8 Thorpe and Simmonds, Lead Fritts. 



These results show that in the soluble portion the 

 constituents do not bear the same proportion to one 

 another as obtained in the original fritt. The lime and 

 alkalis are as a rule higher ; the lead oxide and alumina 

 somewhat lower. Hence it would appear that some process 

 of selective solution has occurred, and that the fritt was 

 therefore not originally a single chemical body. 



II. Physical. — If a fritt consisted of only one chemical 

 compound it could not by any process of grinding and 

 levigation be separated into fractions having different 

 densities. But there is experimental evidence to show 

 that such fractions do result when some fritts are ground 

 and elutriated. Thus determinations were made of the 

 specific gravity of three elutriated fractions, a, /3, and y, of 

 the same fritt, the results being : — 



Specific Gravity (-^— 5|ofo 3'683 



» » >. ft 3742 



.. .. 5, 7 3'6o6 



Had the fritt been a single compound the three results 

 should have been the same, within the limits of experi- 

 mental error. 



Thus the facts adduced, both chemical and physical, 

 tend to show that, at least in some kinds of fritt, there is 

 present a certain proportion — which, however, may be but 

 small — of a readily-soluble lead compound in a state of 

 admixture with the bulk of the fritt. 



Explanation of Messrs. Jackson and Ric/is elutriation 

 experiments. — This consideration suggests the explanation 

 of some results obtained by Messrs. Jackson and Rich, 

 and displa}'ed on the table on p. 5 {Joe. cit.). That table 

 purports to show that a fritt "A" has a solubility of i ^ 

 per cent, when in the condition of fineness corresponding 



