EIvISHA MiTCHELIv SCIENTIFIC SOCIETY. 49 



until the wash water amounted to about twice as much 

 as the orig-inal solution. This amount of washing- was 

 arbitrarily^ chosen, as it was found that if it was consid- 

 erably less the results ran hig-h, showing- imperfect 

 washing-, due to the presence of sulphite, no doubt. The 

 presence of free acid (one per cent, and less) interfered 

 considerable^ preventing- complete precipitation (39 and 

 4-0 -vi'd. below). Moreover the precipitate was finely 

 divided and ran throug-h very close filter paper (S and 

 S, No. 590) along- with much free sulphur. The 

 precipitation was made in the cold as well, but in that 

 case, it was found necessary to let the solution remain 

 covered for at least twent^^-four hours with occasional 

 stirring-. The larg-er portion of the flocculent precipi- 

 tate collected well at the bottom of the beaker, but a 

 small portion clung- persistently to the stirring rod and 

 sides of the beaker, refusing- to come off, even on the 

 most vig-orous rubbing- with a "policeman." 



This reag-ent will not serve as a precipitant for the 

 zirconium sulphate solution, since the precipitation was 

 found to be incomplete on addition of as much as twen- 

 ty per cent, of solid sodium thiosulphite to a thoroug-h- 

 ly neutralized solution. Preliminary experiments were 

 made with more or less free sulphuric acid present and 

 varying- amounts of the thiosulphite (two to twenty per 

 cent.) in solution and solid form, hot and cold. 



These determinations were made : 



Ninnbers. Found. . Used. 



33 0.1102 1 



34 0.1101 y 0.1104 



35 0.1106 J 



36 0.1645 0.1635 



37 0.1079 0.1104 



38 0.1641 0.1635 



