MECHANICS AND USEFUL ARTS. 97 



important changes in many of its characteristic properties. It is no 

 longer affected by climatic temperature ; it is neither hardened by cold 

 nor softened by any heat which would not destroy it. It ceases to be 

 soluble in the common solvents of caoutchouc, while its elasticity 

 becomes greatly augmented and permanent. The sarne effect may be 

 produced by kneading sulphur into caoutchouc, by means of powerful 

 rollers ; or the common solvents, naphtha and spirits of turpentine, may 

 be charged with a sufficient amount of sulphur in solution to become a 

 compound solvent. A vulcanized solid sphere, of two and a half inches 

 in diameter, when forced between two rollers a quarter of an inch apart, 

 was found to maintain its form uninjured ; in fact, it is the exclusive 

 property of vulcanized caoutchouc to be able to retain any form impressed 

 upon it, and to return to that form on the removal of any disturbing 

 force which has been brought to bear upon it. Caoutchouc slightly 

 expands and contracts in different temperatures ; it is also capable of 

 being condensed under pressure. A tube of two and a quarter inches, 

 impactly secured, was subjected to a force of 200 tons ; the result was 

 a compression amounting to one tenth. Great heat appeared to have 

 been evolved ; and the excessive elasticity of the substance caused a 

 fly-wheel, weighing five tons, to recoil with an alarming violence. The 

 evolution of heat from caoutchouc, under condensation, is a property 

 possessed by it in common with air and the metals ; it differs from the 

 latter, however, in being able to exhibit cold by reaction. Mr. Brocke- 

 don stated, that he had raised the temperature of an ounce of water 

 two degrees in about 15 minutes, by collecting the heat evolved by the 

 extension of caoutchouc thread ; he refers the heat to the change in 

 specific gravity. He contends that this heat thus produced is not due 

 to friction, because the same amount of friction is occasioned in the 

 contraction as in the extension of the substance, and the result of this 

 contraction is to reduce the caoutchouc thus acted upon to its original 

 temperature. 



Among the recent applications of the elastic force of caoutchouc, 

 attention was directed to the application of tubes of vulcanized caout- 

 chouc as torsion springs to roller blinds, adjusted to the heaviest exter- 

 nal blinds of houses, or the most delicate carriage-blinds ; and equally 

 applicable to clocks and various machines as a motive power. To the 

 raising of weights, (Hodges' patent application,) short lengths of rubber, 

 termed power-purchases, are successively drawn down from, or lifted 

 to, a fixed bearing, and attached to any weight which it is required to 

 raise. When a sufficient number of these power-purchases are fixed 

 to the weight, their combined elastic force lifts it from the ground. 

 Thus, ten purchases of the elastic force, of 50 pounds each, raise 500 

 pounds. Each purchase is six inches long, and contains about one and 

 a half ounces of vulcanized caoutchouc. These ten purchases, if stretched 

 to the limit of then- elasticity, not of their cohesive strength, will lift 

 650 pounds. This power the accumulation of elastic force though 

 it obeys the common law of mechanical powers, differs enough to be 

 distinguished as a new mechanical power. 



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