18 W. R. Nichols on the Chromites of Magnesium. 
boiling dilute chlorhydric acid, the solution thoroughly cooled, 
and then mixed with an excess of a cold aqueous solution of 
caustic soda. The precipitate produced by the soda was filtered 
as rapidly as possible, washed somewhat with water, dried, 
ignited and weighed, while the filtrate was boiled to precipitate 
any chromium which had dissolved. The hydrate of chromium 
thrown down by boiling was ee on a filter, was washed, 
dried, ignited and weighed by 
I, 25098 grm. erties ani and 0°5240 erm. of Epsom 
salt were taken, so that the mixture contained 1:19 equivalent 
of Cr,O, and 1 equivalent of MgO. No magnesium could be 
detected in the filtrate from the precipitate, produced by am- 
monia in this mixture. The ammonia precipitate dissolved in 
chlorhydric acid, and treated with caustic soda in excess, gave 
= only 00103 grm. of Cr,O, to the soda, while 0°3753 grm. 
of Cr,O, went down again “with the magnesium 
An analysis of the ignited soda precipitate gave the follow- 
ing results 
Theory 
Taken. Found. (MgO, Cr.0,). 
a) Mgo 0-0847 00831 18°13 20°73 
) Cr,0, 0°3843 08753 81°87 79°27 
0-4690 0-4584 100-00 100-00 
II. 2:4979 grm. of chrome alum and 0°6150 grm. of Epsom 
salt were taken, so that the mixture contained 1 equivalent of 
used as the precipitant in this instance, and 0-0105 grm. of 
MgO was found in the filtrate from it. ‘When the precipitate 
was dissolved in chlorhydric acid and treated ace soda lye, 
00181 erm. of Cr,O,, went into solution in the so 
Ill. 2:469 grm. of chrome alum and 0-302 of Epsom 
alt. were taken, so that the mixture contained 2-02 equivalents 
of chromic oxyd for 1 equivalent of magnesia. No magnesium 
00 gen detected j in the filtrate from the ammonia precipitate. 
, ‘ of Cr,O, was held dissolved by the soda, and 
3893 gr, of Or, ). ‘was thrown down again with the mag- 
the ° precipitate, —~ solution in chlorhydric acid, 
was as treated = raptors in ex: 
1 Seperate Theory 
Taken. — _ Found. (MgO, 2Cr,0z). 
qu) » 3 00488 = 00492 ~—s: 12°66 11°56 
2Cr,0, 0'3780 083938734 88-44 
04268 0°3885 100-00 —_ 100-00 
isola precipitate gave the follow- 
eee at 
