THE RARE EARTHS.—MAGEE. lb-ab-< 
differ from all other elements in their action toward Oxalice acid. All 
oxalates are more or less soluble in acids; but outside the rare earths, 
the solubility is perfect. Calcium oxalate is considered an insoluble 
precipitate, but the reaction must be alkaline, the least trace of mineral 
acid setting up solution, the presence of oxalic acid prevents the precipi- 
tation of alumina, etc., but here we have a group which precipitates at 
once to oxalic acid or to a soluble oxalate in an acid solution, and if only 
faintly acid, say 1 or 2 per cent, the cxalates separate out completely, in 
fact a mere trace is soluble in a 5 per cent acid. Thus we can separate 
them easily as a group. If we render the supernatant liquid more and 
more acid, we can gradually get out portions of which the member first 
removed will differ considerably from that last removed, but probably 
not in a lifetime would one get one member absolutely free from every 
other member. Therein lies the difficulty, and so it is with every reagent 
to some degree. Some reagents shorten the work, and a number of 
persons working together, by being able to do more work get more rapid 
results, but the field is one of great difficulty. 
There are other troubles, however, in the path of the investigator in 
these ficlds. All who have worked practical chemistry are aware that 
there are qualitative tests by means of which we can detect the presence 
or prove the absence of any particular metal or acid. Ammonia acts 
towards a solution of a copper salt as it acts towards nothing else. HCI. 
gives a white precipitate to silver as well as to lead and mercurous salts, 
but the chloride of lead is soluble in hot water and can be washed out, 
that of silver dissolves in ammonia and can in turn be removed while at 
the same time the mercurous chloride turns black but remains insoluble 
owing to the formation of a compound with the ammonia so that it is 
easily determined whether neither one, two or three, or which one is 
present. This makes the work of Mosander the more remarkable, as in 
his time there was nothing to enable him to suspect the different rare 
earths except abstract reasoning from slight color changes. 
In 1858, however, Gladstone, the London chemist, noted on examin- 
ing the light, which had passed through a solution of Didymium salt, with 
a spectroscope, that in certain parts of the spectrum there were dark color 
bands although the solution might be perfectly colorless. These have 
been proved to be due to the absorption of some of the light while 
passing through the solution. This fact of absorption is not of itself 
very remarkable. All colored solutions absorb more or less light, KMnO, 
Proc. & TRANS. N. S. INsT. Scr, VOL. X. PRroc.—G. 
