424 
SIR W. CROOKES ON 
THE PHOTOGRAPHIC SPECTRA OP 
METEORITES. 
being’ faint or strong according to the general character of the spectrum. But in 
three, Bustee, El Nakhla, and Aubres, while the iron line shows as usual, the nickel 
line is either absent altogether or very faint.* 
In several of the aerolites in my list, it will be seen that the total number of lines 
recorded is below the average. The aerolite Bustee is an instance, t The rapidity 
with which it burnt away in the arc prevented me from giving the length of time for 
each exposure necessary to bring out many of the fainter lines. A rather interesting 
point came out in connection with this aerolite. 
In the early work my stock of material amounted only to about 2 gran—-and the 
length of time given for an exposure was necessarily short—it was noticed that 
although the stronger chromium lines came out in good intensity, the nickel lines 
were absent. Having obtained more material I was able to get photographs with 
longer exposures ; the nickel lines could then be seen, although as a whole much more 
faintly than those due to chromium. This gave rise to some experiments upon the 
relative photographic intensity of the two metals under the conditions in which I 
was working. 
The chromium spectrum is fairly rich in lines. Under the conditions prevailing in 
these experiments, in addition to a large number of faint lines there are recorded 
about one hundred strong ones, and of these there are three groups, which might be 
called the dominant lines of the element; the strongest of these groups is composed 
of the three lines at A 4254'50, A 4274'97, and A 4289'90 ; the next strong group is 
also three lines at A 3578'840, A 3593‘633, and A 3605'478, and the faintest consists of 
two lines, A 4862’02 and A 4870'9. 
Some pure chromium was taken and reduced to powder, some pure electrolytic 
nickel was prepared in the same way, and a mixture was made of silver, kaolin, and 
yttria, with 10 per cent, each of Ni and (Jr. This was pressed into a button and the 
spectrum taken as in the case of the aerolite : it was at once seen that the chromium 
groups came out in greater intensity than the adjacent nickel lines. 
The mixture above referred to is the outcome of many experiments made to find 
a material capable of carrying small percentages of nickel and chromium, so that 
when mixed with silver and formed into electrodes for the arc it should behave 
in a way similar to an aerolite ; the yttria was only used as a diluent of known 
composition.! 
An extensive series of experiments was carried out to throw light upon the 
* In connection with this proportionality between the lines of iron and nickel, I have examined the 
spectra of a number of siderites, and in the majority of instances the proportionality remains constant; 
but there are a few cases in which the nickel line is fainter than that of iron and others in which it is 
stronger. 
t Through the kindness of the Trustees of the British Museum and of Dr. Prior, three successive 
portions of this aerolite, making 12-171 grm. in all, were placed at my disposal. 
; Incidentally, I may say that this is a very convenient method for obtaining the arc spectra of the 
rare earths. 
