[ 718 ] 



LXXX. The Expansion and Thermal Hysteresis of Fused 

 Silica. By G. W. C. Kaye, B.A., D.Sc. The National 

 Physical Laboratory *. 



FUSED silica or quartz glass has assumed such importance, 

 and has been applied to so many purposes in physics 

 and chemistry, that a study of its thermal expansion may 

 perhaps be of general interest. 



As is well known, quartz, which in the crystalline state 

 has a considerable coefficient of expansion, assumes when 

 fused a smaller coefficient of expansion than that of any 

 other known substance, good invar alone excepted f. For 

 example, at ordinary temperatures the expansion coefficients 

 are 



quartz, || axis 7"5 X 10 -6 J 



„ 1 „ 13-7 „ 

 fused silica, c. 0*4 „ 



Owing to the extreme smallness of the expansion coefficient 

 of fused silica, most observers have adopted modifications of 

 Fizeau's interference method, more especially when for some 

 reason it was convenient to work with small samples. 



I. The Coefficient of Expansion. 



Moderate Temperatures. 



Chappuis and Scheel have each determined the coefficient 

 of expansion at moderate temperatures. Chappuis § (1903) 

 for the range 0° to 83° C. obtained the expression 



'° =(-385£-f-00115* 2 )l()- 6 , 



k 



where l t is the length at t°, l that at 0°. 



Scheel II in 1903 derived for the range 0° to 100° C. the 

 formula 



i^° =(-322* + -00147* 2 ) lO" 6 . 



In 1907H Scheel repeated his measurements with a new 



* Communicated by Dr. R. T. Glazebrook, F.R.S. 



t Invar is obtainable as such in three grades, covering a range of 

 coefficients of from about -0'3xl0-6 to +2-5x10 -6. 



X Benoit, Trav. et Mem. du Bur. Intl. i. 1881 ; vi. 1888. Scheel, 

 Ann. der Phys. ix. p. 837 (1902). Randall, Phys. Rev. xx. p. 10 (1905). 



§ Chappuis, Proces Verbaux, Inter. Comm. des Poids et Mesures, 1903, 

 p. 75. 



|| Scheel, Deut. Phys. Gesell. Verh. v. p. 119, March 1903. 



f Scheel, ibid, ix. p. 718, Dec. 1907 ; Zeit. Inst, xviii. p. 107 (1908). 



