724: 



Dr. G. W. C. Kaye on the Expansion and 



From the curve, one may derive the mean coefficient of 

 expansion over any desired range between — 190° and 1100° C. 

 The following values have been obtained from the original 

 curve which has been greatly. reduced in fig. 1. 



Temp. 



range. 



Expansion coefficient a. 



-100° 



to 



-120° C. 



-•43xl0" 6 



-120 



to 



- 80 



-•11 „ 



- 80 



to 



- 40 



+ •14 „ 



- 40 



to 







•31 „ 







to 



30 



•42 „ 



30 



to 



100 



•53 „ 



100 



to 



500 



•58 „ 



500 



to 



900 



■50 „ 



900 



to 



1100 



•80 ,. 



These results refer to clear, transparent, annealed silica. 

 It is probable that want of annealing is the cause in most 

 cases of the anomalous results which have been obtained by 

 some observers. This view is supported by the experiments 

 carried out in this Laboratory on the behaviour of specimens 

 subject to a first heating as contrasted with their behaviour 

 on subsequent heatings. 



In regard to the expansion of the translucent or satin-like 

 varietv of silica, information is forthcoming from some ex- 

 periments of Mr. A. Blackie at the National Physical Labo- 

 ratory, who has recently measured the relative expansions of 

 the two kinds of silica, the transparent and the translucent. 

 He finds that for temperatures below about 500° C. the 

 translucent variety expands slightly more than the transparent, 

 while for temperatures above 500° C. the reverse is true. 

 The difference, however, is very small, not more, for example, 

 than 30 parts in a million at 800 c . 



II. Change Points. 



It would appear from the expansion curve of fused silica 

 that it shows at least two change-points, one at about 1000° C. 

 the other at about —80° C. The former result agrees with 

 the conclusion of Day and Shepherd*, who showed that for 



* Day and Shepherd, Amer. Journ. Sci. xxviii. p. 1089 (1906). 



