12 Thorpe and Simmonds, Lead Fritts. 



What is maintained is, that within the limits of fine- 

 ness occurring in actual practice the variation of solubility 

 is too small to be of serious moment. This may be shown 

 by reference to the following experiments, described on 

 p. 9 of the Parliamentary Paper (Cd 527) " On the Use of 

 Lead in the Manufacture of Pottery." 



Equal weights of six specimens of fritt, having solu- 

 bilities ranging from ri to 3*2 per cent., were ground 

 together for 24 hours in a hand-mill. The powder was 

 then of fully an average working degree of fineness, and 

 its solubility was 2*8 per cent. After being reduced to 

 what must be regarded as a somewhat extreme state of 

 sub-division, by further grinding for 12 hours, the solu- 

 bility was 3'6 per cent. 



Now the percentage of lead oxide contained in the 

 mixed fritts was 46 "O. If, therefore, the mixture in the 

 first state of division were used to supply the lead in a 

 glaze containing 15 per cent, of lead oxide, the solubility 

 of this glaze would be O'QI per cent. If it were used in 

 the second or extremely fine state of sub-division, the solu- 

 bility would be v\y per cent. The difference is by no 

 means an inappreciable one, but it is certainly not a 

 matter of importance. Both figures, it will be seen, are 

 much below the suggested limit of 2 per cent. 



Summary. — It has been shown : — 



(i) That a fallacy underlies Messrs. Jackson and Rich's 

 conclusions, inasmuch as a fritt does not, as they assume, 

 necessarily consist of a single chemical compound. 



(2) That the hypothesis of a protective la)cr of silica, 

 essential for the authors' explanation of the observed 

 behaviour of fritts, is not in accordance with certain 

 easily-demonstrated facts. 



(3) That some of the authors' experiments are in- 



