706 



CAOUTCHOUC 



8. Plasticity. 



9. Facility of receiving every stylo of 



printing. 



10. Facility of being ornamented by 



painting, bronzing, gilding, ja- 

 panning, and mixing -with colours. 



11. Non-electric quality. 



12. Odour. 



1. Elasticity. 



2. Pliability. 



3. Durability. 



4. Insolubility. 



5. Unaltorability by climate or arti- 



ficial heat or cold. 



6. Inadhesireness. 



7. Impermeability to air, gases, and 



liquids. 



Mr. Burke, in describing his patented process, for the use of the golden sulphuret 

 of antimony, says, that he avoids two principal defects of the usual article, viz. its 

 efflorescence of sulphur with an offensive odour, and its consequent decomposition 

 and becoming rotten. He employs crude antimony ore (the sulphuret of that 

 metal, in fine powder), and converts it by boiling in water with soda or potash (carbo- 

 nates) into the orange sulphuret of that metal (Kermes mineral) by the addition of 

 hydrochloric acid to the fluid in slight excess. He combines this compound (after 

 being well washed) with caoutchouc or gutta-percha, either together or separately, 

 according to the degree of elasticity which he wishes to obtain. This mixture is 

 afterwards subjected to a heat of from 250 to 280 F. He masticates the caout- 

 chouc in the usual iron box, by means of the kneading fluted revolving rollers, sub- 

 jecting the whole to heat. The antimonial compound is then added in quantities 

 varying from 6 to 15 Ibs., according to the strength and elasticity required in the 

 compound. At the end of from one to two hours' trituration, the block is removed 

 from the box, and while in a warm state it is strongly compressed in an iron mould ; 

 and after being under pressure for a day or two is subjected to a steam heat for a 

 couple of hours. The block thus prepared may now be cut into sheets, and afterwards 

 divided into threads, or formed into such other articles as are desired. This forms 

 the elastic red rubber. 



The chief improvements operated in caoutchouc by the process of vulcanisation are 

 the properties of resisting and remaining unaffected by very high degrees of heat and 

 cold, and increased compressibility and elasticity. In its natural state India- 

 rubber becomes rigid by exposure to cold, and soft and plastic by heat, or under the 

 action of boiling water. Articles manufactured of this substance suffer and lose the 

 qualities which constitute their value in cold and in hot countries. A piece of India- 

 rubber cloth, for instance, taken to Moscow in December or January, would assume 

 all the qualities of a piece of thin sheet iron, or thick pasteboard ; the same cloth 

 would in India or Syria become uncomfortably pliable, and present a moist and greasy 

 appearance ; and, indeed, after being folded up some time, would be found to be glued 

 together. Nothing but vulcanisation insures the equable condition of the articles in 

 the most intense cold, and, in heat up to and above 300, makes India-rubber fit for 

 practical purposes. These advantages have conduced to its being very extensively used 

 in connection with machinery of every description ; and as steam power is still further 

 employed, and as the numerous other advantages possessed by vulcanised India-rubber 

 become known (for it is only of late that any idea of their extent has been realised) 

 its application will be extended and its consumption proportionally increased. 



The compressibility and the return to its former dimensions, when the pressure has 

 ceased, in one word, the elasticity of the India-rubber, is increased to such a degree 

 by vulcanisation, that comparing the improved with the original article, it may be 

 said that the native India-rubber is almost devoid of elasticity. The high degree of 

 elasticity which it obtains by vulcanisation is shown by the results of the following 

 experiments, in which a block of the vulcanised India-rubber, of the kind used for 

 the manufacture of railway carriage springs, measuring 6 inches outside disc, 1 inch 

 inside disc, and 6 inches deep, was taken and exposed to pressure : 



A pressure of 4 ton reduced it to 

 1 



14 

 2 



a* 



3 

 34 



The block was left under pressure for 48 hours, and in each case returned to its 

 original dimensions after a short period when the pressure was removed. 



Among the most recent uses of India-rubber and canvas, are those of its manu- 

 facture into gas and ballast bags, the former are used for the transport of gas, and 



