58 A. M. Mayer — Physical Properties of Vulcanite. 



Temp. 



Yol. of Mercury. 



Vol. of Vulcanite. 



Differences 



0° 



1-000000 



1-000000 



•oooooo 



10 



1-001803 



1-001845 



•000042 



20 



1-003610 



1-003740 



•000130 



30 



1-005421 



1-005685 



•000264 



40 



1-007236 



1-007680 



•000444 



50 



1-009055 



1-009725 



•000670 



60 



1-010878 



1-011820 



.000942 



70 



1-012705 



1-013965 



•001260 



80 



1-014536 



1-016160 



•001624 



90 



1-016371 



1-018405 



•002034 



100 



1-018210 



1-020700 



•002490 



As the apparent expansion of mercury in glass of a Fahr. 

 thermometer is '0000869 of its volume for 1°, and as the 

 apparent contraction of mercury in a vulcanite thermometer 

 is -00249 from 32° to 212°/ it follows that the length 

 of scale from 32° to 212° on a vulcanite thermometer 



-00249 



= ^^^^o^» = : ^8 0, 6 of length of scale on a similar mercurial 

 •0000869 & 



thermometer of glass. 



Kohlrausch states in his paper, cited above, that "the in- 

 crease of the coefficient of expansion of ebonite with the 

 temperature is very considerable. The linear expansion for 

 the temperature t can be put 



•000061 + -00000076 £." 



This formula agrees well with that which we determined for 

 the cubical expansion. Further on he says: "The solid ex- 

 pansion of ebonite is, from the above numbers, at 0° equal to 

 that of mercury ; at higher temperatures it is still greater. It 

 is possible that other kinds expand still more, so that as a curi- 

 osity a mercurial thermometer might be constructed whose 

 readings sink on being heated. " The great expansion may 

 possibly be connected with the proportion of sulphur which 

 ebonite contains : Kopp (Pog£\ Ann., vol. lxxxvi, p. 156) found 

 for the coefficient of sulphur -000061 at 30°. On the other 

 hand, the contrast to soft caoutchouc is very remarkable. I 

 will mention one fact which was observed in the observation of 

 expansion. The bar of ebonite, which was about one centi- 

 meter in thickness, after being heated required a considerable 

 time before it assumed a constant length. Although the bad 

 conductivity is doubtless the principal cause of this, I imagine 

 that another phenomenon is also at work. Like the elastic 

 change of form, the expansion by heat may also not take place 

 instantaneously, but continue itself after the change of temper- 

 ature, gradually becoming weaker. A few observations of 

 Matthiessen's with glass (Pogg. Ann., cxxviii,p. 521), seem to 



