8 Jackson and Rich, Solubility of Lead Glasses. 



Since we have shown that solubiHty in weak acid and 

 fineness are intimately connected, it is essential that details 

 of the solubility of a glaze or fritt should be accompanied 

 by particulars enabling a judgment to be formed as to its 

 fineness. 



II. The Formation of an insoluble Coating on Particles of a 

 Lead Fritt during the action of dilute Liydrochloric 

 A cid. 



That an apparently maximum solubility is always 

 reached after shaking a lead fritt with acid a short time, 

 points to the existence of a factor, other than fineness of 

 the particles, affecting the action ; and this may be the 

 formation of an insoluble layer of silica or other compounds 

 on the surface of the particles. 



Dr. Thorpe states that a fritt by treatment for one 

 hour with dilute hydrochloric acid yields to the solvent 

 the whole of its soluble lead oxide, with the exception of 

 the merest trace, approximately o'l per cent. \^Blue Book, 

 " Lead Compounds in Pottery," 1899, page 32]. Again in 

 the lecture entitled " Pottery and Plumbism," delivered at 

 the Royal Institution, on May 4th, 1900, Dr. Thorpe 

 gave other instances to the same effect, which are in- 

 corporated in the accompanying table : — 



