408 Mr. T. Graham on the Absorption and 



mosphere passing into a vacuum, at the following rates per 

 square metre of surface : — - 



At 4° C, by 0"56 cub. centim. of air in 1 minute. 

 At 14° C, by 2*25 „ „ 



At 60° C, by 6'63 



The volumes of gas are all reduced to barom. 760 millims. and 

 therm. 20° C. 



Such numbers are probably not strictly constant; for it appears 

 that the effect of temperature upon rubber is much influenced 

 by the length of time that the temperature is continued, the 

 change in degree of softness with change of temperature requi- 

 ring hours, or even days, fully to complete it. The rigidity of 

 rubber- under cold and its softening under warmth are well 

 known to take place in a slow and gradual manner. 



With the softening of rubber by heat, the retentive power of 

 that substance for gases appears to be modified. Soft rubber, 

 first charged with carbonic acid at 20°, and then made rigid by 

 cold, appeared to lose its carbonic acid, when afterwards freely 

 exposed to air, less rapidly than the same rubber equally charged 

 but exposed from the first in its soft condition. The quantity 

 of carbonic acid retained in the former case was 10*76 per cent., 

 and in the latter 7*08 per cent, of the volume of the rubber, after 

 a similar exposure of forty-eight hours. This point, although 

 not sufficiently examined, is alluded to here on account of the 

 analogy which appears to hold between rubber and the malleable 

 metals in a power to absorb a gas when they are softened by 

 heat, and to retain the same gas with great tenacity when they 

 are afterwards made rigid by cold. 



The condensation of oxygen gas by masses of solid rubber 

 punched out of a block was made the subject of observation, by 

 placing 50 grms. of that substance within ajar of oxygen stand- 

 ing over mercury during a period of several days. From the 

 rubber afterwards there was extracted, by the action of a vacuum 

 continued for twenty-one hours, 6*21 cub. centims. of gas; of 

 which 367 cub. centims. were oxygen, 0*14 carbonic acid, and 

 the remainder chiefly nitrogen. Taking the bulk of the rubber 

 at 53'8 cub. centims., the oxygen absorbed amounts to 6*82 per 

 cent, of the volume of the rubber. Oxygen then may be re- 

 garded as fully twice as soluble in rubber as the same gas is 

 in water at the ordinary temperature. No experiment was made 

 at a higher temperature; but as the penetrativeness of rubber is 

 much increased by heat, the presumption is that the solubility 

 of gases in rubber is increased in the same degree. 



More than one attempt was made to identify the presence of 

 free hydrogen in the substance of rubber after being kept in that 



