Manchester Memoirs, Vol. xlv. (1900), No. 3. I 5 



that we were dealing with 5 grms. only of soHd in 2,000 of 

 Hquid, that any great grinding efficiency could be obtained, 

 and hence the very large increase in solubility observed 

 could not be due entirely to increased fineness. On the 

 other hand any insoluble pellicle formed would be soft 

 and easily removed even in a suspension of such small 

 solid contents. We intend to pursue this point further, 

 but the results of our experiments tend to show that the 

 apparent insolubility of a fritt after extraction with 

 hydrochloric acid is not due to its actual insolubility as a 

 whole, but rather to the formation of a protective insoluble 

 layer of silica on the surface of the particles. 



Our thanks are due to the Technical Instruction 

 Committee of the Staffordshire County Council in whose 

 Pottery Laboratory the work has been conducted. 



Victoria Institute, Tunstall, Staffs. 



