Pottok & Lronarp—On the Spectra of Iron, &. 219 
any lines developed by the metals, but not by their solutions. 
Then in every case the last four spectra taken gave the gold 
electrodes long, with short lines between, of the spark spectra of 
solutions containing 1 per cent., ‘1 per cent., -01 per cent., -001 
per cent. of the element under examination. 
To distinguish briefly between the different phases of the lines, 
with diminishing concentration, use has been made of some of 
the letters of the Greek alphabet, with the following meanings :— 
= seen with the metal, but not with strong solutions. 
i 
nS i strong solutions, but not with 1 °/, solutions. 
in ” 1 le ” ” ” al oh » 
> Sia ” 1 we ” ” 3 “OL we ” 
i = Olses} Ss 5 ee is re “001% s ue 
w® = Bs ANON St 
No new measurements were attempted, the lines being identified 
by means of a finely graduated ivory scale, and the corresponding 
published lines tabulated. In the case of manganese, however, 
one of the residuary lines, A 2594-0, was not found in the tables 
at our disposal, and our own measurement is given. 
In the case of cobalt, Plate X VII., the solution was not diluted 
so abruptly, and this plate shows the gradual extinction of the ~ 
lines with diminishing concentration better than the others; but 
as the whole object was to find the residuary lines, one passes 
directly from a saturated solution to a solution containing only 1 per 
cent. of the element under examination, and then dilutes until the 
lines entirely disappear. In the case of chromium, silicon, 
manganese, and zine, all the dilutions are not given in the plates, 
as lines that can still be seen on the negatives cannot be seen in 
the reproductions at all, as will be obvious by comparing the 
tables with the plates. ven with 1 per cent. solutions, the lines 
do not come out by any means strongly with one minute’s 
exposure, and with ‘1 per cent. they are always very faint, 
and very few substances give lines that will show at all with 
‘001 per cent. 
Go.tp Execrropes. 
To facilitate the identification of the lines, some of the strong 
gold lines have been numbered, from 10 to 25, and their wave- 
