GUTTA-PERCHA 775 



the sides of the tube. These points, which become gradually larger, are formed of 

 crystalline tufts of the white resin. Thus this proximate principle is separated directly, 

 and in the cold, even when the atmospheric temperature is gradually rising, for in- 

 stance during the spring or early summer. 



The crystalline white resin, when completely purified by washings with alcohol, and 

 then redissolved in anhydrous alcohol, is deposited by slow spontaneous evaporation in 

 the air, in radiated crystals, forming sometimes symmetrical tufts arranged in stars, 

 and then presenting the appearance of a sort of efflorescence. 



Distinctive characters and properties of the three proximate principles which con- 

 stitute common Gutta-percha. The most abundant of these three principles, forming 

 at least from 75 to 82 per cent, of the whole mass, is the pure gutta-percha, which 

 presents the principal properties of the commercial substance ; it is white, transparent 

 at a temperature of 212 F., when all its parts are melted together ; opaque or semi- 

 transparent when cold, from its then acquiring a structure which causes the inter- 

 position of air, or of a liquid possessing a different refraction from its own. This 

 structure appears still more distinct than in the natural substance containing all three 

 principles. 



In thin sheets, and at a temperature of 50 to 68 P., it is supple, tough, extensible, 

 but not very elastic. At 112 F., it softens and turns back upon itself, and becomes 

 more and more adhesive and translucent in proportion to the elevation of temperature, 

 undergoing a sort of doughy fusion, which becomes more distinct towards 212 to 

 230. Heated beyond this point, it melts, boils, and distils, furnishing a pyrogenous 

 oil and carburetted gases. 



Soubeiran believes the composition of perfectly pure gutta-percha to be C 12 H 10 , cor- 

 responding to 87'8 carbon and 12*2 hydrogen. Faraday found caoutchouc to contain 

 87'2 carbon, 12 '8 hydrogen ; hence their chemical composition is identical. 



Pure gutta-percha, like the other two proximate principles, is quickly rendered elec- 

 trical by friction, and is a bad conductor of heat ; it generally floats on water, but 

 sinks to the bottom as soon as its pores are filled with this liquid. It is insoluble in 

 alcohol and ether, almost completely insoluble in benzine at 32 F. ; it is soluble at 

 77, and becomes more and more so in proportion as the temperature is raised. The 

 saturated solution at 86 forms itself into a semi-transparent mass when cooled below 

 32 ; alcohol precipitates the pure gutta-percha from its solution in benzine. 



At 82, spirits of turpentine dissolves very little gutta-percha, whilst it disinte- 

 grates and dissolves it readily when hot. 



Chloroform and sulphide of carbon dissolve gutta-percha in the cold. 



After the extraction by means of ether of the two resins interposed in the thin 

 leaves of the white gutta-percha, leaving the last portion of ether with which they were 

 impregnated to evaporate in the open air, these leaves, enclosed in a flask, experienced, 

 after remaining there for two months at a temperature of from 68 to 82 F., an 

 alteration which appeared to depend on their porosity, the action of the air, and per- 

 haps the ether retained in their pores. However it be, these leaves had then acquired 

 new properties ; they were brittle ; exhaled a very distinct sharp odour ; brought into 

 contact with an excess of anhydrous ether, they were partially dissolved ; the soluble 

 portion, obtained by the evaporation of the ether and dessication at 194 F., was gluti- 

 nous and translucent ; it became opaque and hard by cooling down to 14 F. 



Sulphide of carbon, renewed three times in six days, arid evaporated each time after 

 two days' contact, left as residue a white flexible leaf. The portion not dissolved, 

 swelled and transparent, did not appear to undergo 'any change when left in sulphide 

 of carbon for ten days. 



This kind of spontaneous transformation would perhaps become complete if more 

 prolonged ; its study will require much time ; it will perhaps put us in the way of as- 

 certaining the causes of certain changes observed in some small objects formed of gutta- 

 percha. It has already been ascertained, that thin leaves, exposed for eight consecutive 

 days to the action of the sun in moist air, were discoloured, and that their substance 

 had become in great part soluble in ether. 



Monohydrated sulphuric acid disintegrates, and communicates a brown colour to the 

 pure gutta, with evolution of sulphurous acid; after eight days' contact, the deep 

 brown liquid, on dilution with water, becomes turbid, and furnishes a brown flocculent 

 precipitate. Nitric acid, with a single equivalent of water, attacks the pure gutta with 

 a lively effervescence, and the evolution of orange-vapours of hyponitrous acid. Mu- 

 riatic acid, in its saturated solution, slowly attacks the thin leaves of gutta, giving 

 them a deep brown colour ; at the end of eight days it becomes friable. The reaction 

 of muriatic acid establishes an additional distinctive character between this proximate 

 principle and the two others. 



M. Payen has carefully examined the chemical and physical peculiarities of the 

 three principles which he has discovered in gutta-percha. These have, however, 



