The absorption of light and the colours of natural bodies / by Professor Stokes.

  • Sir George Stokes, 1st Baronet
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: The absorption of light and the colours of natural bodies / by Professor Stokes. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    another in their mode of production, I hardly like to em- ploy it. You have seen in what manner you can readily, and'^j almost without any apparatus, observe a pure spectrum, and1! how it is modified by the interposition of a coloured body ; ’ and I may just mention one or two instances of interesting results which may he obtained in this manner. Sometimes . the mode in which a coloured medium attacks the different parts of the spectrum is highly characteristic of the particular | fluid that you are employing. Here, for example, is one very characteristic case—the red colouring matter of blood. The spectrum which that gives is represented in the upper part of this figure [referred to]. In order to see the spectrum nothing more is recpiisite than this : You take a slit of the roughest description—here is one made of wood and tinned iron blackened, and the blood is conveniently held in a test-tube, which you can-hold in position by an elastic band. In order to see the spectrum by transmission you have nothing more to do than to hold this against a source of light and look at it If you use, not a wedge-shaped vessel, but a test-tube, you cannot be sure of not passing over some of the most interesting parts of the phenomena, unless you go step by step, and use several different thicknesses, or, which comes to the same thing, different degrees of dilution. For instance, when a solution of blood is so highly coloured as this, a great part of the spectrum is cut off, and it may be that you will see nothing but a broad black band, whereas, if I had med a weaker solution or a test-tube of smaller diameter, I should have seen certain highly characteristic phenomena of absorption. In order to see these, the solution must be so diluted that it is little more than pink. Then you will see these highly characteristic dark bands of absorption. I know of no sub- stance which can be confounded with blood if you simply take the spectrum of it in this manner, unless possibly an out- of-the-way substance, turacine, the colouring matter found m the red feathers of the wings of the touraco, a bird found at the Cape of Good Hope. If you only looked at the spectrum in one condition, it is possible that the two might be con- founded, although hardly so ; but if you combine the obser- vation of one of these peculiar spectra with the observation of the effect of re-agents, you get a combination of characters which is such that it is almost impossible to confound any
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