438 PROCEEDINGS OP THE AMERICAN ACADEMY 



It will be noticed in the examination of these figures that parallel 

 determinations usually agree very closely. The amounts of titanic 

 oxide indicated by those experiments in which the precipitation was 

 made by ammonia, are much in excess of those in whicli acetic acid 

 was added subsequently. Thus the difference between (1), (2) and 

 (3), (4) amounts to more than three per cent of the total amount of 

 the former; that between (5), (6) and (7), (8), to a little less than 

 two per cent; that between (9), (10) and (11), (12), to about two 

 and a half per cent; and a correction of more than two per cent must 

 be applied to (13), (14) to bring them to correspondence with (15), 

 (IG), (17), (18). The diiference between (21), (22), (23) and (24), 

 (25), (2G), (27) is about one per cent, and the smallness of tliis fig- 

 ure in comparison with the differences previously noted is apparently 

 explicable by the fact that the solution of titanium employed in the last 

 determinations was prepared by the second of the methods mentioned 

 above, and carries a smaller amount of alkaline sulphate. The tendency 

 of titanic hydrate to include the sulphates of the alkalies is not strange 

 in view of the well-known conduct of aliiniinic hydrate under similar 

 circumstances, but the amount thus held is rather surprising. The 

 experiments in which different proportions of free acid were intro- 

 duced go to show, very strikingly, that, if acetic acid exerts any solvent 

 action whatever upon the precipitate thrown down by boiling the 

 acetate, that action is very slight. Thus, between the mean of (24), 

 (25) and that of (26), (27), — the one set precipitated by ammonia 

 and treated before boiling with just a distinct excess of acetic acid, 

 the other pair thrown out of a large volume, 700 cm.^, one half of 

 which was acid of 35% strength, by boiling, — we find a difference of 

 but 0.0007 grm., and between the mean of (15), (10) and that of 

 (17), (18), the difference (magnified five times by reference to 50 grm. 

 portions) is 0.0010 grm. In (25), too, we have an experiment in which 

 the weighed precipitate was fused in sodic carbonate, dissolved, and 

 again precipitated as before and wciglicfl, the two weights differing 

 by 0.0003 grm. Moreover, the filtrates from the precipitates thrown 

 out in presence of an excess of acetic acid, when neutralized with am- 

 monia, fiiiled invariably to show the smallest precipitate, and in direct 

 experiments upon the sensitiveness of the reaction it was found that 

 on the addition of 0.0005 grm. of titanic oxide in solution to 100 cm.' 

 of 35% acetic acid carrying a little sodic acetate a distinct precipi- 

 tate appeared almost immediately on boiling. It is plain, therefore, 

 that so far as concerns the purpose in hand the insolubility of the 

 titanium precipitate in acetic acid may be taken as absolute. The 



