590 REPORT— 1886. 



of the otlier constituents, G/3 is plentiful and the red is good. Yttrium from 

 fluocerite is very similar to that from monazite, hut Ga is weaker. Yttrium from 

 hielmite is very rich in GS, has a fair quantity of Ga and G/3, less of Gy, no S5, 

 and only a very faint trace of Grj. Yttrium from euxeuite is almost identical 

 ■with that from hielmite. Yttrium from cerite contains most G( and G8, less Ga 

 and G^, only a trace of Grj, and a fair proportion of S8. 



Referring to the diagram it is seen that Ya (gadolinium) is composed of the 

 following hand-foi-ming bodies: — G/3, SS, G^, togetlier with a little samariiun. 

 Calling the samarium an impurity, it is thus seen that gadolinium is composed of 

 at least three simpler bodies. 



You have probably anticipated in your minds a question which is likely to 

 occur at this point of the enquiry. If such results have been obtained by sub- 

 mitting yttrium to this novel method of analysis, what will be the result of 

 fractionating some other reputed element ? 



Yttrium, as I have explained, is an exceedingly stable molecular group, capable 

 of acting as an element, just as calcium, for instance, acts as an element : to split 

 up yttrium requires not only enormous time and material, but the existence of a 

 test by means of which the constituents of yttrium are capable of recognition. 

 Had we tests as delicate for the constituent molecular groups of calcium, this also 

 might be resolved into simpler groupings. It is one thing, however, to find out 

 means of separating bodies which we know to be distinct and have colour or 

 spectrum reactions to guide at every step ; it is quite another thing to separate 

 colourless bodies which are almost identical both in chemical reaction and atomic 

 weight, especially if we have no suspicion that the body we are dealing with is a 

 mixture. 



One of the chief difficulties in the successful carrying out of an investigation in 

 radiant-matter spectroscopy is the extraordinary delicacy of the test. This extreme 

 sensitiveness is a drawback rather than a help. To the inexperienced eye one part 

 of yttrium in ten thousand gives as good an indication as one part in ten, and by 

 far the gi'eater part of the chemical work undertaken in my hunt for spectrum- 

 forming elements was performed upon material which later knowledge shows did 

 not contain sufficient to respond to any known chemical test. It is as if the 

 element sodium were to occur in ponderable quantity only in a few rare minerals 

 seldom seen out of the collector's cabinet. With only the yellow line to guide, 

 and seeing the brilliancy with which an imponderable trace of sodium in a mineral 

 declares its presence in the spectrum, I venture to think that a chemist would have 

 about as stiff a hunt before he caught his yellow line as I have had to bring my 

 orange and citron bands to earth. 



Chemistry, except in a few instances, such as water-analysis and the detection 

 of poisons, where necessity has stimulated minute research, takes little account of 

 ' traces,' and when an analysis adds up to 99'999, the odd O'OOl per cent, is conve- 

 niently put down to ' impurities,' ' loss,' or 'errors of analysis.' When, however, 

 the 99-999 per cent, constitutes the impurity and this exiguous 0-001 is the precious 

 material to be extracted, and when, moreover, its chemistry is absolutely unknown, 

 the difficulties of the problem become enormously enhanced. Insolubility as 

 ordinarily understood is a fiction, and separation by precipitauts is nearly impos- 

 sible. A new chemistry has to be slowly built up, taking for data uncertain and 

 deceptive indications, marred by the interfering power of mass in withdrawing 

 soluble salts from a solution, and the solubiUty of nearly all precipitates when 

 present in traces in water or in ammoniacal salts. '\\'hat is here meant by ' traces ' 

 will be better understood if I give an instance. After fifteen months' work I 

 obtained the earth yttria in a state which most chemists would call absolutely 

 pure, for it contained not more than one part of impurity (samaria) in two hundred 

 and fifty thousand parts of yttria. But this one part in a quarter of a million pro- 

 foundly altered the character of yttria from a radiant-matter-spectroscopic point of 

 view, and the persistence of this very minute quantity of interfering impurity 

 entailed another ten months' extra labour to eliminate these final ' traces ' and to 

 ascertain the real reaction of the earth called yttria. 



