14 Jackson and Rich, Solubility of Lead Glasses. 



In the foregoing experiments we have dealt with a 

 compound di-sihcate. It appeared to us the action of 

 HCI must be simpler in the case of di-silicate of lead, 

 Pb0.2SiO , in which the supposed insoluble pellicle must 

 be composed of silica. A piece of such a fritt was placed 

 in dilute HCI, and after a short time a white layer was 

 distinctly visible which was insoluble in the acid. We 

 also submitted a sample of commercial di-silicate to exami- 

 nation, by treating it with pebbles, in the manner already 

 described. The results are put out in the table below. 



These are quite in accordance with our previous 

 results. 



It had, however, repeatedly occurred to us that the 

 increase in solubility in all the before-mentioned experi- 

 ments migJit be entirely due to the increased fineness 

 caused by the grinding, as we have shewn in Part I. of 

 this paper that increase in fineness and of solubility go 

 hand in hand. 



With the apparatus at our disposal it was impossible 

 to directly test this, but it seemed most unlikely, considering 



