442 PROCEEDINGS OF THE AMERICAN ACADEMY 



are adequate to the purpose, and that the addition of sodic acetate in 

 reasonable amounts does not sensibly affect conditions. It appears, 

 further, that the addition of a very small quantity of titanium in solu- 

 tion to the clear boiliuij solution of alumina in acetic acid occasions 

 at once a perceptible precipitation. Thus, 0.0005 grm, of titanic 

 oxide in solution produced a distinct and appreciable opalescence in 

 500 cni.^ of liquid containing 10 grm. of alum, 15 grm. of sodic 

 acetate (about twice the amount necessary to convert the sulphate of 

 alumina to the acetate), and seven per cent by volume of absolute 

 acetic acid. 



In respect to holding up alumina, formic acid acts like acetic acid, 

 but more potently. 



In the following experiments to test the method quantitatively, two 

 solutions of titanium were employed; — in (40) and (41), the solution 

 the value of which was fixed by (15) to (18) ; in (42) to (46), the 

 solution whose standard was set by (24) to (27). To the cold solu- 

 tion of titanium containing a little free sulphuric acid together with 

 some alkaline sulphate were added 5 grm. of alum (approximately 

 0.5 grm. of alumina), 20 grm. of sodic acetate, which was always more 

 than enough to effect the entire conversion of the aluminic and titanic 

 sulphates to acetates, acetic acid to such amount that in experiments 

 (42), (43), (44) there should be in the solution seven per cent by 

 volume of absolute acid, and in the remaining experiments ten and a 

 half per cent by volume, and water to make the entire volume 250 cm.' 

 in (40) and (41), and 400 cm.'' in the rest. The clear solutions ob- 

 tained in this manner were raised quickly to boiling, kept at that point 

 for a minute, and removed from over the burner so that the precipi- 

 tate might settle, — as it does almost immediately. The supernatant 

 liquid was decanted upon a filter sufficiently porous to permit very 

 rapid filtration,* and the precipitate added immediately thereafter, and 

 washed with 7% acetic acid followed finally by hot water. The washed 

 precipitate was dried, ignited, and weighed. The precipitate once 

 upon the filter and drained becomes more compact and easily washed, 

 and strong ignition of fifteen or twenty minutes over a good Bunscn 

 burner, after the paper is thoroughly ashed, reduces it to a weight 

 which neither the blast-lamp nor ignition in an atmosphere of ammonic 

 carbonate changes. 



• The paper No. 589 of Schleicher and Schiill is excellent for the purpose. 



