A. M. Mayer — Physical Properties of Vulcanite. 55 



Hard-rubber, vulcanite, or ebonite, as it is variously called, 

 is formed of rubber and sulphur. These are combined in pro- 

 portions of about two parts of rubber to one of sulphur. These 

 ingredients, intimately mixed, are by the action of a temperature 

 of 300° F., lasting three hours, converted into a black com- 

 pound. The sun viewed through thin plates of this substance 

 appears of a deep red color. The hard-rubber used in our 

 experiments was formed of 64 parts of rubber of Para and 34 

 parts of sulphur. 



The coefficient of linear expansion was obtained with the 

 apparatus devised by me for this purpose and shown in the 

 accompanying figure. A plate of steel one meter long and 

 6 cm broad had a lug of steel 15 mm broad screwed on to its end 

 to act as an abutting piece against which the end of the bar of 

 vulcanite, 96 cm long 6 cm broad and l*3 cm thick, was pressed 

 hj means of springs, as shown in figure 1. A block of steel, 



l. 



carrying a tracer, while bearing against the end of the bar of 

 vulcanite was slid along the end of the bar and traced on the 

 surface of the steel bar a very fine line. The bars are in a 

 closed case in which they have remained for twenty-four hours. 

 The temperature is taken from thermometers lying on the 

 vulcanite bar. After having traced the line the apparatus is 

 placed in a metal case surrounded by ice and after the tempera- 

 ture has become stationary another line is cut by the tracer. 

 The bar in falling through the observed temperature has 

 shortened by the distance between the lines less the shrinkage 

 of the steel bar. The distance between the lines is measured 

 by a micrometer microscope. As the tracer is of steel its con- 



Tainter and myself, is so curious and suggestive that I give in full the arrange- 

 ment for studying the effect. When a sheet of hard rubber, A, was held as 

 shown in the diagram, the rotation of the disc or wheel B, interrupted what was 

 an invisible beam, which passed over a space of several meters before it reached 

 the lens C, which finally concentrated it upon the selenium cell D. A faint but 

 jjerfectly perceptible musical tone id as heard from the telephone connected with the 

 selenium that could be interrupted at will by placing the hand in the path of the 



invisible beam the effect is produced through two sheets of hard rubber 



having between them a saturated solution of alum. The anomalous behavior of 

 the hard rubber alluded to above suggested the thought of listening to it also. 

 This experiment was tried with extraordinary success. I held the sheet in close 

 contact with my ear while a beam of intermittent light was focussed ou it by 

 means of a lens. A distinct musical note was immediately heard. We found the 

 effect intensified by arranging the sheet of hard ruboer as a diaphragm, and 

 listening through a hearing tube.'' 



