Gooch and Austin — Magnesium Phosphate, etc. 187 



Aet. XIX. — The Constitution of the Ammonium Magnesium 

 Phosphate of Analysis / by F. A. Gooch and Martha 

 Austin. 



[Contributions from the Kent Chemical Laboratory of Vale University — LXXIX.] 



In a recent paper from this laboratory* it has been shown 

 that the presence of ammonium chloride or other ammonium 

 salt is necessary in the precipitation of manganese as the ammo- 

 nium manganese phosphate by microcosmic salt in order that 

 the precipitate may have the ideal constitution represented 

 by the symbol NH 4 MnP0 4 . 



It was also shown that the solvent effect of the ammonium 

 chloride upon the precipitated ammonium manganese phos- 

 phate is not marked when an excess of the precipitant is 

 present in solution. 



The relations disclosed in this paper suggest that the chem- 

 ical constitution of the precipitate rather than mechanical con- 

 tamination and varying solubility — the explanations generally 

 accepted, and, indeed, advocated by one of us in a former 

 paperf — may be responsible for observed variations in the 

 weight of the residue derived by the ignition of the similar 

 salt of magnesium, the ammonium magnesium phosphate, pre- 

 cipitated by an excess of a soluble phosphate from the solution 

 of a magnesium salt, or from the solution of a soluble phos- 

 phate by an excess of a magnesium salt. 



Precipitation by Excess of the Soluble Phosphate. 

 The precipitation of the magnesium salt by an excess of the 

 soluble phosphate was first studied. For this work a solution 

 of pure magnesium nitrate was prepared by dissolving the 

 pure magnesium oxide of commerce in a slight excess of pure 

 hydrochloric acid and boiling with more magnesium oxide. 

 After filtering off the excess of magnesium oxide and any trace 

 of iron or members of the higher groups, the solution was pre- 

 cipitated by ammonium carbonate, the precipitate was washed 

 by repeated boilings and filtrations until silver nitrate gave no 

 precipitate in the solution acidified with nitric acid. This pre- 

 cipitated carbonate was nearly dissolved in nitric acid and the 

 solution was boiled with an excess of the carbonate (for the 

 purpose of removing traces of barium, strontium, and calcium) 

 filtered, and diluted to definite volume. The evaporation of a 

 definite volume of the solution and strong ignition of the resi- 

 due would be a most natural method of establishing a standard 



* This Journal, vi, 233. 

 f Am. Chem. Jour., i, 391. 



Am. Jour. Sol— Fourth Series, Yol. VII, No. 39 — March, 1899. 

 13 



