12 Jackson and Rich, Solubility of Lead Glasses. 

 Action of I per cent. NaOH Solution. 



a. I gr. frilt + HCl 2-2 mg. PbO extrd. 



/'. Residuefionirt + 1% NaOH solut'n. 1-3 mg. SiOo „ 

 c. „ „ ^ + HC1 2-1 mg. PbO „ 



d. I gram fresh fritt + 1% NaOH sol'n. No SiO, „ 



.'. layer of silica = i"3 mg. 



e. Residue from ^+HC1 3'3 mg. PbO „ 



Seeing that even i per cent, solution caustic soda 

 caused an increase in the solubility of the lead oxide in a 

 fresh fritt, we considered the method to be unsatisfactory 

 and it was abandoned in favour of 



(B) MECHANICAL METHOD. 



A fritt which had been shaken with hydrochloric acid 

 until no more lead oxide was dissolved, the amount 

 obtained being 7 per cent., was lightly rubbed in an agate 

 mortar and once more shaken with acid. Lead oxide 

 was found to have passed into solution. This led us to 

 examine the matter systematically. 



Five grams of a glaze containing about 18 per cent, 

 lead oxide were placed in an Alsing cylinder with 2,000 cc. 

 dilute (0'25 per cent.) hydrochloric acid and a quantity of 

 clean flint pebbles. The c}'linder was rotated for various 

 lengths of time, after the expiration of which the dissolved 

 lead oxide in 50 cc. was determined. 



It was thought that, by the friction of the contents of 

 the cylinder, the insoluble siliceous layer would be rubbed 

 off continuously as it was produced, and so the action of 

 the acid would not be interfered with, and the amount of 

 lead oxide dissolved should be found to continually 



