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Caoutchouc Is foluble with cafe at a boilingheat in the exprefled vegetable oils, in wax,butter, and animal oil, forming vifcid unelafticcompounds.

Reftified oil of turpentine at the commontemperature a£ls without difficulty on caout-chouc, firft rendering it tranfparent and enlarg-ing its bulk confiderably, and in the courfe oftwo or three days effecting a compleat folution.The liquor is of the confidence of drying oil,and when fpread thin upon wood it forms avarnifh, which however is a long time in be-coming dry. When mixed with wax and boiledlinfeed. oil, it compofes an elaftic varnifh,which is ufed in coating balloons.

The only menftrua for this fubftance fromwhich it can be again feparated unaltered are,ether, petroleum, and cajeput-oil.

The folubility of caoutchouc in ether was firfldifcovered by Macquer , a circumftance which,from its frequent failure in the hands of otherehemifts, was very generally called in queftiontill Cavallo cleared up the difficulty, by fhowingthe neceffity of employing nvajhed ether for thispurpofe. If frefh made fulphuric ether is fliakenin a vial with an equal quantity of pure water,the fmall portion of acid which it generally con-tains is diffolved out by the water, and theether combines with about a tenth of its weightof this latter fluid. The waflied ether is readilyfeparated from die refidual water by decantationon account of its fuperior lightnefs, and is nowcapable of effedling a compleat and fpeedy fo-lution of caoutchouc. The folution is of a lightbrown colour, and when faturated is confider-ably vifcid. A drop of it let fall into a cup ofwater immediately extends itfelf over the wholefurface, and the ether being partly abforbed bythe water and partly evaporated, the water isfound covered with an extremely thin film ofcaoutchouc, poireffing its elafticity and all itsother characteriftic properties. A fimilar effecttakes place when cloth of any kind is foaked inthe folution, or any hard furface is fmeared overwith it; on expofure to the air the ether israpidly evaporated, and the caoutchouc whichit was combined with is left behind. The affi-nity of this folution for caoutchouc is very great:if the edges of two pieces of caoutchouc aredipped in it and immediately brought ill clofecontact with each other, as foon as the ether isevaporated they will be found to be perfectlyunited.

There are two circumftances which mull al-v- ' a Y s prevent tire extenfive ufe of the etheric' An. de Chun. xii. p

folution of caoutchouc, admirably qualified asit is in other refpefits for many ufeful purpofes;thefe are, firft, its expenfivenefs, and fecondly,the extraordinary rapidity with which the etherevaporates, thus rendering it impoffible to layan even coating of this varnifh on any furface,and clogging up the brufhes by which it is ap-plied. In order to form tubes or catheters ofthis fubftance, the beft method is to cut a bottleof caoutchouc into a long fingle flip, and foak itfor half an hour or an hour in ether: by thismeans it will become foft and tenacious, and ifwound dexteroufly in a fpiral form on a mould,bringing the edges in contact with each other atevery turn, and giving the whole a moderateand equal preffure by binding it with a tapewound in the fame direction as the caoutchouc,a very effectual union will be produced. Aftera day or two let the tape be taken off, and thecylinder of caoutchouc may be rendered flillmore perfect by pouring a little of the ethericfolution into a glafs tube clofed at one end, thediameter of which is a little larger than that ofthe cylinder of caoutchouc; which being intro-duced into the tube will force the folution tothe top of the veffel. Let the whole of theapparatus be then placed in boiling water, theether will be evaporated, and a fmooth and uni-form coating of newly depofited caoutchouc willremain upon the cylinder.

Petroleum when rectified by gentle diftillationaffords a colourlefs liquid not to be diftinguifhedfrom the pureft naphtha ; and this, according toFabroni, has the property of diflolving one-feventieth of its weight of caoutchouc, and ofdepofiting it again unaltered, by fpontaneous eva-poration. * It does not appear however that thismenftruum has been much employed.

The folubility of caoutchouc in- cajeput oilwas firft noticed by Dr. Roxburgh. f This isan eflential oil procured in India from the leavesof the Melaleuca Leucadendron , and promifes tobe the moft ufeful menftruum of this fubftancethat has hitherto been difcovered. The folutionis thick and very glutinous. When alcohol isadded, this latter unites with the eflential oil,“ and leaves the caoutchouc floating on the“ liquor in a foft femifluid ftate, which on being“ waflied with the fame liquor and expofed to“ the air, became as firm as before it was dif-“ folved, and retained its elaftic powers per-“ fe£Uy, while in the intermediate ftate between“ femifluid and firm, it could be drawn out into“ long tranfparent threads, refemhling in the“ polifh of their furface the fibres of the tendons

T A fiat. Refearohce, v. p. 167 .