162 Geological Society: — 



The two latter form a new class, coming to a maximum deviation 

 from their theoretical value at 45 per cent. 



In subclass a, specific heat — by reference to the Tables given, it 

 will be seen that the first addition of alcohol to water (though 

 alcohol has a specific heat much lower than that of water) produces 

 mixtures which have a higher specific heat than water, and that a 

 mixture containing between 30 and 40 per cent, alcohol has the 

 same specific heat as water. 



Similarly alcohol, though much more compressible than water, 

 yet, when added to it, forms mixtures less compressible than water ; 

 so that a mixture containing between 45 and 50 per cent, alcohol 

 has the same compressibility as water. 



The rate of expansion is remarkable, as, starting from water, it at 

 first is below the theoretical value, then rises ; at 17 to 18 per cent, 

 the rate of expansion is identical with the calculated expansion ; for 

 all mixtures stronger than this, the rate of expansion is constantly 

 above that calculated. 



The whole of the physical characters of mixtures of alcohol and 

 water come to a maximum deviation from their theoretical values 

 somewhere between 30 per cent, and 45 per cent, alcohol by weight. 

 The 30 per cent, nearly corresponds to the formula C 2 H 6 O + 6 O H 2 

 (=29'87 per cent.) ; the 45 per cent, has approximately the formula 

 C 2 H 6 + 3 O H 2 (=46 per cent.). 



Some of the physical properties examined seem to be especially 

 connected with each other ; these are : — 



1. Specific heat and heat produced by mixing ; for by dividing 

 the number of units of heat evolved by 5 grammes of any 

 mixture by 3*411, the elevation of the specific heat of such 

 mixture above the theoretical specific heat is obtained. 



2. Boiling-point and capillary attraction ; by dividing the depress 

 sionofthe capillary attraction by 3*6, the depression of the 

 boiling-point is obtained. 



Deville & Hoek have shown the specific gravity and index of re- 

 fraction to be connected with each other (Ann. de Chim. et de Phy- 

 sique, 3rd ser. vol. v. Pogg. Ann. vol. cxii.). 



Whether the relations thus established between the various phy- 

 sical properties of alcoholic mixtures hold good with other similar 

 substances, or whether these mixtures form a singular exception, 

 must be decided by further research. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 3/6.] 

 December 9th, 1868.— Prof. T. H. Huxley, LL.D., F.K.S., 

 President, in the Chair. 

 The following communications were read : — 

 2. " On the occurrence of Celestine in the Tertiary rocks of 

 Egypt," By H. Bauerman, Esq., E.C.S., and C. Le Neve Foster, 

 DJSc, F.G.S. 



This communication referred to the presence of celestine at two 

 different horizons in the Tertiary escarpment of Mokattam. The 

 beds forming the escarpment may be divided into two parts, namely; — 



