Chemiluminescence 45] 



when a luminescence like the tail of a comet appeared. Only gases 

 containing oxygen gave the effect, which Dewar attributed to ozone 

 because starch iodide paper was darkened near the luminescence.^® 

 It is possible that active nitrogen was partly responsible for the light 

 in this particular experiment. Ozone excites persistent luminescences 

 in sulphur, iodine, sodium, and other metals. 



The origin of the light which appears when gases containing 

 ozone come in contact with liquids, reported by E. Fahrig (1890) 

 and E. Ritsert (1890), is subject to some doubt. In 1898 M. Otto 

 made a careful study of the luminescence of ozonized air or oxygen 

 bubbled through tap water. He found that there was no light if 

 the water was carefully purified. The light was particularly bright 

 in milk or urine, and Otto came to the conclusion that oxidation 

 of organic material was responsible. Ozone will cause luminescence 

 of chemiluminescent substances (like pyrogallol or aminophthali- 

 chydrazid) in solution, but in the case of Otto's tap water experi- 

 ments, the decomposition of gaseous ozone in contact with organic 

 material may have been the source of the luminescence, analogous 

 to the light from decomposition of ozone at high temperature. 



Another interesting action of ozone is its ability to cause lumi- 

 nescence of Sidot-blend (ZnS) , observed by F. Richarz and R. 

 Schenck (1903) . Ozone also causes formation of the latent image 

 of a photographic plate and a charged electroscope becomes dis- 

 charged in its presence. In fact its behavior is so similar to that of 

 radium that during the early part of the twentieth century a num- 

 ber of papers were published referring to the " emanation " from 

 reactions involving formation of ozone (see F. Richarz and R. 

 Schenck, 1903, 1904). 



Finally, we come to the chemiluminescences which take place in 

 the so-called " cold flames," a name used to distinguish them from 

 the incandescence of carbon particles in hot oil or gas flames, and 

 also from the characteristic emission of metals, which is responsible 

 for various colors in the Bunsen flame, the pyroluminescences. It 

 is practically impossible to state who first observed a particular cold 

 flame, but they received considerable attention in the last half of 

 the nineteenth century. For example, the blue flame of ether at 260° 

 was studied by W. H. Perkin (1882) who remarked that it was seen 

 by H. Davy." This flame does not burn paper and the ether itself 

 is not ignited. 



^"J. J. Thomson (1893: 184) has called attention to the phosphorescent glow in 

 vacuum tubes containing oxygen after electrical excitation, which he has attributed 

 to decomposition of ozone. 



"Davy (1811) noted the green light of chlormonoxyd on sudden decomposition. 



