= 3 Ae 
‘ . 
Fuly 23, 1885 | 
dependent upon it. Happily the country is now beginning to 
realise the importance of the matter, and when the Government 
places at the disposal of the Board sufficient money to carry on 
the necessary investigations, the produce of the Scottish fisheries, 
great as it now is, may be still largely increased. 
RADIANT MATTER SPECTROSCOPY 
a HE following paper on this subject was read by Mr. Crookes 
at the Royal Society, June 18 :—- 
In the concluding sentence of the Bakerian lecture which I 
had the honour to deliver before the Royal Society, May 31, 
1883, I said that the new method of radiant matter spectroscopy 
there described had given me not only spectrum indications of 
the presence of yttrium as an almost invariabl2, though very 
minute, constituent of a large number of minerals, but had like- 
wise revealed signs of another spectrum-yielding element. I 
stated that I had repeatedly seen indications of another very 
beautiful spectrum characterised by a strong red and a double 
orange band. 
Elimination of Mercury Vapour from Vacuum Tubes.—It is 
much more difficult than is generally supposed to keep mercury 
vapour from diffusing into the experimental tubes. 
The following plan answers perfectly so far as my experiments 
have yet gone :—Sulphur is first prepared by keeping it fused 
at a high temperature till bubbles cease to come off, so as to get 
rid of water and hydrogen compounds. It is then allowed to 
cool, and is pounded and sifted so as to get it in the form of 
granules averaging a millimetre in diameter. A glass tube, a 
centimetre in diameter and about 2 feet long, is lightly packed 
for half its length with this sulphur, and next about 2 inches of 
iodide of sulphur (I,S,) is added, and the rest of the tube is 
then filled up with sulphur. Ignited asbestos is packed in at 
each end to keep the sulphur from blowing out whilst the 
vacuum is being made, or from being sucked through when air 
is suddenly let in. This contrivance entirely keeps mercury 
vapour from passing through, since the iodide of sulphur holds 
its iodine very loosely, and fixes the mercury in the form of non- 
volatile red iodide. A glass tube containing finely-divided copper 
must follow in order to keep the sulphur out. With this block- 
ade interposed between the pump and experimental tubes I have 
been unable to detect mercury vapour in any of the tubes, 
whether in the cold or on heating them. 
The “Orange Band” Spectrum.—Since the date of my last 
paper I have devoted myself to the task of solving the problem 
presented by the double orange band first observed in 188. 
With the yttrium experience as a guide it might be thought that 
this would not be a difficult task, but in truth it helped me little 
beyond increasing my confidence that the new, like the old 
spectrum, was characteristic of an element. The extreme sen- 
Sitiveness of the test is a drawback rather than a help. To the 
in -xperienced eye one part of ‘‘ orange band” substance in ten 
thousand gives as good an indication as one part in ten, and by 
far the greater part of the chemical work undertaken in the hunt 
for the spectrum-forming element has been performed upon 
material which later knowledge shows does not contain sufficient 
to respond to any known chemical test. 
Chemistry, except in few instances, 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°99, the odd ovor per cent. is conveniently put 
down to “impurities,” ‘‘loss,” or *‘ errors of analysis.” When, 
however, the 99°99 per cent. constitutes the impurity and this 
exiguous 0’OI 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, isa fiction, and separation by precipitants 
is nearly impossible. 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 by the solubility of nearly all precipitates in 
water or in ammoniacal salts, when present in traces only. 
What is here meant by ‘‘ traces” will be better understood if I 
give an instance. After six months’ work I obtained the earth 
didymia in a state which most chemists would call absolutely 
pure, for it contained probably not more than one part of im- 
purity in five hundred thousand parts of didymia. But this one 
part in half a million profoundly altered the character of didymia 
from a radiant matter spectroscopic point of view, and the per- 
sistence of this very minute quantity of interfering impurity 
NATURE 
283 
entailed another six months’ extra labour to eliminate these final 
. and to ascertain the real reaction of didymia pure and 
simple. 
Chemistry of the Orange Band-forming Substance.—At first it 
was necessary to take stock, as it were, of all the facts regarding 
the supposed new substance, provisionally termed x, which had 
turned up during the search for the orange band. In the first 
place x is almost as widely distributed as yttria, frequently occurr- 
ing with the latter earth. It is almost certainly one of the earthy 
metals, as it occurs in the insoluble oxalates, in the insoluble 
double sulphates, and in the precipitate with ammonia. It is 
not precipitated by sodic thiosulphate, and moreover it must be 
present in very minute quantities, since the ammonia precipitate 
is always extremely small, and as a rule «x is not found in the 
filtrate from this precipitate. 
At this stage of the inquiry the chemical reactions of x were 
much more puzzling than with yttria. At the outset an anomaly 
presented itself. The orange band was prone to vanish in a 
puzzling manner. Frequently an accumulation of precipitates 
tolerably rich in x was worked up for purposes of concentration, 
when the spectrum reaction suddenly disappeared, showing itself 
neither in precipitate or filtrate ; whilst on other occasions, when 
following apparently the same procedure, the orange band be- 
came intensified and concentrated with no apparent loss. The 
behaviour of the sulphate to water was also very contradictory ; 
on some occasions it appeared to be almost insoluble, whilst 
occasionally it dissolved in water readily. 
Zs “x” a Mixture?—A very large series of experiments, 
which need not here be described in detail, resulted ultimately 
in establishing the remarkable fact that the + I sought was an 
earth which of itself could give no phosphorescent spectrum in 
the radiant matter tube, but became immediately endowed with 
this property by admixture with some other substance, which 
substance likewise by itself had no power of phosphorescing with 
a discontinuous spectrum. 
x’ tn Cerite.—In the corresponding yttrium research I was 
aided materially by the fact that the sought-for earth did not 
give an absorption spectrum. This enabled me to throw out a 
large number of obscurely known elements, and I therefore early 
endeavoured to ascertain whether the supposed new earth, x, did 
or did not give an absorption spectrum. Gradually it was noticed 
that whenever the didymium absorption bands were strong, the 
orange band spectrum was also particularly brilliant. Moreover, 
amongst the earths previously enumerated as mixed with lime in 
the quest for x, I have mentioned that some of them gave the 
orange band spectrum with increased intensity ; the earths of 
the cerium group were the most noteworthy, and these con- 
siderations made it probable that here would be found the loca- 
tion of x. 
Ax=%ysts of Cerite—The cerium group consists of cerium, 
lanthanum, didymium, and samarium. 
The first necessity was to get the earths ceria, lanthana, and 
the mixture hitherto called didymia, in a pure state ; for my so- 
called pure earths of this group all showed the orange band in 
more or less degree. 
The separation from each other of ceria, lanthana, didymia, 
and samaria is a most laborious process, and the amounts of 
these earths, obtainable in anything like a pure state, is small, 
compared with the mass of material worked up. Full particulars 
are given in the paper as to the method adopted to obtain each 
of them in a state of purity. 
Ceria.—The ceric oxide obtained was almost pure white. A 
considerable thickness of a strong solution did not show a trace 
of absorption spectrum. The atomic weight of the metal was 
taken and yielded the number 1411. 
The ceric oxide gave no orange band spectrum in the radiant 
matter tube, either with or without the addition of lime. 
Lanthana.—Lanthana is more difficult to purify than ceria. 
Long after the lanthana appeared pure it gave in the radiant 
matter tube a good orange band spectrum when mixed with lime 
and treated as usual, although without lime it gave no spectrum. 
Ultimately, however, a lanthana was obtained which, mixed 
with lime and treated in the usual manner, gave no orange band 
spectrum whatever. This lanthana was snow-white, and had 
an atomic weight of 138°3. 
Didymia.—The earth formerly called didymia is now known 
to be a mixture of didymia and samaria, and systematic opera- 
tions were now commenced with the object of obtaining the 
didymia and the samaria in a state of purity—that is to say, in 
such a condition that one of them should show no orange band 
