Thorpe and Simmonds, Lead Fritts. 



under closely similar conditions of fineness to that shown 

 by the last three, yield to acids a relatively small propor- 

 tion only of lead. These classes are sharply distinguished 

 by differences of chemical composition, and it is this latter 

 circumstance which is the primary factor determining the 

 solubility. The effect of fineness is a matter apart from 

 this, and altogether subordinate to it. 



Action not that of a solvent on a single substance. — It is 

 tacitly assumed by the writers in question that the process 

 of solution involved is one in which a single substance, 

 one chemical individual, is attacked by a solvent acting at 

 the surface only of the particles [loc. cit., pp. 9, 10). 



If this were so, then, after a first treatment of a fritt 

 with dilute acid, if the solvent be removed and the residue 

 again treated with a fre.sh quantity of the solvent, the 

 amount of lead dissolved should be practically the same as 

 at first. 



Experiment shows that this is not the case. The 

 quantity of lead extracted on the second treatment is only 

 a fraction of that first yielded : — 



