■586 REPORT— 1886. 



one of one base and one of the other ; and the two molecules thus intimately- 

 associated might tend to remain together, whether as precipitate or as filtrate. On 

 the whole, I prefer nitric acid, as having little tendency to form double salts, and 

 being easily got rid of. 



It is occasionally necessary to completely precipitate the whole contents of the 

 bottles with ammonium oxalate, and after ignition to redlssolve the earths in 

 acid and proceed as before. If this precaution is not adopted the accumulation of 

 ammonium nitrate in the solution dissolves an appreciable amount of the earths. 



In the ordinary operations of separating distinct entities, such as the known 

 gadolinite or samarskite earths, it is not difficult, as I have already pointed out, 

 to find different chemical processes, which may be successively employed. When, 

 however, the separations attempted are those of the constituents of yttrium, the 

 simple straightforward fractionation, continued steadily month after month and 

 year after year, is the only plan I know of. 



The operation may be somewhat hastened by removing from the main series 

 certain bottles in which one particular constituent is concentrated and sub- 

 fractioning these by themselves. Also to avoid the spreading out sideways to too 

 great an extent after a certain distance has been proceeded from the centre, say 

 to bottles — 20 and + 20 : the earths are allowed to accumulate in the last bottle 

 at each end. They will after a time be in sufficient amount to subfractionate on 

 their own account, and, being at the end of the series, they ofler a good chance of 

 getting the extreme constituents pretty pure. 



It will be seen from the above description that there is little hope of success 

 in fractionation unless the supply of crude earths is very large. In my laboratory 

 I have, either worked up or ready for working, over 50 kilos, of samarskite con- 

 taining about 10 per cent, of yttria, and about 20 kilos, of gadoHuite containing 

 48 per cent, of yttria, besides a considerable quantity of other rare yttria minerals, 

 giving a total yield of about 15 kilos, of yttria. 



4. On the Fractionation of Yttria.^ 

 By William Crookes, F.B.S., V.P.C.S. 



Having already explained the methods of chemical fractionation, it is necessary 

 now to describe some of the results yielded by an extended perseverance in these 

 operations. 



I must, in the first place, explain that my work has been confined to a limited 

 and very rare group of bodies — the eartliy bases contained in such minerals as 

 samarskite, gadolinite, &c. These have been i-epeatedly put through the fractiona- 

 tion mill by other chemists, but the results have been most xmsatisfactory and 

 contradictory, no sufficiently good test being known whereby the singleness of any 

 earth got out by fractionation could be decided, except the somewhat untrust- 

 worthy one of the atomic weight. I say untrusticoi-thy because it is now known 

 that fi-actionation, unless it is pushed far beyond the point to which some Conti- 

 nental chemists have even carried it, is quite as liable to give mixtures which 

 refuse to split up under further treatment of the same kind, as it is to yield a 

 chemically simple body. 



It is well known that a limited group of these rare earths, when phosphoresced 

 in vacuo, yield discontinuous spectra. The method adopted to bring out the spectra 

 is to treat the substance under examination with strong sulphmlc acid, drive off 

 ■excess of acid by heat, and finally to raise the temperature to dull redness. It is 

 then put into a radiant-matter tube, of the form shown in fig. 1, and the induc- 

 tion spark is passed through it after the exhaustion has been pushed to the required 

 degree. The phosphorescence occurs beneath the negative pole. Bodies like yttrium 

 sulphate, &c., under the stimulus phosphoresce, emitting light whose waves tend 

 to collect round definite centres of length. The phosphorescent light which the 

 discharge evokes is best seen in a spectroscope of low dispersion, and with not too 



' The original paper was published in extenso in the Chemical jVe/vs for September 

 :2i, 1886. 



