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



traction is the same as that of the steel bar on which it rests, so 

 that vre have only to consider the length of the steel plate eqnal 

 to that of the vulcanite bar in computing the coefficient of 

 expansion of the vulcanite. Calling this length I, the distance 

 between the lines d, the coefficient of expansion of the steel 

 k, and the coefficient of expansion of the vulcanite e, we have 

 in the range of temperature t, 



d-^-l _ 



e = — — + h 



The mean of twelve determinations thus made between 0° C. 

 and 18° C. gave -0000686 as the mean coefficient in the above 

 range of temperature. 



The formula, of the cubical expansion of ebonite was 

 determined by a mercurial thermometer made of a bulb of 

 ebonite to which was attached a glass capillary tube 2. 

 of cylindrical bore, as shown in figure 2, the tube 

 of vulcanite was placed in a metal shield to pro- 

 tect it from moisture and it and the glass tube sur- 

 rounded with ice. The distance of the mercury from 

 a fine line engraved on the glass tube was read with a 

 cathetometer when the level of the mercury had 

 become stationary, and the lengths between the line 

 and the level of the mercury at different temperatures, 

 obtained by heating the apparatus in a hot air chamber 

 furnished with a thermostat, were measured. Know- f~ "" ^1 

 ing the capacity of the ebonite bulb and of a millime- ^ 

 ter in length of the glass tube we obtained the rate of 

 the apparent expansion, or rather, contraction of the 

 mercury, from which, after having allowed for the 

 expansion of the glass tube and the mercury in it, we 

 deduced the absolute expansion of the vulcanite. 

 The results of these experiments may be closely ex- 

 pressed in the following formula. 



V, = V + '000182Z + -00000025^ 



The formula of the cubical expansion of mercury 

 as given by Mendeleeff* is 



V t = V Q + -00O18OU + -000000O2£ 2 



It is thus seen that the cubical expansion of vulcan- 

 ite exceeds that of mercury so that the apparatus we 

 have described may be used as a thermometer in I j 



which, as Kohlrausch observed, the scale will be inver- ^-^ 

 ted ; when the temperature rises, the mercury in the stem falls. 



The following table gives the volumes of vulcanite and of 

 mercury at temperatures from 0° to 100°, as computed from 

 the above formulae. The difference, (in the fourth column),. 



*Jour. de Physique, v, p. 259. 



