a a 
Fuly 23, 1885] 
NATURE 
285 
spread over it. The red band has likewise almost disappeared 
in the greater brightness of the continuous red of the calcic spec- 
trum. The double orange band is still very prominent, and the 
black space, 2942, between it and the green is very marked. 
The next mixture, one part of samarium to 500,009 parts of 
calcium, gives a spectrum which is fainter than the last, but the | 
The blank space 
between the yellow and green is strongly marked, but narrower | 
orange bands are still distinctly visible. 
than before. 
A mixture of one part of samarium in 1,000,coo parts of 
calcium was next subjected to experiment. In this the samarium 
spectrum is very feeble, and the orange bands are only to be 
seen with difficulty. Now the most striking characteristic of 
this spectrum is the black space which still cuts out the greater 
portion of the yellow. 
A mixture of one of samarium in 2,500,000 parts of calcium 
was now taken. 
bands of samarium have entirely gone, and its presence now is 
apparent only by the darkening in the yeilow portion of what 
otherwise would be a continuous spectrum. - 
The calcium phosphorescent spectrum by itself is continuous, 
with no break, lines, or bands in it. 
Jee : 
The Anomalous Line —2693.—On several occasions I have 
x 
spoken of an orange line, 2693, which by its brilliancy and 
sharpness is a prominent object in most of the samarium-yttrium 
spectra. With pure samaric sulphate it is exceeding faint. With 
samaria containing 5 per cent. of yttria it is very little brighter ; 
with ro per cent of yttria it gains a little ; with 15 per cent. it is 
brighter still, and with a mixture of 80 parts samaria and 20 
parts yttria it is at its maximum intensity. It continues to be 
the most striking feature in the spectra of the various mixtures 
of samaria and yttria until the proportion becomes samaria 3, 
yttria 97, when it begins to get less bright, and only when pure 
yttria is reached does it altogether vanish. 
It is noteworthy that so long as this bright line is a component 
of the spectrum, the other bands manifest decidedly less intensity, 
and many of them are suppressed. The profound modification 
in the spectra of samaria and yttria developed by their mixture 
is, I believe, without precedent in spectrum analysis. It is 
difficult to realise the character of the modification which con- 
verts somewhat faint diffused bands into one intensely sharp and 
brilliant line. 
One important lesson taught by the many anomalies unearthed 
in these researches is that inferences drawn from spectrum 
analysis fer se are liable to grave doubt, unless at every step the 
spectroscopist goes hand in hand with the chemist. Spectro- 
scopy may give valuable indications, but chemistry must after all 
be the court of final appeal. 
The following paper (reprinted from the Chemzcal News) is so 
intimately connected with Mr. Crookes’s work, that it may be 
appropriately appended to his paper :— 
Ar the meeting of the Académie des Sciences on June 8, 
1885, M. Lecoq de Boisbaudran requested that a sealed 
packet which he had deposited June 30, 1884, might be opened. j 
The packet was opened by the Permanent Secretary during the 
meeting, and contained the following note :— 
*“When the electric spectrum of a solution wth a metallic 
dase is produced it is customary to make the outside platinum 
wire (whence the induction spark strikes) positive, the liquid 
consequently forming the negative pole.1 If the direction of 
the current is reversed, the metallic rays (due to the free metal 
or to one of its compounds) are scarcely or not at all visible, at 
at all events so long as the exterior platinum wire now forming 
_the negative pole is not coated with a deposit. 
‘* Having again last year taken up my researches on the rare 
earths belonging to the didymium and yttrium family, I had 
occasion to observe with many of my preparations the formation 
of spectrum bands, nebulous, but sometimes tolerably brilliant, 
having their origin in a thin layer of a beautiful green colour, 
which was seen to appear at the surface of the liquid (a solution 
of a chloride) when it was rendered ositzve. 
“These are the approximate positions of the principal 
bands :— 
* This rule, hitherto general for »efad/ic solutions, is not always applicable 
to liquids containing me¢al/o‘d bodies, as I haye already had occasion to 
notify (see my ‘‘ Spectres Lumineux,” p. 38). 
In the spectrum shown by this mixture the | 
Observations 
A narrow band, somewhat 
hazy. Rather faint. 
About 14 divisions wide. 
(Due to calcium ? ?) 
A nebulous band slightly 
connected with the fol- 
lowing one. About 3 
divisions wide. Slight 
intensity, but generally 
stronger than 913. 
A nebulous band. Inten- 
sity varying with the 
state of the liquid and 
strength of spark. It 
seems to be fainter in 
the earths obtained 
from the sulphates 
which are very slightly 
soluble in potassic sul- 
phate than in the earths 
obtained from the more 
soluble double  sul- 
phates. In some cases 
it has been seen as 
brilliant as @ 1154, but 
it has almost always 
been seen muck more 
feeble than 115} in the 
earth obtained from the 
very slightly soluble 
double sulphate. It 
has, indeed, on several 
occasions been seen 
fainter than Iot. 
A nebulous band, shading 
off from right to left. 
Rather strong, and gene- 
rally much the most 
brilliant in the spectrum 
of the yellow’ earth 
whose double potassic 
sulphate is very slightly 
soluble. 
A very hazy band, appear- 
ing somewhat shaded 
from right to left when 
the spectrum is brilliant. 
About 4 or 44 divisions 
wide. Somewhat joined 
to the following. Gene- 
rally of very moderate 
intensity. 
476% Faint band, very hazy. 
About 6 divisions wide. 
Micrometer 
gIf About the 6204 
middle. 
Iol Approximately 
about the 
middle. 
104;5; Approximately 573 
about the 
middle. 
From ) 
111s 
to 
112 
115} 
About the be- 
ginning. Very 
indistinct. 
About the mid- 
dle of maximum 
of light. 
About the end. 
Very indistinct. 
Apparent 
centre. 
5435 
117 
About 
I4It 
487 
About 
147% 
to 
1472 ) 
‘On comparing in the different products the relative in- 
tensities of this new reversion spectrum and of the already 
known direct rays, I have come to the conclusion that the body 
producing the band a115% is very probably of one of the 
following :— 
“Didymium, erbium, Ya (of M. de Marignac), lanthanum, 
samarium, zirconium, scandium, thulium, ytterbium, yttrium. 
** Cerium and thorium are also excluded for chemical reasons. 
«7 have not yet obtained the new spectrum with a substance 
altogether free from holmium, but I have good reasons to think 
that this metal is not the cause of the observed phenomena. 
‘The treatment undergone by the earths which give most 
sharply the reversion spectrum hardly admits in my preparati »ns 
of the presence of such bodies as phosphoric, boric, &c., acicls. 
‘*The band a 1154 (and most of the others which, except per- 
haps the band 104;%, follow in their intensities the same varia- 
tions as a 1154) appears, therefore, only to be attributable to 
terbia, unless, indeed, it be due to some new analogous earth 
not hitherto defined.+ 
‘* The treatment of a yellow earth obtained from samarskite, 
and much resembling that which is now called ¢erdia, has already 
Apparent 
centre. 
t There remains to be examined the earth decipia (of M. Delafontaine), 
ai existence of which appears to be confirmed by the researches of M. 
eve. 
