On the Variation of the Electrical Resistance of Glass, fyc. 205 



Apparently the best glass has the formula — 



r Silica 75-3 



CaO,NaoO,Si02= < Lime 117 



e I Soda 13'0 



100 -o 



" If this is deviated from an increase in the proportion of soda to 

 lime requires a considerable increase in the proportion of silica to base. 

 The flask is therefore defective, for not only is the soda in excess to 

 the lime, but the silica is deficient. I calculate that from 20 to 25 

 parts of silica should be added to 100 of that glass to counteract the 

 excess of soda. Such a glass would be — 



Silica 77'5 



Lime 9 *5 



Soda 13-0 



" However, too little is yet known of the relations of composition to 

 quality of glass to admit of positive statement. 



"The empirical formula ajCaO,Si0 2 + 2/Na 2 0,Si0 2 seems to me 



to be a tolerably accurate expression of the various kinds of good glass, 

 provided x and y are not very different from one another. When 

 equal, the glass is certainly excellent." 



Specimen VI. 



66 c 

 88 

 110 

 132 

 150 

 170 

 193 



C. 



497 xlO 11 

 828 xlO 10 

 138 x 10 10 

 230 x 10 9 

 540 x 10 8 

 147 x 10 8 

 308 x 107 



(Bohemian beaker.) 

 587 



Silica 75-65 



Lime 8 '48 



Potash 7'92 



Soda 6-92 



Magnesia '36 



Alumina, iron and 



manganese oxides. 70 



100 '03 



Assuming the formula K 2 0,CaOSi0 2 + Na 2 0,CaO,Si0 2 , as giving 



the best composition, we should have • 



Potash 

 Lime. 

 Silica, . 



18 "4 



11 -o 

 70 -6 



Soda. 

 Lime 

 Silica 



13 -0 

 11 7 



75 -3 



