114 Trowbridge and Sabine — Steam in Spectrum Analysis. 



Art. XIII. — On the use of Steam in Spectrum Analysis ; by 

 . John Trowbridge and W. C. Sabine. 



Among the difficulties with which the investigator in spec- 

 trum analysis must contend is that of obtaining a source of 

 light which is free from constituents other than those which are 

 under examination ; and at the same time sufficiently powerful 

 to enable him to photograph the spectra of the latter. The 

 voltaic arc gives a sufficiently strong light to enable one to pho- 

 tograph throughout the visible spectrum ; the electric car- 

 bons, however,' are full of impurities, and it is difficult to in- 

 terpret the spectra obtained by these means. Moreover, it is not 

 easy to employ the arc spectrum for researches in the ultra 

 violet portion of the spectrum. On the other hand the spark 

 from a Ruhmkorff coil taken between terminals of metals, the 

 spectrum of which we wish to examine, gives us in general 

 spectra comparatively free from impurities, but its light is very 

 feeble compared with that of the electric arc, and even when 

 the spark is obtained by means of a powerful coil which is ex- 

 cited by an alternating dynamo machine an hour is necessary 

 to obtain with a concave grating of 21 feet radius of curvature, 

 on the most sensitive dry plate a photograph of the ultra violet 

 spectra of copper at the wave length 2100. 



It becomes an important question then to ascertain whether 

 the time of exposure of the sensitive plate can be shortened 

 by any process ; for the outlay in obtaining one photograph in 

 the ultra violet by the means hitherto at our command is very 

 large, involving as we have said the running of an engine of 

 at least two horse power for an hour. In our experiments 

 with a jet of steam we find that the time of exposure of the 

 sensitive plate can be shortened to at least one-third. 



We were led to employ steam for the purpose of obtaining 

 the spectra of oxygen and hydrogen with a more powerful 

 electrical excitation than is possible in Geissler tubes. During 

 the winter of 1886, when engaged upon the subject of oxygen 

 in the sun, one of us in connection with Mr. 0. C. Hutchins 

 tried to obtain a powerful electric spark in an atmosphere of 

 steam, but the experiments were unsatisfactory. The difficul- 

 ties were chiefly in the way of proper insulation. Experi- 

 ments showed that no containing vessel could be employed for 

 the sides of the vessel conducting the electricty from one ter- 

 minal of the KuhmkorfF coil to the other. Ko spark could be 

 obtained, and the experiments were abandoned. During the 

 present winter the experiments were renewed. ' The contain- 

 ing vessel was abandoned and the jet of steam was allowed to 



