eh 
ee: 
W. R. Nichols on the Chromites of Magnesium. 17 
taining any considerable proportion of sesquioxyd of chromium 
as well as magnesium, the greater part or the whole of the 
latter will be thrown down, together with the chromium, on 
the addition of ammonia, even when the solution is highly 
charged with chlorid of ammonium. 
Sulphid of ammonium, also, like ammonia, throws down from 
mixed solutions of chromium and magnesium a compound 
precipitate well-nigh insoluble in water and saline solutions. 
If no serious difficulty has been met with hitherto in detecting 
magnesium in presence of chromium by the ordinary method 
of qualitative analysis, it is doubtless owing to the fact that, 
in pursuing this method, some of the magnesium thrown down 
in combination with chromium will be encountered when the 
precipitate produced by sulphid of ammonium comes to be ex- 
amined in regular course for (barium, strontium, calcium and) 
magnesium, which may have fallen down in combination with 
phosphoric, boracic, oxalic, or silicic acid, or in the form of 
fluorids; and this, even if nothing but chromium and magne- 
As thrown down either by ammonia or by sulphid of am- 
monium, the compound precipitate of chromium and magne- 
tween the maenesia and the chromic oxyd, I have devoted 
} J 
particular attention to the study of the precipitates thus pro- 
Equivalent quantities of chrome alum and E som salt were 
weighed out and dissolved in water with addition of chlorid of 
or 
separately, the chlorid of ammonium being added to the solu- 
tion of sulphate of magnesium before mixing the two solutions. 
in each case to determine the amount of nesium in the 
‘filtrate by precipitation with phosphate of sodium. Negative 
results were obtained for the most part in these trials, as will 
be seen below. 3 ee 
The precipitate thrown down by ammonia was dissolved in 
Am. Jour. Sci.—Secoxp Senres, Vow. XLVI, No. 139.—Jay., 1869. 
2 ah 3 s 
