Chemistry and Physics. 489 



A remarkable modification of phosphorescence spectroscopy is 

 produced by the previous addition of other earths to the specially 

 phosphorescent earths. Lime is a good example of this. Alone 

 it phosphoresces with a continuous spectrum ; but if mixed with 

 yttria the phosphorescing energy of the lime does not extend 

 over the whole spectrum, but concentrates itself on strengthening 

 the yttria bands ; these bands becoming broader and less well 

 defined as the quantity of the lime increases. The same is true 

 of the samarium spectrum, the addition of lime bringing out its 

 main phosphorescent bands, three in number, red, orange and 

 green, nearly equidistant. On the other hand the presence of 

 lime suppresses the sharp line So\ the most striking feature in the 

 phosphorescent spectrum of samarium sulphate ; while the pres- 

 ence of yttria deadens the other lines, but brings out the line Stf 

 more strongly. The modification induced in the normal spectrum 

 of one earth by the mixture of various quantities of others, when 

 treated as anhydrous sulphates, is strikingly shown in the case of 

 a mixture of samaria with yttria. The presence of even 40 per 

 cent of yttria practically obliterates its spectrum. Stroutia, 

 baryta, glucina, thoria, magnesia, lanthana, alumina and the 

 oxides of zinc, cadmium, lead, bismuth and antimony all give 

 characteristic spectra with samaria. " A recent discovery of 

 some beautiful spectra given by the rare earths when their pure 

 oxides are highly calcined, shows the remarkable changes pro- 

 duced in the spectra of these earths when two or more are ob- 

 served in combination." Alumina is especially active in inducing 

 new spectra when mixed with the rare earths. Within the past 

 twelve months, quite a moderate amount of fractionation has 

 enabled the author to penetrate below the surface of the red glow 

 common to crude alumina and to see traces of a most complicated 

 sharp line spectrum. " By pushing one particular process of 

 fractionation to a considerable extent, I have obtained evidence 

 of a body which is the cause of some of these lines. The new 

 body is probably one of the rare elements or meta-elements 

 closely connected with decipia, for I have reproduced the spec- 

 trum very fairly by adding decipia to alumina. It is not yttria 

 erbia, samaria, didymia, lanthana, holmia, thulia, gadolinia, or 

 ytterbia, since the spectrum of each of these when mixed with 

 alumina while very beautiful, differs entirely from the decipia- 

 alumina spectrum. 



In conclusion, the author considers the question, " What is an 

 element and how shall it be recognized when met?" It must be 

 remembered that a single operation, be it crystallization, precip- 

 itation, fusion, partial solution, etc., can only separate a mixture 

 of several bodies into two parts, just as the addition of a reagent 

 only divides a mixture into two portions a precipitate and a solu- 

 tion ; and these divisions will be effected along different lines 

 according to the reagent employed. Thus by crystallizing didy- 

 mium nitrate (in Auer's way) we divide the components into two 

 parts. By fusing didyminm nitrate we divide its components in 



