THE RARE EARTHS. MAGEE. Ixix 



differ from all other elements in their action toward Oxalic acid. All 

 oxalites 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 tne 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 fields. 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. HC1. 

 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, KMn0 4 

 PROG, & TRANS. N. 3. INST. Soi., VOL. X. PROC.-G. 



