§ 39-] SPECTROSCOPIC APPEARANCES OF BLOOD. 63 
Oscar Brasch 1 has within the last few years studied spectroscopy in 
relation to the alkaloids and organic poisons. Some of these, when 
mixed with Froehde’s reagent, or with sulphuric acid, or with sulphuric 
acid and potassic dichromate, or with nitric acid, give characteristic 
colours, and the resulting solutions, when examined by a spectroscope, 
for the most part show absorption bands ; these bands may, occasion¬ 
ally, assist materially in the identification of a poison. By far the best 
apparatus is a micro-spectroscope of the Sorby and Browning type, to 
which is added an apparatus for measuring the position on a scale of 
the lines and bands. Seibert and Kraft of Wetzlar make an excellent 
instrument, in which a small bright triangle is projected on the 
spectrum ; this can be moved by a screw, so that the apex may be 
brought exactly in the centre of any 
line or band, and its position read 
on an outside scale. The first thing 
to be done with such an instrument 
is to determine the position on the 
scale of the chief Fraunhofer lines, 
or of the more characteristic lines of 
the alkalies and alkaline earths, 2 the 
wave lengths of which are accurately 
known. If, now, the scale divisions 
are set out as abscissse, and the wave 
lengths in millionths of a millimetre 
are made the ordinates of a diagram, 
and an equable curve plotted out, as 
fully explained in the author’s work 
on Foods , it is easy to convert the numbers on the scale into 
wave lengths, and so make the readings applicable to any spectro¬ 
scope. For the purpose of graphical illustration the curve method 
is convenient, and is adopted in the diagrams, all taken from Oscar 
Brasch’s monograph. Where the curve is highest, the absorption 
band is thickest ; where the curve is lowest, there the band is 
weak. The fluid to be examined is simply placed in a watch- 
glass, the watch-glass resting on the microscope stand. 
1 Ueber V erivendbarlceit der Spectroscopie zur Unterscheidung der Farbenrecictionem 
der Gifte im Inter esse der forensischen Chemie, Dorpat, 1890. 
2 The alkalies and earths used for this purpose, with their wave lengths, are as 
follows :—KC1, a line in the red A 770, in the violet A 404. Lithium chloride, red line, 
670-5 ; sodium chloride, yellow, 589 ; strontium chloride, line in the blue, 461. It 
is also useful to measure the green line of thallium chloride=535. 
Collie, Proc. Roy. Soc., lxxi. 25, 1902, recommends a vacuum tube charged with 
hydrogen, helium, and mercury vapour ; this gives no less than 15 lines from the red 
He (706-53) to H in the violet (434-1). 
