The Persistence of the Spectrum of Carbon Monoxide

THE letter of Dr. Carl v. Wesendonk (p. 29), which gives an account of the spectrum of carbon monoxide appearing in a vacuum tube containing silicon tetrafluoride, affords an instance of the extreme difficulty of obtaining vacuum tubes charged with perfectly pure substances. The case he cites of silicon fluoride being prepared from “pure” sulphuric acid, glass and fluor spar, without any but glass joints to connect the different parts of the apparatus, is one in which neither the perfect freedom of the sulphuric acid, nor of the glass itself, from carbon compounds can be relied upon. In experiments on the absorption spectrum of ozone made by me in 1881, it was found that strong sulphuric acid free from all the usual impurities was not absolutely clear, but by being kept in an atmosphere containing a large proportion of ozone it became perfectly brilliant and absolutely colourless when seen in volumes of half a gallon to two gallons at a time. It appeared from further experiments that the impurities were either carbon or some form of organic matter probably coming from dust or dirt. As to the purity of the glass used for vacuum tubes, it may be remarked that dust and condensed vapour from carbonaceous matter, such as the products of combustion from lamp oil or coal, adheres to its surface with much tenacity. It is probable that the fluor spar contained organic matter, for the reason that this substance is associated with limestone of a bituminous character in England and that it has been asserted that its colour is due to organic substances. By the action of sulphuric acid a gaseous carbon compound might easily be evolved which would contaminate the silicon fluoride even if there were no carbonates present. Next we have to consider the traces of air which may remain in the tube, and must not regard these as being absolutely free from hydrocarbons. M. Armand Gautier has shown that there are combustible gases in the atmosphere, one of which is a hydrocarbon, the other hydrogen, and there is also some carbon monoxide. The difficulty of removing these by ordinary chemical treatment is so great that special operations and reagents were provided for their removal.