1884.] 



On the Electrical Qualities of Glass. 



495 



Specimen I. 



This glass contains (eliminating traces of lime and magnesia) 



80SiO 2 .15PbO.3K 2 O.2N-a 2 O, 



or with the qualification which applies in all the cases below, that 

 there is nothing to indicate the manner in which the silica is dis- 

 tributed among the bases, 



3{3(Pb0.4Si0 2 ) + (K 2 0.4Si0 2 )} + 2{3(Pb0.4Si0 2 ) + (Na 2 0.4Si0 2 ) } 



Found. Calculated . 



SiQ 2 57-25 56-6 



PbO 3813 38 57 



K>0 316 3-25 



Na 2 1-45 1-43 



99-99 99-85 



Specimen II. 

 22Si0 2 .5Pb0.2K 2 O.Na 2 0, 

 with elimination of traces of lime and magnesia ; or 

 2{5(Pb0.2Si0 2 ) + 3(K 2 0.4Si0 2 )} + {5(Pb0.2SiO,) + 3(Na 2 0.4Si0 2 )} 



Found. Calculated. 



Si0 2 48-56 49-15 



PbO 41-44 41-52 



K 2 7-76 701 



Na 2 2-25 231 



100-01 99-99 



Specimen III. 

 61Si0 2 .12Pb0.7K 2 0.2]S"a 2 ; 



or, 



7{2(K 2 0.3Si0 2 ) + 3(Pb0.3Si0 2 )}+2{2(N'a 3 0.3Si0 2 ) + 3(Pb0.3Si0 2 )} 



Found. Calculated. 



Si0 2 51-32 51-63 



PbO 37 88 38-31 



K,0 9-05 8-40 



Na 2 1-74 1-58 



99-99 99-92 



It is curious to note that this glass agrees very closely in composi- 



