408 



Professor T. E. Thorpe 



[May 4, 



Table showing that the amount of lead oxide dissolved from a fritt by ■ 25 

 per cent, hydrochloric acid does not depend simply upon the amount of 

 silica in the fritt. 



I — Solubility practically the same ; amounts of silica very 

 different. 



Fritt B 101 .. 



Boch's fritt 

 Fritt B 102 .. 

 Maastricht fritt 

 Fritt B 3 



II. — Solubilities Tery different ; amounts of t-ilica approximating 

 to equality. 



A remarkable illustration of this fact is to be seen in the case 

 of flint glass, which is substantially a double silicate of lead and 

 alkali. It is practically unacted upon by dilute acids, yet each of its 

 proximate constituents — lead silicate and alkali silicate — is readily 

 attacked. 



The second consideration, which seems to affect, the ease with 

 which lead is yielded to solvents, is complete chemical union. Merely 

 to flux together the ingredients of a fritt, with no regard to its com- 

 position as a definite chemical compound, and with no regard to the 

 time or temperature needed to complete the chemical changes for the 

 formation of chemical compounds, is not the proper way to make a 

 fritt. The analogy of the practice of the glass workers may again 

 be quoted in support of this fact. 



But I think I can offer, in addition, direct chemical testimony from 

 a study of the fiitts themselves. I found, very early in the course of 

 the inquiry, that the Continental fritts, which conformed to the ratio 

 and were distinguished by their comparative insolubility, were very 

 difficult to break up by the action of strong acids, and yielded only 

 relatively minute portions of soluble matter, much of which, however, 



