446 PROCEEDINGS OP THE AMERICAN ACADEMY 



permanganate. The oxidation of tartaric acid by potassic permanga- 

 nate does not, as is well known, yield carbonic acid and water alone, 

 but gives rise also to a considerable quantity of formic acid as an in- 

 termediate product. When the permanganate begins to act upon the 

 formic acid, the oxidation, going more slowly, results in the deposition 

 of a brown manganic hydrate, which, if any tartaric acid remains in 

 solution, redissolves quite rapidly, and, in presence of formic acid as 

 the only reducing agent, more slowly. When, therefore, manganic 

 hydrate is abundantly precipitated in the boiling solution, and does 

 not perceptibly dissolve, it is quite certain that the conversion of the 

 tartaric acid to formic acid — which is all that is needed in this case — 

 has been accomplished; but for the sake of greater security the addi- 

 tion of permanganate may be continued until its color shows in the 

 solution. It is well, however, to make use in this process of a known 

 amount of tartaric acid, — experience has shown that an amount equal 

 to three times the weight of the oxides to be held in solution is suffi- 

 cient, unless ammonia be used in enormous excess and the -boiling 

 prolonged, — and to employ for its destruction two and a half times 

 its own weight of potassic permanganate, this quantity being more 

 than enough to carry the oxidation to the final products, providing 

 there were no deposition of manganic hydrate. The manganese thus 

 introduced into the solution may be removed by two acetate precipi- 

 tations, which, if alumina is to be separated, must be made at any rate, 

 even if no manganese be present. 



To separate titanium, aluminum, and iron, therefore, I find it most 

 convenient to preci{)itate the iron by passing hydric sulphide into the 

 faintly ammoniacal solution of the oxides in ammonic tartrate, taking 

 care that the solution is still ammoniacal ju.st before filtering; to de- 

 stroy the tartaric acid in the filtrate, after acidifying and boiling off 

 the hydric sulphide by means of potassic permanganate in the manner 

 just described, redissolving residual manganic hydrate by the addition 

 of a little ammonic bisulphite and boiling off the excess of sulphur- 

 ous acid ; and to separate the titanium and aluminum by the acetate 

 process. 



A single point in the analysis of silicates may be worthy of note in 

 this connection. If phosphoric acid be present, as is often the case, 

 the separation of titanium from silica by the action of cold water upon 

 the product of fusion in sodic or potassic bisulphate is liable to uncer- 

 tainty, on account of the formation of the insoluble titanic phosphate 

 which remains partly with the silica and in part clouds the filtrate. 

 The siliceous residue should, therefore, be treated with sulphuric and 



