GIITTA PERCHA. This useful article is the produce of a very large and lofty forest tree called the Isonandra gutta, which is native in the islands of the Indian Archipelago. Some of its properties were first pointed out by Dr. W. Montgomerie in a letter to the Bengal Medical Board in 1843. When an incision is made in the bark of the above tree, a white substanc,e exudes which becomes shortly, by expo sure to air, hard and tough ; this is pure gutta percha. Neither the wood nor fruit of the tree appear to be of any great value ; and a full sized tree, when cut down and the gutta percha collected in bamboos, yields about 30 or 40 pounds of gutta percha.
Gutta percha is sometimes contaminated with organic matters, bits of bark, and foreign substances. To purify it, it is rasped in cold water, which removes the greater part of the soluble organic matters and salts, and also facilitates the removal of portions of wood and earthy matters, for gutta perCha does not combine with any substance of this kind, but merely holds it mechanically. The raspings are then washed and left to soak in warm water for several hours, and are fmally dried,heated to about 230°, and kneaded into lumps.
Gutta percha may be softened by hot water, and in that st,ate moulded into any form, stretched into sheets or straps, drawn out into tubes or threads, Sze., and on cooling completely it hardens and retains the form given to it. It does not possess at any temperature the peculiar elasticity of india-rubber.
Gutta percha resists the action of cold water and damp, and all those agents which promote fermentation. It is not acted on by alkalis, even when caustic and in their most concentrated form ; nor by ammonia, saline solutions, water containing carbonic acid, the various vegetable and mineral acids, and alcoholic liquors.
Olive oil dissolves a small portion of it when hot, but precipi tates it on cooling. Sulphuric acid with one equivalent of water
colours it brown, and disintegrates it with a sensible evolution of sulphurous acid. Hydrochloric acid attacks it slowly, and renders it brittle at a temperature of 68°. Monohydrated nitric acid attacks it rapidly, with effervescence and an abundant evolu tion of fumes of hyponitrous acid.
Only a small portion of gutta percha can be dissolved, even with the aid of heat, in absolute alcohol or ether. Benzole and spirits of turpentine dissolve it partially when cold, and nearly completely when hot. Sulphide of carbon, and chloroform, dissolve it completely when cold ; the solution becoming perfectly clear and almost colourless when filtered under a bell glass.
Gutta percha is sometiines vulcanized with sulphur, by a process patented by Mr. Hancock in 1847. It is sometimes treated with chloride of gine, The object of these processes is to give it a hard glazed surface free from stickiness. Vulcanized gutta percha may be varnished with a mixture of oil and resin, and polished till it acquirer the lustre of japanned wares.
Gutta percha is sometimes adulterated with the gums of otner trees, plaster of paris, &c.
It is an exceedingly valuable material for the baths and dishes used in photography, but when employed for these purposes should be scrupulously pure.
It has a porous texture, and its cells contain air. They may be clearly seen in a thin film of gutta percha placed under a powerful microscope.
Gutta percha is of great value to the surgeon for forming splints for fractured bones, since it can easily be nioulded to any shape when hot, and becomes sufficiently hard and rigid on cooling. It is also very useful for many surgical instruments.