite entire ; hoary underneath, 
on long petioles. The tree yielding that refin which is 
now commonly known under the ng/ne of elaftic gum, 
caoutchouc, or Indian rubber, is fuppofed to be of this 
genus ; but there are feveral others which yield a fimilar 
juice, as Ficus Indica, Cecropia peltata, Siphonia caout¬ 
chouc, Artocarpus integrifolia, and Urceola elaftica; and 
perhaps other ipecies of thofe genera, efpecially of the 
Iatropha and Siphonia. This tree is a native of Guiana, 
of Quito, and Braiil, particularly in Para, where it is call¬ 
ed majfaradub. The Indians by an incifion in the bark 
extract a vifcid white fubftance, like that which iffues 
from the fig-tree ; they receive it into earthen moulds, to 
make rings, bracelets, girdles, fyringes, hats, boots, flam¬ 
beaux, figures of animals, Sec. Abbe Rochon fays that 
the inhabitants of Madagafcar aifo make flambeaux of it, 
which burn without wicks, and afford them a very good 
light when they go out to filh in the night-time ; but he 
deferibes the tree which yields the elaftic gum in Mada¬ 
gafcar as twenty feet high, the leaves eight inches long 
and two inches broad, the fruit refembling a round fig, 
and full of fmall feeds. We may conclude therefore that 
this tree is the Ficus Indica ; certainly not an Iatropha. 
The coagulated juice however is of the fame nature. 
The firft account which we have of the elaftic gum or 
refin, or caoutchouc as it is called by the Indians to the 
fouth-eaft of Quito, is in a memoir by Monf. de la Conda- 
mine in the Memoirs of the French Academy for 1751, 
and in his relation of the river of Amazons in 1745. 
The tree which yields this fubftance grows along the 
banks of this river, and is very common in the forefts of 
the province of Emeralds to the north of Quito, where it 
is called hheve, and whence Aublet has taken his generic 
name, Hevea. The tree is deferibed as very lofty and 
ftraight, and quite naked up to the head, which is very 
fmall ; the trunk of the largeft is only about two feet in 
diameter. The foliage is not unlike that of the calTava, 
No. 10. The fruit is triangular, inclofing three feeds. Thefe 
feeds or kernels, peeled and boiled in water, yield a thick 
oil, which the Indians ufe as butter with their food. The 
wood of the tree is light and fit for mails. For the ge¬ 
neral hiftory of Caoutchouc, fee that article, vol. iii. 
p. 744; and for its chemical properties, as far as were 
then known, fee Chemistry, vol. iv. p. 340. to which the 
followdng remarks may now be added. 
Caoutchouc, when pure, is of a white colour, and with¬ 
out tafte or fmell; the black colour of the caoutchouc of 
commerce is owing to the method of drying it after it has 
Vol. X. No. 705. 
been fpread upon moulds. The ufual way is to fpread a 
thin coat of the milky juice upon the mould, and then to 
dry it by expoling it to frnoke; afterwards another coat 
is laid on, which is dried in the fame way. Thus the 
caoutchouc of commerce confifts of numerous layers cf 
pure caoutchouc alternating with as many layers of foot. 
Caoutchouc is not altered by expofure to the air. It 
is perfeftly infoluble in alcohol; but alcohol renders it 
colourlefs. It is perfectly foluble in ether. This pro¬ 
perty was firft pointed out by Macquer: Berniard, on the 
contrary, found it to be fcarcely at all foluble in fulphuric 
-ether, which was the ether ufed by Macquer; and that 
even nitric ether was but an imperfeft folvent. See vol. iv. 
p. 340. The difference in the refults of thefe two che- 
mifts was very lingular; both were remarkable for their 
accuracy, and both were too well acquainted with their 
fubjefl to be eafiiy milled. The matter was cleared up 
by Mr. Cavallo: he found that ether, when newly pre¬ 
pared, feldom or never dilfolved caoutchouc completely; 
but, if waflied previoully in water, it never failed to dif- 
folve the caoutchouc with facility. When the ether is 
evaporated, the caoutchouc held in folution is obtained 
unaltered; in this ftate, therefore, it might be employed 
to make inftruments of different kinds ; but that method 
would be too expenfive for ordinary purpofes. However, 
it has fince been difeovered that it may be melted by means 
of water only; fee vol. iii. p. 745, new edit. 
Another curious particular relative to caoutchouc is its 
electric property. This was difeovered and communi¬ 
cated as long ago as Nov. 1797, in the Monthly Magazine. 
The eleftric property may be alcertained in the following 
manner : Take a quarter of a Iheet of writing-paper, hold 
it to the fire till it be pretty warm, and then immediately" 
lay it upon a table, or any even furface; hold it there 
fteadily to prevent its flipping, and brifkly rub it, ten or 
a dozen times, in the fame direftion, with a piece of In¬ 
dia rubber. Now, upon attempting to lift the paper, it 
will be found to adhere clofely to the table; and, being 
fuddenly raifed, and again brought within a fmall dil- 
tance, it will be ftrongly attracted to the table. This is 
occafioned by a quantity of eleftric fluid accumulated 
between the table and the paper, by the friftion of the 
rubber; for, on prefenting a conducting body, the pa¬ 
per will be attracted to it. .Sparks, attended with a crack¬ 
ling noife, may be drawn from the paper in the ufual man¬ 
ner; which, when viewed in the dark, appear more lumi¬ 
nous than might at firft be fuppofed. It muft be fup¬ 
pofed, however, that unlefs the paper be lifted very expe- 
ditioufly from the table, the greater part of the fluid will 
efcape in doing it; and confequently, the paper will ex¬ 
hibit but fmall figns of electricity. Indeed, the quantity 
of fluid accumulated is always much greater than that 
which remains on the paper ; but in dry frofty weather,, 
the beft time for making the experiment, the quantity 
remaining will be confiderable. The paper muft be pre- 
vioufly warmed at the fire ; for continuing the friftion,. 
even till the paper grow's warm, has never lucceeded. 
Some new lights have alfo been thrown upon the na¬ 
ture and properties of this fubftance by the experiments 
of Mr. John Gough, as detailed in the Memoirs of the 
Manchelter Society, vol. i. fecond feries, 1806. Mr. G>. 
oblerved, that, when the fubftance was much diftended, 
a portion of its caloric was extricated; that a piece of it, 
when kept permanently ftretched, was fhortened by heat, 
and lengthened by cold ; and that an increaie of tempe¬ 
rature diminilhed its fpecific gravity. If it be ftretched 
in warm water, it retains its elafticity ; but if, when 
ftretched, it be placed in water colder than itfelf, it. 
remains diftended until heat be applied, when It again 
contracts. Hence it is concluded, “that the elafticity of 
caoutchouc depends on the caloric contained between its 
pores;” and that, if the caloric be removed from it, the 
elafticity is deftroyed. By diftenlion, the pore3 are forci¬ 
bly diminilhed, and a quantity of caloric is extricated ; 
while the affinity which exifts between the fubftance and 
8 S-- calorie 
