584 
performed by a thermo-regulator. On the other hand, in 
apparatus heated by coal or coke the temperature continually 
tends to vary, and can only be maintained uniform by constant 
attention on the part of the stoker. 
In very few hot-air chambers did the thermometer with which 
the apparatus was provided afford a trustworthy indication of the 
temperature of the interior; in some instances there was an 
error of as much as 100° F,_ This is due to the thermometer, 
for reasons of safety and accessibility, being placed in the coolest 
part of the chamber, and to the bulb being inclosed for protec- 
tion in a metal tube which screens it from the full access of heat. 
The difficulty may be overcome by using, instead of a thermo- 
meter, a pyrometer actuated by a metal rod extending across the 
interior of the chamber. 
In steam apparatus the three requirements above mentioned 
are all satisfactorily met, and for this reason, as well as on account 
of the greater rapidity and certainty of action of steam, both 
in penetrating badly conductive materials and in destroying 
contagia, steam chambers are, in Dr. Parsons’s opinion, greatly 
preferable to those in which dry heat is employed. 
It is important that the arrangements of the apparatus, the 
method of working, and the mode of conveyance to and fro, 
should be such as to obviate risk of articles which have been 
submitted to disinfection coming into contact with others which 
are infected. 
The latter part of the Report is taken up with descriptions of 
the various forms of apparatus in use for disinfection by heat, 
and accounts of experiments made with a view to test their prac- 
tical efficiency. 
ON THE FRACTIONATION OF YTTRIA? 
AVING already explained the methods of chemical fractiona- 
tion, it may be useful 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 con- 
fined to a limited and very rare group of bodies—the earthy 
bases contained in such minerals as samarskite, gadolinite, &c. 
These have been repeatedly put through the fractionation mill 
by other chemists, but the results have been most unsatisfactory 
and contradictory, no sufficiently good test being known whereby 
the singleness of any earth got out by fractionation could be 
decided, except the somewhat untrustworthy one of the atomic 
weight. I say wntrustworthy, because it is now known that 
fractionation, unless it is pushed far beyond the point to which 
some Continental chemists have even carried it, is quite as liable 
to give atures which refuse to split up under further treatment | 
of the same kind, as it is to yield a chemically simple body. 
This I have fully gone into in my paper ‘‘ On the Methods of 
Chemical Fractionation.” The unsatisfactory nature of frac- 
tionation work may be seen from expressions used, in private 
letters to me, by some of the eminent chemists who have almost 
made this method their own. One writes—‘‘ It is very tiresome 
working with the rare earths, as we never can be sure when we 
have got a definite result. There will never be an end to their 
history. I am very tired of it, and am much inclined to give it 
up.” Another writes—‘‘ Unfortunately I commenced my re- 
searches on the rare earths with too little material, and I have 
not had the courage, at my age, to recommence the work on 
more abundant material. The further I advance in my work 
the more I am convinced that no known method permits of the 
complete separation of these different earths one from the other.” 
A third writes—‘‘ One loses so much material in the separations 
that it appears to me scarcely possible, with the material avail- 
able, to arrive at a successful solution of the question.” I could 
multiply similar quotations, all breathing the same almost 
despairing spirit. 
It would certainly not have been prudent on my part to invite 
a time-honoured comparison, and ‘rush in” where so many 
eminent men “fear to tread,” were it not that good fortune had 
placed in my hands a physical test for these obscure molecular 
groupings which is of the most exquisite sensitiveness. I refer 
to what I have for shortness called the Radiant-Matter test. 
It is well known that a limited group of these rare earths, 
when phosphoresced #7 vacuo, yield discontinuous spectra. The 
method adopted to bring out the spectra is to treat the substance 
under examination with strong sulphuric acid, drive off excess of 
acid by heat, and finally to raise the temperature to dull redness. 
* A Paper read before Section B of the British Association at the Bir- 
m‘ngham meeting, by William Crookes, F.R.S., V-P.C.S 
NATURE 
[Oct. 14, 1886 | 
It is then put into a radiant-matter tube of the form shown in 
Fig. 1, and the induction spark is passed through it after the 
exhaustion has been pushed to the required degree. The phos- 
phorescence occurs beneath the negative pole. As each gaseous 
molecule, carrying its charge of negative electricity with it, 
strikes the earthy sulphate, it has a tendency to part with its 
charge, provided it finds a body ready to take up the electricity ; 
otherwise it retains its charge. Bodies like yttrium sulphate, 
&c., easily take the clectric charge, and 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 narrow a slit. In appearance the bands are 
more analogous to the absorption-bands seen in solutions of 
didymium than to the lines given by spark spectra. Examined 
with a high magnifying power, all appearance of sharpness gene- 
rally disappears: the scale measurements must therefore be 
looked upon as approximate only ; the centre of each band may 
be taken as accurately determined within the unavoidable errors 
of experiment, but it is impossible to define their edges with 
much precision. The bands are seen much sharper when the 
current first passes than after the current has been passing for 
some time and the earth has become hot. On cooling, the sharp- 
ness of the bands re-appears. 
As a general rule, the purer the earth the sharper the band, 
and when impurities are removed to the utmost extent, the 
sharpness is such as to deserve the name of a line. This may be 
illustrated by mixing together yttria and lime. Lime phos- 
phoresces with a continuous and yttria with a discontinuous — 
spectrum. Mixed together, the phosphorescing energy of the 
lime does not spend itself over the whole spectrum, but concen- 
iS 
Ow 
f \ 
(ne = 
Fic. I. 
trates itself in greatly reinforcing the yttria bands. A molecule 
of yttria vibrating with a definite wave-length gives a nearly 
sharp line, but the molecule of lime with which it is weighted 
has no special tendency to vibrate to one wave-length more than 
another. The yttria induces the right vibration in the adjacent 
molecule of lime; but this lime, once set in vibration, cannot 
confine itself to the exact wave-length required, and overflows a 
little on each side, and the result is a widening and blurring of 
the bands, becoming greater in amount as the extraneous earth 
increases in quantity. 
To this rule one exception occurs. The body which I have 
named Sé, or 609, is remarkable for the great sharpness of its 
phosphorescent line, and I have noticed scarcely any variation 
in its sharpness, however large the bulk of extraneous earth 
associated with it. This line, however, is sharper and brighter 
when the currert is first turned on than it is after the earth has 
been phosphorescing for a minute or so. 
In the Bakerian lecture on yttrium delivered before the Royal 
Society (PAz/. Trans. Part 3, 1883), I described the phosphor- 
escent spectrum given by this element, and in the address which 
I have had the honour of delivering before this Section I gave a 
drawing of the spectrum of yttrium, together with a sketch of 
the train of reasoning by which I had been led to the opinion 
that excessive and systematic fractionation had split up this stable 
molecular group into its components, distributing its atoms into 
several groups, with different phosphorescent spectra. 
No longer than twelve months ago the name yttria conveyed 
a perfectly definite meaning to all chemists. It meant the oxide 
of the elementary body yttrium. I have in my possession speci- 
mens of yttria from M. de Marignac (considered by him to be : 
purer than any chemist had hitherto obtained), from M. Cléve | 
(called by him ‘‘purissimum”’), from M. de Boisbaudran (a 
sample of which is described by this eminent chemist as ‘‘ scarcely 
