GUTTA-PERCHA 773 



cord of a square, triangular, or hexangular, or any other form, bo required, the two 

 rollers must be shaped to suit. 



Gutta-percha Tubes. A series of interesting experiments have been made at the 

 Birmingham Waterworks, relative to the strength of gutta-percha tubing, with a 

 view to its applicability for the conveyance of water. The experiments were made 

 (under the direction of Henry Eose, Esq., engineer), upon tubes, and th of an inch 

 diameter, of gutta-percha. These were attached to the iron main, and subjected 

 for two months to a pressure of 200 feet head of water, without being in the slightest 

 degree deteriorated. In order to ascertain, if possible, the maximum strength of the 

 tubes, they were connected with the Water Company's hydraulic proving-pump, the 

 regular load of which is 250 Ibs. on the square inch. At this point the tubes were 

 unaffected, and the pump was worked up to 337 Ibs., but to the astonishment of every 

 one the tubes still remained perfect. It was then proposed to work the pump up to 

 500 Ibs., but it was found that the lever of the valve would not bear this weight. The 

 utmost power of the hydraulic pump could not break the tubes. 



The gutta-percha being somewhat elastic, allowed the tubes to become slightly 

 expanded by the extraordinary pressure which was applied, but on its withdrawal 

 they resumed their former size. 



This tubing is such an extraordinary conductor of sound, that its value, not only 



to deaf persons, but to the public generally, has been fully appreciated. It has been 



fitted up in dwelling-houses, in lieu of bells. As speaking-tubes for giving and 



receiving messages in mines, railway stations, prisons, workhouses, hotels, and all 



large establishments, it is invaluable. 



Properties of Common Gutta-percha. The gutta-percha, purified for manufacturing 

 purposes, is of a reddish brown colour ; it readily becomes electrical by friction and 

 is a bad conductor of both electricity and heat. At the ordinary temperature of our 

 climate, say from 32 to 77, it possesses about as much tenacity as thick leather, with 

 rather less flexibility ; it softens and becomes sensibly doughy towards 120, although 

 still very tough. Its ductility is such, at a temperature of from 110 to 241, that it 

 is readily extended into thin sheets, or drawn into threads or tubes ; its flexibility and 

 ductility diminish as the temperature becomes lower. It does not possess at any tem- 

 perature the peculiar elastic extensibility which characterises caoutchouc. Exposed 

 for an hour to a temperature of 14, its flexibility is slightly diminished. 



In its various forms, gutta-percha possesses a peculiar porosity, as may be shown 

 in the following manner : A drop of its solution in sulphuret of carbon is to be 

 placed on a glass slip ; the spontaneous evaporation soon reduces this solution to a 

 whitish plate ; if it be then examined with the microscope, the numerous cavities with 

 which it is pierced may be distinctly perceived. These cavities may be rendered 

 still more visi ble by means of a drop of water ; the liquid gradually insinuates itself, 

 the mass appears more opaque, and by means of the microscope the cavities are seen 

 to be enlarged. 



Similar results are obtained by keeping thin transparent laminae, obtained by the 

 evaporation, by heat, of a solution of gutta-percha, immersed in water for a considerable 

 time. 



The preceding observations lead us to think, that this substance retaining, in con- 

 sequence of its porosity, a great many minute particles of air, owes to this circum- 

 stance its appearance of possessing a less density than that of water, namely 0'979. 

 In fact, on stretching gutta-percha under strong pressure, and immediately cutting 

 the strips thus produced into very small pieces under water, the greater part of the 

 fragments fall to the bottom of the vessel some immediately, others after absorbing 

 a certain quantity of water. The same result is also obtained by keeping very thin 

 leaves of gutta-percha, prepared by different methods, immersed for a month in water 

 deprived of air : their pores becoming gradually filled with the liquid, they became 

 heavier than the water, and then ceased to float. Gutta-percha is also heavier in 

 proportion to the length of time it has been exposed to the air, particularly in thin 

 leaves. 



The porous structure of gutta-percha becomes changed into a fibrous texture when 

 it is drawn out so as to double its length : then retaining but little extensibility, it 

 supports, without breaking, the action of a force equal to double that required for its 

 elongation in the first instance. 



Common gutta-percha resists cold water, damp, and also the various influences 

 which excite fermentation ; but it can be softened, and it experiences a sort of superficial 

 doughy fusion by the action of the solar rays in summer. 



It is not attacked by alkaline solutions, even when caustic and concentrated ; am- 

 monia, saline solutions, water containing carbonic acid, the various vegetable and 

 mineral acids, do not act upon it ; the weaker alcoholic liquors (wines, beer, &c.) do 

 not touch it ; and even brandy scarcely dissolves a trace of it. Olive-oil does not 



