Manchester Memoirs, Vol. xlv. (1901), No. 15. 11 



least 5 to 6 per cent., or about one-third of the whole 

 quantity of lead present. Any argument legitimately 

 derived from the behaviour of this glaze is thus an 

 argument against the employment of glazes yielding a 

 solubility-figure of so high a value as 5 or 6 per cent. But 

 this argument has no necessary validity against glazes 

 whose solubilities are less than 2 per cent., since the lead 

 fritts used in the two cases must be of different chemical 

 composition if the glazes have the same lead-content. It 

 is useless to base a contention against the 2 per cent, 

 limit upon the behaviour of a glaze which is obviously 

 outside that limit. 



In this connection it may be pointed out that the chief 

 experiments upon which Messrs. Jackson and Rich rely 

 are made with fritts having somewhat considerable initial 

 solubilities. Thus the fritts A and B on p. 5, and the 

 di-silicate of p. 14, have solubility-figures of 70 (mill- 

 ground), 5'0, and 8'2 respectively. It would have been 

 more to the point if the experiments had been carried out 

 on fritts of low solubility — say i or 2 per cent. Even if 

 it be admitted for a moment that the experiments are 

 satisfactory, they only show that it is possible to select 

 fritts of a certain character which shall behave in the 

 manner indicated. They prove nothing, and they can 

 prove nothing, with respect to the behaviour of fritts 

 having lower solubility, and therefore different chemical 

 composition. 



Effect of grinding of no importance. — Turning again to 

 the practical side of the matter ; it has never been con- 

 tended that fineness of sub-division is absolutely without 

 effect upon the quantity of lead dissolved. It is a mere 

 commonplace to admit that when solvent action occurs, 

 it is exerted more readily upon an impalpable powder 

 than upon the same substance in the form of coarse 

 granules. 



