78 



Table 54. 

 ELASTICITY OF CRYSTALS. 



Some particular values of the Elastic Moduli are here given. Under E are given moduli for extension or compression 

 in the directions indicated b)f the subscripts and explained in the notes, and under T the moduli for torsional 

 rigidities round the axes similarly indicated. 



(a) Regular System.* 



Substance. 



Fluor spar 

 Pyrites . 

 Rock salt 



Sylvine . 



Sodium ch 

 Potash alum 

 Chrome alum 

 Iron alum . 



oride 



1473 X i°® 

 3530 X 106 

 419 X 10^ 

 403 X 106 

 401 X lo^ 

 372 X 10^ 

 405 X io« 

 181 X 108 

 161 X 10'' 

 186 X 106 



1008 X 10^ 

 2530 X 106 

 349 X 10*5 

 339 X 106 

 209 X 10^ 

 196 X lo^ 

 319 X io« 

 199 X lo" 

 177 X 108 



910 X 10^ 



2310 X 10^ 



303 X 106 



345 X 106 



1075 X 106 



129 X 10^ 



655 X 106 



Authority. 



Voigt.t 



Koch.t 



Voigt. 

 Koch. 

 Beckenkamp.] 



(d) Rhombic System.]! 



Substance. 



Barite 

 Topaz 



El 



620 X 10^ 

 2304 X 10^ 



E, 



540 X 10^ 

 2890 X 10® 



959 X io« 

 2652 X lo^ 



E4 



376 X io« 

 2670 X 10® 



702 X 10® 

 2893 X 10® 



Ee 



740 X 10* 

 3180 X 10® 



Authority. 



Voigt. 



Substance. 



Barite 

 Topaz 



Ti.-T,, 



283 X 10® 

 1336 X io« 



1*1 3 — T3 



293 X 10® 

 1353 Xio« 



T,., = T, 



121 X 10^ 



1104 X lo® 



Authority. 



Voigt. 



In the MoNOCLiNic System, Coromilas (Zeit. fiir Kryst. vol. i ) gives 

 Emai = 887 X 10® at 21.9° to the principal axis. 

 £„,„ = 313X106 at 75.4° 

 Em„ = 2213 X 10® in the principal axis. 

 Emin = 1554 X 10® at 45° to the principal axis. 



Gypsum j 



Mica 



In the Hexagonal System, Voigt gives measurements on a beryl crystal (emerald). 



The subscripts indicate inclination in degrees of the axis of stress to the principal axis of 



the crystal. 



£0 = 2165X106, £45 = 1796X106, £90=2312X106, 



To= 667X106, T9o = 883X106. The smallest cross dimension of the 



prism experimented on (see Table 82), was in the principal axis for this last case. 



In the Rhombohedric System, Voigt has measured quartz. The subscripts have the 

 same meaning as in the hexagonal system. 



£0=1030X106, £_45= 1305X106, £+45 = 850X106, £90 = 785X106, 



To = 508 X 1 o«, T90 = 348 X 1 06. 

 Baumgarten 1[ gives for calcspar 



£0=501X106, £_46 = 44iXio6, £ + 45 = 772X106, £90 = 790X106. 



* In this system the subscript a indicates that compression or extension takes place_ along the crystalline axis, and 

 distortion round the axis. The subscripts i and c correspond to directions equally inclined to two and normal to the 

 third and equally inclined to all three axes respectively. 



t Voigt, " Wied. Ann." vol. 31, 34-35 ; 36, 642. 



t Koch, "Wied. Ann." vol. iS. 



§ Beckenkamp, "Zeit. fiir Kryst." vol. 10. 



II The subscripts i, 2, 3 indicate that the three principal axes are the axes of stress ; 4, S, 6 that the axes of stress 

 are in the three principal planes at angles of 45° to the corresponding axes. 



H Baumgarten, " Pogg. Ann." vol. 152. 



Smithsonian Tables. 



