Demonstration 22

Barking Dog

            The reaction of nitrogen monoxide, NO, (or nitrous oxide, N₂O) with carbon disulphide is similar to the well-known hydrogen-oxygen reaction, but is accompanied by a characteristic “barking” sound.  A mixture of nitric oxide and the vapour of carbon disulphide, contained in a long tube, is ignited.  The combustion wave travels at a moderate rate down the tube compressing the gas ahead of it.  At a certain distance, dependent on the diameter of the tube, the residual mixture explodes [1].  In a very long tube the passage of the explosion wave may be seen.†  This reaction also produces a considerable amount of very bright blue light and is one of few examples of chemical luminescence in the gas phase.

            Carbon disulphide reacts with nitrogen monoxide forming nitrogen, carbon monoxide, carbon dioxide, sulphur dioxide and sulphur.

3 NO + CS₂==> ³/₂ N₂ + CO + SO₂ + ¹/₈ S₈                              (22.1)

4 NO + CS₂==> 2 N₂ + CO₂ + SO₂ + ¹/₈ S₈                              (22.2)

            The reaction between carbon disulphide and nitrogen monoxide was carried out by Liebig in 1853 during an evening lecture [2].  The audience was so enthusiastic about this experiment that Liebig repeated it; this time there was a violent explosion.  The Queen of Bavaria was wounded in the cheek.  It is possible that in the second experiment nitrogen monoxide was contaminated with oxygen (which formed nitrogen dioxide).  Liebig wrote to Wöhler in Göttingen:

As I Looked around after the terrible explosion in the room where the audience sat, and saw the blood running from the faces of Queen Therese and Prince Luitpold, my horror was indescribable; I was half dead.  Fortunately, the accident had no further unpleasant consequences.  their Majesties behaved in a noble and high-minded way, and all of their concern seemed to focus itself only on me.  The Queen sent her personal physician to me that very evening, and every day their majesties inquired with respect to my health.  Old King Ludwig himself came the next day and asked if my wound was serious, and when I said No he exclaimed: Then everything is all right; so long as nothing happened to you, the rest is nothing...

            Some twenty years later (1873) a German patent was taken on the use of this process as a “possible source of light for photography at night”.  We have successfully photographed ourselves on ‘daylight’ balanced colour film using the light of the ‘Barking Dog’ in an almost dark lecture theatre.  The film had a colour temperature balance or 5500 K which means that it will give a correct colour rendering when the light has the same spectral quality as light emitted incandescently from a ‘black body’ at that temperature.  However, there is an overall blue cast on our pictures which indicates that the colour temperature of the chemiluminescent emission from the ‘Barking Dog’ was in excess of 5500 K. In photography this ‘black body’ (incandescent equivalent) emission is known as ‘colour temperature’. The colour temperature of a light source is closely related to the ratio of the intensities of the blue and red light. Daylight type colour film has a colour temperature rating of around 5500K,^* which means that it will give the correct colour rendering when exposed to light that has the same spectral quality as light that would be emitted incandescently from a ‘black body’ at that temperature. The surface temperature of the sun is around 6000K, and since some of the blue light is scattered in our atmosphere (that’s why the sky is blue) the light reaching ground level will have a slightly lower blue to red ratio, and so lower colour temperature.

‘Barking Dog’ light is ideal for exposing the monochrome silver halide based coatings, known as orthochromatic, because they are sensitive only to blue and ultraviolet light. However, in order to match the grey scale of monochrome film to the colour sensitivity of the human eye, sensitises have to be added to the light sensitive emulsions which are then referred to as panchromatic. This technique is analogous to the production of colours in our ‘Rainbow’ chemiluminescence experiment: Demonstration 26 (DNPO).

 

            Safety.  This experiment must always be carried out behind a protective screen.  CS₂ has a very low flash point and is highly toxic.  The tube must be filled in a well-ventilated hood.  Safety glasses must be worn!

 NO₂/N₂O₄ is very toxic and may cause inflammation of the lungs. Very insidious gas, exposure may cause little pain or go unnoticed, but the resulting edema several days later may cause death.

 

Appendix.

 

References.

1.    G. Fowles, Lecture Experiments in Chemistry, London, G.Bell & Sons, Ltd., 1947, p. 491.

2.    H.W. Roesky and K. Möckel, Chemical Curiosities, trans. T.N. Mitchel and W.E. Russey, New York, VCH Publishers, Inc., 1996, p. 254.

3.    B.Z. Shakhashiri, Chemical Demonstrations, The University of Wisconsin Press, 1986, vol. 1, p. 117.

4.    D.B. Reid, Elements of Practical Chemistry, Edinburgh, Maclachlan and Stewart, 1830, p. 172.

5.    F.G. Benedict, Chemical Lecture Experiments, New York, The Macmillan Company, 1919, p.217.

 

---