4 Jackson and Rich, Solubility of Lead Glasses. 



and was then found to give up an amount of lead oxide 

 equal to 075 per cent, of its dry weight when shaken for 

 one hour with lOOO times its weight of a 0-25 per cent, 

 solution of HCl ; on the other hand, when ground in a 

 mill, as before described, the solubilitj' was found to be 

 7-02 per cent., that is the solubility was increased nearly 

 ten times. 



Another fritt, when exceedingly finely ground by 

 hand, showed a solubility of 3 per cent. ; while when mill- 

 ground this was increased to 4*4 per cent. 



We then proceeded to a systematic examination of 

 the question, using Schone's elutriation apparatus (see 

 Fig. i). The method adopted was the following: — The 

 former of the two fritts before mentioned was well ground 

 in an agate mortar and the lighter particles washed 

 out with water into the apparatus. This operation was 

 continually repeated on the coarse residue in the mortar 

 until all was removed. When water flows steadily through 

 the apparatus, as the water rises in the conical part, its 

 velocity diminishes regularly until the cylindrical portion 

 is reached, when it is a minimum. All particles which 

 have been carried into the cylindrical region will, by the 

 same current of water, be eventually carried out of the 

 apparatus. Hence, by means of definite successive increases 

 in the velocity of the water in this part of the apparatus, 

 it is possible to separate a powdered material into a 

 number of fractions of constantly increasing coarseness. 

 The velocity of the water current is determined by the 

 height of the water in the piezometer, each instrument 

 having been calibrated. 



The material was thus separated into various fractions 

 by subjecting it to the action of currents of water of 

 definite velocities, these being regulated by the height of 

 the water column in the piezometer. The whole of the 



