Browning and Drushel — Separation of Magnesium. 293 



Art. XXVIII. — On the Arsenate Process for the Separation 

 of Magnesium and the Alkalies / by Philip E. Browning 

 and ~W. A. Drushel. 



[Contributions from the Kent Chemical Laboratory of Yale University — civ.] 



Among the methods which have been employed for the 

 separation of magnesium from the alkalies the following are 

 perhaps in most general use : 



The barium hydroxide method, whereby the magnesium is 

 precipitated as the hydroxide by barium hydroxide. 



The mercuric oxide method, whereby the magnesia is pre- 

 cipitated by freshly prepared mercuric oxide acting upon the 

 chlorides. 



The ammonium carbonate method,* whereby the magnesium 

 is precipitated as the double carbonate of magnesium and 

 ammonium by a large excess of ammonium carbonate. 



The amyl alcohol method, f whereby the magnesium chloride 

 is dissolved in boiling amyl alcohol and the chlorides of sodium 

 and potassium, not lithium, remain undissolved. 



None of these methods, when employed with a view to the 

 subsequent estimation of the alkalies, is free from objectionable 

 features, such as difficulties of filtration, numerous transfers of 

 filtrates, introduction of large amounts of reagents difficult of 

 removal, and incomplete separation of the entire alkali group. 



The work to be described is an effort to avoid some of the 

 objections mentioned, by the precipitation of magnesium as 

 the magnesium ammonium arsenate and the removal of the 

 arsenate from the filtrate by reduction and volatilization of the 

 arsenic salt. C. v. Hauer^: suggested this general procedure 

 and it has found other mention in the literature.§ The 

 removal of the excess of arsenic was accomplished by ignition 

 of the residue, obtained after evaporating the filtrate from the 

 ammonium magnesium arsenate, with ammonium chloride. 

 The method, however, has been criticized as inaccurate for the 

 estimation of magnesium, and tedious. Recent work upon the 

 precipitation of magnesium ammonium arsenate and upon the 

 volatilization of arsenic compounds, suggested the possibility 

 of obviating the difficulties which have kept this method from 

 general use. 



It is possible, with careful manipulation, to remove the 

 arsenic by precipitating with hydrogen sulphide, but this pro- 

 cedure required an additional filtration and several transfers of 



* Wulfing, Ber. xxxii, 2214. f Eiggs, this Journal [3], xliv, 103. 



|Jahrb. der'k. k. geolog. Eeichanstalt, iv, 863. 

 §Fresenius-Cohn, Quant. Anal., 6th edition, vol. i, 613. 



Am. Jour. Sci. — Fourth Series, Vol. XXIII, No. 136.— April, 1907. 

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