THE APPLICATION OF SPECTRAL ANALYSIS TO PHARMACY. 1351 
The object of my present paper is not to explain the bright lines of incan- 
desceht bodies, but the appearances of solutions and other liquids when subjected 
to spectral observation. 
When certain solutions are thus observed, they show that part of the trans¬ 
mitted light is absorbed, giving rise to shadow-like bands called “absorption 
bands.” 
These bands are constant and give a spectrum peculiar to each preparation, as 
I will presently endeavour to show by exhibiting and explaining the appearances 
of many of the well-known articles of the Pharmacopoeia. 
Most solutions when greatly diluted are said to be transparent, but this is 
only comparatively correct. Even air and water deprive the solar light of some 
of its rays during its passage through these media. The more coloured the solu¬ 
tion, the more decided is the effect produced. 
Thus an ammoniacal solution of cupric sulphate will transmit the red and 
violet rays, and absorb all the rest. 
An ammoniacal solution of nickel will absorb the violet, but allow the blue 
and red to pass. 
A solution of ferric sulphocyanide will only transmit the yellow and red, 
while the green, blue, and violet are totally absorbed. 
Many substances forming nearly colourless solutions, yet afford very strong 
absorption bands, e. g ., the salts of didymium, manganese, bjematine, cr 
cruorine. 
The absorptive powers of fluid spectra explain the bluish haze of a distant 
landscape and the green colour of deep water. 
The spectroscope used in these experiments is one made by Mr. Ladd, of 
Beak Street. It is a very excellent instrument, reliable and easily worked. 
To use it, the eyepiece by itself is inserted into the tube of a microscope, the 
slit between the lenses opened and the object focussed. The tube containing 
the prisms is then replaced and the slit gradually closed till a good spectrum is 
obtained. Should any part of the spectrum not be clear, it must besfoeussed 
by means of the milled head attached to the eye lens. 
An indispensable addition to the microspectroscope is a small side prism 
which enables the observer to see the spectra of two solutions at the same time. 
Strict attention must be paid to the strength of the solutions under examina¬ 
tion. If too strong, too much light will be absorbed, and instead of well-marked 
lines, large, cloudy and obscure bands will be seen. 
Mr. Gladstone (Q. J. Chem. Soc. 1079) used wedge-shaped vessels, so that he 
could examine any thickness of the fluid, for the darker auy solution is, the 
thinner must be the stratum, and the weaker the solution, the deeper the stratum. 
This will be apparent from the diagram. 
I prefer a bit of glass tube, because more generally at hand and easily made. 
A common 1 oz. or ^oz. phial will answer well, or, what is still better, the little 
tube bottles used by the homoeopathic chemist. The tubes I usually employ 
are about fths of an inch in diameter. 
The solution or tincture is diluted till the spectrum is most advantageously 
seen. The rate of dilution varies from two to ten times or more. For instance, 
Tinct. Hyosc. Bienn. would require three or four times its volume of proof 
spirit, while Tinct. Caunab. Ind. is so dense and opaque to light that ten vols. 
of spirit would be necessary to show its beautiful spectrum to the greatest ad¬ 
vantage. As the dilution proceeds, the finest and faintest lines disappear, and 
afterwards the darkest. A few trials will soon point out the most effective 
strength to be employed. 
The advantage arising from the use of the wedge-shaped cells is now apparent, 
because by raising or lowering the stage of the microscope, a thicker or thinner • 
stratum of the solution may be viewed. 
