206 Mr. T. Gray. 



The mean of which would give — 



Potash 

 Soda. . 

 Lime. . 

 Silica . 



9-2 

 6-5 

 11 '3 

 73 -0 



The alkali is therefore sJightly in excess, but to compensate that r 

 there is an excess of silica, the result being a very good glass, both 

 chemically and electrically. 



Specimen VII. (Arsenic-enamel glass.) 



49 c 

 105 

 115 

 125 

 135 



C 



140 x 10 13 ? 

 230 x 10 11 

 101 x 10 11 

 45 x 10 11 

 22 x 10 11 



3-07 



Silica 54 



Lead oxide 23 



Potash \ 17 : ( .... *10 

 Soda J I.... * 7 



Lime 



Magnesia . . . , 



Iron and manganese 



oxide and alumina 

 Arsenic oxide by diff. 3 



100 -o 



In this glass we have an excess or alkali for the lead oxide, and a 

 deficiency of silica; the composition is rendered complicated, how- 

 ever, by the presence of the arsenic. 



Specimen VIII. (Thomson's 



electrometer jar.) 





100° C. .. 206 xlO 12 .. 3 172 .. 





55 -18 



120 .. 468xlO n .. .. 





31 01 



140 .. 106 xlO 11 





13 '28 



160 .. 245 xlO 10 





0-35 



180 .. 56 xlO 10 



Magnesia 



0-06 



200 .. 12 xlO 10 



Alumina, iron and 





manganese oxides. 



0-67 







100 -55 



The formula PbO,K 2 0,Si0 2 , gives— 



6 









53-2 







32 -9 







13-9 





Katio of potash to soda may be too high. 



