10 Jackson and Rich, Solubility of Lead Glasses. 



the free condition, or a glassy compound possessing the 

 composition of the dissolved material is present. The 

 formula for such a compound would contain 3 molecules 

 of basic oxides to I of acid oxides, whereas, according to 

 Benrath, a normal glass is taken to possess exactly the 

 reverse proportion between bases and acids. 



Then again, in the case of a compound showing so high 

 a solubility as 8'24 per cent, (the solubility of di-silicate of 

 lead as mentioned later) one would expect that, if the 

 soluble matter is extracted from the whole mass of the 



compound, and not from its surface only, there would 

 occur some change in its ph}-sical condition. The par- 

 ticles would either become porous or they would be 

 disintegrated. Neither of these effects was apparent after 

 the action of the acid on the compound, which remained, 

 in these respects, unaltered. 



We therefore submitted the idea of the existence of 

 this insoluble siliceous coating to the test of experiment. 

 Two lines of attack suesfested themselves to us 



