24 
DES. J. PLUCKEE AND J. W. IIITTOEF ON THE 
finally rising from the hydrogen-spectrum transformed into a continuous one. Here 
the heat of the discharge is increased by the increased density of the vapour of 
water, and reciprocally the evaporation is accelerated by the rising temperature of the 
discharge. The vapour of water is decomposed by the discharge ; the ignited hydrogen 
resulting from the decomposition exhibits a spectrum at a lower temperature than the 
resulting oxygen does. After the discharge ceases, oxygen and hydrogen are recomposed 
again to water. 
64. Phosphorus , when treated like sulphur (35), exhibits a beautiful spectrum of the 
second order. Whatever may be the gradual change of the intensity of light produced 
by regulating as well the discharge as (by means of a lamp) the heat of the spectral 
tube, we get only one spectrum of bright lines successively developed. Among them 
there is one announcing at first sight the presence of vapour of phosphorus, a triple 
orange line, formed by two single lines of first intensity, and a third less bright one 
bisecting the interval between them. The other brightest lines are seen within the 
green. 
We get no difference at all by introducing into the spectral tube either common or 
red phosphorus. After the current had passed for some time, common phosphorus was 
seen, within the tube, transformed into a subtle powder of the red kind. 
65. Chlorine , Bromine , and Iodine were among the substances first submitted to spec- 
tral analysis by one of us. On resuming the subject we fully confirmed the formerly 
obtained results, that not any two of the numerous spectral lines, characterizing the 
three substances, were coincident. 
By means of the electric current we got in all instances only spectra of the second 
order. We were especially desirous of ascertaining whether there existed a spectrum 
of iodine, corresponding to a lower temperature, the inverse or negative image of which 
agreed with the spectrum produced by absorption on sending sunlight (which, in order 
to prevent the influence of Fraunhofer’s dark lines, may be replaced by the light of 
phosphorus in combustion) through a stratum of heated vapour of iodine. Thus, 
indeed, we obtain more than fifty shaded bands, the breadth of which decreases from 
the violet to the red, constituting a spectrum of the first order. The flame of hydrogen 
in open air was not fitted to ignite vapour of iodine introduced into it sufficiently. But 
by feeding the flame by oxygen we got a new spectrum. Large fields, shaded by dark 
transversal lines, differently bounded, but quite similar to the third type of the spectra 
of vapour of carbon, constituted a spectrum of the first order. But the spectrum we 
might have expected according to theory was not seen. 
66. Arsenic , when treated like sulphur and phosphorus, gives a well-defined spectrum 
of the second order. 
67. So does mercury when introduced into a spectral tube from which air is expelled, 
either by means of Geissler’s exhauster, or by boiling the mercury within it. After a 
slight heating of the tube by means of an alcohol-lamp the discharge passes; and 
having once passed, it continues to do so, even without the lamp. Vapour of mercury 
