Matthew Steel 



179 



heated for 30 minutes to expel the SOo, the precipitate is allowed to 

 settle, filtered and washed once by decantation. The precipitate is 

 redissolved in 2 to 2.5 cc. of conc. hydrochloric acid, diluted to about 

 300 cc. with water, and the aluminum reprecipitated as described above. 

 The precipitate is filtered and washed several times with hot water to 

 remove Chlorides, and ignited in a transparent silica crucible in a Meker 

 furnace to constant weight. 



In the following experiments the same relative amounts of the 

 Standard iron sei. that were used in the other experiments were ad- 

 mixed with the alum sei. to keep the conditions identical. In some 

 of the experiments there were added 50 cc. of the following Standard 

 "blank" sol. : 25 gm. of sodium phosphate, 15 gm. of potassium 

 Chlorid, 11 gm. of calcium chlorid, and 11 gm. of magnesium chlorid 

 mixed with 800 cc. of dist. water and just enough HCl to effect sol. ; 

 then made up to i 1. It was assumed that a mixture of sodium alum, 

 ferric chlorid, and the ingredients of the above Standard "blank" 



TABLE 4 



Data pertaining to the estimation of aluminum in a Standard alum sol. by the 



Schmidt and Hoagland tnethod 



