ON THE SPECTROSCOPE AND ITS 
APPLICATIONS 
VIII. 
I TOLD you I had something more to say about the 
spectrum of blood, and this is not only an instance 
of the way in which the spectrum helps us in several 
important questions that, at first sight, do not seem 
at all connected with each other, but it shows the 
enormous power of research that is open to us. The 
colouring matter of blood, for instance, is found, like that 
of indigo, to exist in two perfectly different states, which 
give two perfectly different spectra, The colouring matter 
of blood is indeed capable of existing in two states of 
oxidation, which are distinguishable by a difference in 
colour, and also in their action on the spectrum. They 
may be made to pass one into the other by suitable 
oxidising and reducing agents; they have been named 
by Professor Stokes, their discoverer, red and purple cruo- 
rine. Previous to the introduction of spectrum analysis, 
red and purple cruorine were perfectly unknown, Fur- 
ther, if by means of a spectrum microscope, such as I 
have already described, a blood-stain is examined, Mr. 
Sorby asserts that the thousandth part of a grain of blood, 
—that is to say, a blood-spot so small that it only contains 
yooo Of agrain, is perfectly easy of detection by means of 
this new method, and he has shown that its presence may 
be easily proved in stains that have been kept for a long 
time, and recognised even after a period of fifty years. 
oF 
t 
Fic. 46. Fic. 47- 
Tig. 46.—Steinheil’s slit, showing reflecting prism. Fig. 47.~Path of light 
through reflecting prism and into the slit. 
He has also shown how it may be detected under the most 
unfavourable conditions, provided that a trace of hamatin, 
has escaped decomposition or removal; he has, in fact, 
successfully applied this method in several important 
criminal cases. 
Another very interesting fact is, that when blood con- 
tains very small quantities of carbonic oxide gas in solu- 
tion, it exhibits a very curious series of absorption bands. 
This fact is of considerable value in toxicological research, 
for in cases of poisoning by the so-called charcoal fumes, 
where, as is well known, the poisonous action is due to 
the formation of carbonic oxide, it can be readily detected 
by the peculiar bands which the blood under these cir- 
cumstances exhibits. 
Mr. Sorby has also applied the spectrum microscope 
to the study of blow-pipe beads, and has shown that in 
some cases as small a quantity as ,,1,,th of a grain of 
some substances can be thus recognised, even when mixed 
with other coloured bodies, which would interfere with 
the usual reactions dependent on colour alone, 
In the case of radiation, as you know, we are able to 
determine the existence of new elements altogether, This 
is produced to a certain extent, as in the above case, in 
the absorption spectrum, Let me give you another prac- 
tical application of this principle. Dr, Thudichum, as a 
result of researches made for the Medical Department of 
the Privy Council, has communicated to the Royal Soc‘cty 
NATURE 
a paper in which he narrates the result of his inquiries on 
the yellow organic substances contained in animals and 
plants ; and at the present moment it is impossible to 
say what important practical results may be expected as 
we come to know more about these substances, especially 
in the matter of dyes, which I am sure is a thing that will 
commend itself to you. - 
Again, Mr. Sorby, in a communication to the Micro- 
scopical Society, brings the matter still nearer home, He 
shows us that, in the case of wines, he can, by means of 
the absorption bands, determine the very year even of 
vintage, and this, you will see at once, is a matter of very 
great importance. Let me read you an extract from one 
of Mr. Sorby’s reports. He says :—“‘ The difference for 
each year is at first so considerable that wines of different 
vintages could easily be distinguished; but after about 
six years, the difference is so small that it would be diffi- 
cult or impossible to determine the age to within a single 
year. After twenty years, a difference of even ten years 
Fic. 48-—Coincidence between the bright line given out by sodium vapour and the dark 
line produced by the absorption of sodium vapour. 
y ’ 
z 5 
does not show any striking contrast, and the age could 
not, therefore, be determined to nearer than ten years by 
this process. However, up to six years I think it quite 
possible to determine the age to within a single year, I 
took specimens of various ports from the casks, of different 
ages up to six or seven years, and labelled them in such a 
manner that I did not know the age of any, but could 
ascertain it afterwards by reference. I then made the 
experiments with great care, and found that, by proper 
attention to the details described above, I could correctly 
determine the year of vintage of each particular speci- 
men.” (Chemical News, December 17, 1869, p. 295.) 
We have, in fact, a definite method of analysis of 
animal and vegetable colouring matter, and also of the 
colouring matter of decayed wood. Nor is this all, for, 
in another communication—for these things are now be- 
ginning to crowd upon us, and they will continue to do so 
much more by-and-by—Dr. Phipson asserts that this 
new method is perfectly competent to indicate any ar i- 
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