744 C A O 
CA'O-YANG, a town of Afia, in the kingdom of Co¬ 
rea, feven miles north-weft of King-kitao. 
CA'O-YUEN, a town of China, of the third rank, in 
the province of Chang-tongj forty-two miles north-weft 
of Tcin-tcheon. 
CAO'RLA, a town of Italy, on an ifland of the fame 
name, in the Gulf of Venice, near the coaft of Friuli ; the 
fee of a Bifhop, fuffragan of Venice. Lat. 45. 34. N. Ion. 
30. 30. E. Ferro. 
CAOUTCHOUC' (Indian), the Elastic Resin, or 
India-Rubber,/. A fubftance produced from the Iatro- 
$a clafiica, which grows fpontaneoully in Guiana, Quito, 
Jlrafil, Cayenne, and other parts of South America. No 
Fubftance is yet known which is fo pliable, and at the fame 
time fo elaftic. From the account of M. de la Conda- 
mine, we learn that this fubftance oozes out, under the 
form of a vegetable milk, from incifions made in the tree; 
and that it is gathered chiefly in time of rain, becaufe, tho’ 
it may be collecled at all times, it flows then moll abun¬ 
dantly. The means employed to inlpilfate and indurate 
it, M. de la Borde fays, are kept a profound fecrer. M. 
Romare, and others, affirm, that it thickens and hardens 
gradually by being expofed to the air; and as foon as it 
acquires a folid confidence it manifefts a very extraordina¬ 
ry degree of flexibility and elafticity. Accordingly tire 
Indians make boots of it, which water cannot penetrate, 
and which, when fmoked, have the appearance of real 
leather. Bottles are alfo made of it, to the necks of which 
are faftened hollow reeds, fo that the liquor contained in 
them may be fquirted through the reeds or pipes by pref- 
fuie. One of thefe filled with water is always prefented 
to each of the gue'ts at their entertainment, who never 
fail to make ufe of it before eating. This whimfical cuf- 
.tom led the Portuguefe in that country to call the tree 
that produces this relin pao dixirringa, and lienee the name 
of feringat was given both to the tree and its relinous pro¬ 
duction. Flambeaux, an inch and a half in d'aineter, and 
two feet long, are made of this relin, which give a beauti¬ 
ful light, have no bad fmell, and burn twelve hours.- A 
kind of cloth is alfo prepared from it, which the inhabi¬ 
tants of Quito apply to the lame purpofes as our oil-cloth 
and fail-cloth. It is formed, by means of moulds, into a 
■variety of figures for ufe and ornament, by the following 
procefs : The juice, when immediately taken, is fpread 
over pieces of clay formed into the delired ftiape ; and, as 
fall as one layer is dry, another is added, till the fabric be 
of a proper thicknefs : the w hole is then held over a ftrong 
fmoke of vegetables on fire, whereby it hardens into the 
texture and appearance of leather ; and before the finilh- 
ing, while yet foft, is capable of having any impreflion 
made on the outiide, which remains ever after. 
Ever fince this relin has been known in Europe, its che¬ 
mical qualities and other interefting properties have been 
very diligently inveftigated. In particular, it has been 
endeavoured to difeover lorne method of diffolving it in 
fuch a manner that it would affume difFeient figures with 
equal eafe as when in its original ftate of milk. In the 
memoirs of the academy of Sciences for 1768, we have an 
account of feveral attempts for this purpofe. The ftate 
of vegetable milk, in which the caoutchouc is found, when 
k comes from the tree, led Mr. Macquer to imagine that 
if was compofed of an oil and a w atery matter. From its 
wanting aromatic flavour, from its little volatility, and 
from its being incapable of folution in fpirit ot wine, he 
concluded that the oil which entered its-compofition was 
not an effential, but a fatty, one. Hence he thought it 
probable that it palled from a fluid to a folid form by the 
evaporation of the watery part, and that the oily folvents 
would reduce/t to a foft ftate. The firlt trials he made 
for diflblvuigar were with lihfeed oil, effence of turpen¬ 
tine, and feveral others. But all he could obtain by means 
of thefe menftrua was a vifeid fubftance, incapable of be¬ 
ing hardened, and totally void of elafticity. The recti¬ 
fied elfential oil of turpentine was employed feemingly 
with,greater fuccefs. To feparate from this menftrutim 
C A O 
the caoutchouc which it had diflolved, Mr. Macquer ad¬ 
ded fpirit of wine; but the confequence was, that part 
only of the oil united with the fpirit ; the reft remaining 
obftinately attached to the refin which it had diffolved, 
and thus preventing it from aflfuming a folid confiftence. 
From the great volatility of ether, he was next induced 
to try it as a menftruum ; and, for this purpofe, he pre¬ 
pared fome with great attention. The caoutchouc, cut 
into little bits, and put into a proper veffel with as much 
ether as was fufficient to cover it, was perfectly diffolved 
without any other heat than that of the atmofphere. This 
folution was tranfparent and of an amber colour. Upon its 
being thrown into water, no milky liquor was produced ; 
but there arofe to the furface a folid membrane which pof- 
feffed the great elafticity and other peculiar properties of 
the caoutchouc. The diftinguifhing properties of this fub¬ 
ftance, viz. its folidity, flexibility, and elafticity, and its 
quality of refilling the aClion of aqueous, fpirituous, faline, 
oily, and other common folvents, render it extremely fit 
for the conftruClion of tubes, catheters, and otherinftru- 
ments, in which thefe properties are wanted. In order to 
form this refin into fmall tubes, Mr. Macquer prepared a 
folid cylindrical mould of wax, of the defired fize and 
ftiape ; and then, dipping a pencil into the etherial folution 
of the refin, daubed the mould over with it, till he had 
covered it with a coat of refin of a fufficient thicknefs. 
The whole piece is then thrown into boiling water, by 
the heat of which the wax is foon melted, and rifes to the 
furface, leaving the refinous tube completely formed behind. 
To thefe experiments of Mr. Macquer, fucceeded thofe 
of M. Groflart (Chilly) ; whence a folution of the caout¬ 
chouc, by the fimple operation of boiling-water, has been 
difeovered, and a more eafy mode of forming catheters, 
tubes, &c. for medical and furgical ufes. The experiments- 
and procefs the author ftates as follows : “ Experience has- 
Ihewn me, that, a ftrong prefTure made upon two united 
pieces of caoutchouc, when brought to a ftate of fotmefs, 
and the weight continued until they are entirely dry, cauf— 
ed them to contract (o ftrong an adhefion, that the piece, 
being pulled out till it broke, often broke, not at the 
united part, but by the fide of it. By means of ether I 
immediately fucceeded in making thefe tubes. The me¬ 
thod which appears fo me to fncceed the beft, is to cut a-, 
bottle circularly in a fpiral flip of a few lines in breadth. 
It is very eafy to cut a long bottle in fuch a manner as to 
form a Angle long flip, and thus unneceftary joinings are 
avoided. The whole flip is to be plunged into ether, un¬ 
til it is fufficiently foftened, which comes to pafs fooner 
or later according to the quality of the vitriolic ether that 
is employed. Half an hour frequently fuffices. The flip 
being then taken out, one of the extremities is to be taken 
hold of and rolled, firft upon itfelf at the bottom of.the 
tube, prefling it ; then the rolling is to be continued, 
mounting fpirally along the mould, and taking care to lay 
over and comprefs with the hand every edge, one againft 
the other, fo that there may not be any vacant fpace, and 
that all the edges may join exaflly. The whole is to be 
bound hard with a tape of an inch in width, taking care 
to turn it the fame way with the flip of elaftic gum. The 
tape is to be tied up with packthread, fo that, by every 
turn of the packthread joining one another, an equal pref- 
fure is given to every part : it is then left to dry, and the 
tube is made. The bandage is to be taken off with great 
care, that none of the outward furfaces, which may-have- 
been lodged within the hollows of the tape (of which the 
caoutchouc takes.the exaft impreflion), may be pulled a- 
way. It is eafy to take off the tube of elaftic gum which 
has been formed upon a folid mould of one piece ; if the 
mould be made rather conic, it may be made to Aide off 
by the fmaller end ; at the worft, it is eafily accomplifhed 
by plunging it into hot water; for it is foftened by the 
heat, and is diftended ; without this precaution it would 
be fometimes difficult to draw it off when dry, becaufe,, 
having been applied upon the mould whilft it had its vo¬ 
lume. augmented by the interpofition of the ether, the: 
5 P ar£s ' 
