43G PROCEEDINGS OP THE AMERICAN ACADEMY 



ditious more exact, method of separation by boiling to the convenient 

 but indubitably inaccurate process of parting by the use of sodic 

 hydrate. Knop employs both the dry and the wet method, — the 

 fusion of the oxides in sodic hydrate, and the treatment of the salts 

 in solution with sodic hydrate in excess ; but both had long before 

 been generally discarded, and the single experiment of acidulating 

 the alkaline filtrate from a precipitate obtained by the treatment of 

 a pure titanium salt according to either mode, and then making alka- 

 line with ammonia, is enough to prove their worthlessness. 



In an endeavor to secure a better means of separating titanium 

 from aluminum I have followed two lines of experimentation ; — the 

 one based upon the observation that, under properly controlled con- 

 ditions, titanium is completely precipitated and alumina held in solu- 

 tion when an alkaline orthophosphate, strongly acidified with formic 

 acid, is added to the solution of salts of these elements ; the other, 

 upon the solubility of alumina and the insolubility of titanic hydrate 

 in sufficiently strong boiling solutions of acetic acid. Two prepara- 

 tions of titanium were used as test material in the course of the work ; 

 — the solution of the fusion in sodic bisulphate of the hydrate precipi- 

 tated by ammonia from the fluoride of titanium and potassium itself 

 made from rutile and carefully purified by recrystallization ; and the 

 solution obtained by treating the carefully prepared double fluoride 

 with sulphuric aciJ, evaporating to dryness, redissolving in sulphuric 

 acid and diluting with water. The second mode of preparation is the 

 better, because the amount of alkaline sulijhate present in the test so- 

 lution is much smaller. At first, the strength of the solution was fixed 

 by precipitating weighed amounts by ammonia, carefully washing, 

 igniting and weighing the precipitate ; but in the course of the work 

 it became plain that the precipitation by means of ammonic acetate, 

 or by ammonia with the subsequent addition of acetic acid in distinct 

 excess, yielded more precise results. On this account, therefore, the 

 determinations of the standard of the solutions employed in tlie later 

 work were made by the acetic acid process, and the determinations by 

 ammonia were corrected to correspond. In some of the experiments 

 bearing upon this point, the results of which are given in the figures 

 below, precipitations by ammonia were made in the cold and the 

 liquid then heated to boiling ; in those in which acetic acid was used 

 just in excess, this reagent succeeded the ammonia at once, and the 

 boiling followed ; when precipitation was effected in presence of large 

 amounts of acetic or formic acid, the acid was added in the amount 

 intended, sodic acetate in quantity more than that necessary to decom- 



