Microseojyical Shidy of the Belgian Rocks. ByA.Benard. 215 



result a temperature of 307° C* By studying the rate of ex- 

 pansion of the Hquid, Sorby concluded that the quartz in the 

 trachyte of Ponza must have been formed at about 356° C, which 

 may be looked upon as a very similar temperature. The number 



* The volume of the liquid cavity (an ellipsoid of revolution) is ^irah'^, 



a = 0,mm,00482 



h = 0,OTm,00330 



6* = 0,00001089 



«62 = 0,0000000524898 



- IT = 4,1887901 

 o 



4 



E = -7ra6^ = 0/n?>ic,0000002 198687 



4 

 Bubble formula, - ir r* 



r = 0,00093 



4 



L = - TT r' = 0mmc,000000003429 



Volume of the cube, c = 0«imc,0000000098003 



For the relation of the weight to the volume, we have the following formula : 

 Water, P = V x 1000 ; for any given body, P = V X 1000 x specific gravity. 

 In the»e formulse, when V represents cubic metres, P denotes kilogrammes. Conse- 

 quently if V denotes cubic millimetres, P represents thousandths of miiligrammea. 

 Hence 



V = ^ 



1000 X specific weight 



p denoting the weight of water contained in the cavity, oj the weight of the salt 

 (without the cube), we have at the temperature of these micrometric determina- 

 tions, and admitting that in the solution of salt there is neither augmentation nor 

 diminution of the total volume, 



iL + IOOOT-2X6 = E - (L + C) = 0,000000206644 [.] 



2,26 is the density of salt at 0° ; at 20°, the temperature at which the micrometric 

 measurements were made, this density is less than the zero-value by some 

 thousandths. We have neglected this slight variation. A similar allowance 

 must also be made for the water. According to Eegnault (' Chimie,' t. i. p. 456, 

 table), at 0°, 100 grammes of water contain, when saturated, 35,5 grammes of 

 salt; at 120°, 100 grammes of water, when saturated, 40,5 grammes of salt. 



Moreover, the solubility increases in proportion to the variation of temperature ; 

 this gives an increase of y|^ grammes of salt for a variation of 1°. Consequently, 

 at 20°, 100 grammes of water contain 35,5 grammes of salt + fs ; that is, 36,33 

 grammes. 



We have then the equation, 



CO 36,33 



p ~ Too" ■ 



By representing the weight of the cube by q, and the temperature at which 

 the cavity was formed by t, 



35,5 + ^ 

 u+J _ 24 



p ~ Too t'^^ 



m>^i The 



[6] 



