In regard to the first of these experiments Traube[20] has carefully investigated what takes place when palladium hydrogen is allowed to remain in contact with water and oxygen. Hoppe-Seyler had noticed that under these conditions small quantities of hydrogen dioxide were formed, but he attributed this to the union of the active oxygen with the water. Traube, on the other hand, finds that in the formation of hydrogen dioxide under these circumstances there is nothing formed which has oxidizing properties, not even indigo sulphuric acid is oxidized. He shows by direct experiments that nascent hydrogen can not by its action on oxygen produce active oxygen or ozone. He finds the action of palladium hydrogen to be analogous to that of zinc and other metals, which when allowed to oxidize slowly in contact with air and water give rise to the formation of hydrogen dioxide. The process is to be regarded rather as a reduction of molecules of oxygen than as an oxidation of water. Traube represents the action by the following equations:—
He proves by direct experiments that no active oxygen is formed during this process, and points out that the oxidations observed by Hoppe-Seyler and Baumann must have been brought about by the hydrogen dioxide. But this would not account for the oxidation of carbon monoxide, for it has been previously shown by Remsen[21] that hydrogen dioxide cannot oxidize carbon monoxide, not even when it is heated to its point of decomposition. Traube[22] therefore repeats Baumann’s experiment, he finds that palladium hydrogen in the presence of water and oxygen does oxidize carbon monoxide; but as he had shown that no active oxygen was formed during the process, and as the hydrogen dioxide could not cause the oxidation, he concluded that the palladium itself must play an important role in the reaction. By further experiments he soon became convinced that there are two stages in the process. 1st the palladium hydrogen acting on water and oxygen forms hydrogen dioxide, 2nd the hydrogen dioxide in the presence of palladium oxidizes the carbon monoxide. Traube[23] introduced into a glass flask containing carbon monoxide a dilute solution of hydrogen dioxide and a small piece of palladium foil, previously ignited, the action was allowed to continue for 22 hours after which the CO was replaced by air free from carbon dioxide. After leaving the flask the gas passed through a solution of barium hydroxide; an abundant precipitate was formed, showing that in this case the quantity of carbon dioxide formed was greater than in the first experiment, in which he used palladium hydrogen, water, oxygen and carbon monoxide.
Traube’s conclusion is as follows:—
“The carbon dioxide obtained in Baumann’s experiments is not formed during the oxidation of the hydrogen of the palladium hydrogen, (there being formed by this action merely hydrogen dioxide and palladium free from hydrogen) but by the combined action of these last two substances on carbon monoxide.” “Therefore, the proof is given that the act of slow combustion (Autoxidation) has not in itself the power of making oxygen active.”
The conclusion reached by Traube was tested by Professor Remsen and myself in the following way: A current of carbon monoxide was passed through several wash bottles containing solutions of caustic soda, then through a wash bottle containing clear baryta water, then into a flask containing a solution of hydrogen dioxide, containing a slight excess of hydrochloric acid. The flask also contained a small piece of palladium foil free from hydrogen. After leaving the flask the gas passed through a solution of baryta water, which was protected from the air by a U tube containing solid KOH. It was only necessary to pass the carbon monoxide through for a very short time to obtain an abundant precipitate of barium carbonate. We also noticed that under these conditions the palladium foil was dissolved.
From these experiments it is clear that the oxidation phenomena which Hoppe-Seyler and Baumann attributed to active oxygen are really due to the combined action of palladium and hydrogen dioxide, and to suppose that atomic oxygen exists in the free state at any time during the process is entirely gratuitous.
It remained to test the second of Baumann’s statements; namely that carbon monoxide in the presence of moist phosphorus and air is oxidized to carbon dioxide by the active oxygen formed by the slow combustion of the phosphorus. Leeds[24] also has on record an experiment on this subject, in which he claims that under these conditions oxidation takes place. In taking up the subject, therefore, Prof. Remsen[25] and myself have taken the greatest care to avoid all sources of error. We tried the effects of passing air alone freed from carbon dioxide over moist phosphorus and then into clear baryta water, Baumann[26] states that this can be done, and the baryta water remains perfectly clear, even if the current of air is passed for six hours. We obtained a precipitate immediately. Thinking this might be caused by the white vapors which are formed during the process, we passed the gas after its exit from the vessel containing the phosphorus through a layer of previously ignited asbestos. The layer of asbestos was between two and three feet in length and the air after having traversed it no longer contained any white fumes. From the asbestos tube the air passed into a solution of clear baryta water. A precipitate was formed at once and increased in quantity the longer the current continued. “It was tested for phosphoric acid and phosphorus in general but not a trace could be detected. The current of air over the phosphorus was continued for several days in order to obtain enough of the precipitate for examination and analysis. It proved to be nothing but barium carbonate.”
“The carbon dioxide must have come from one of two sources, either from some carbonaceous substance contained in our phosphorus, or as the result of the action of ozone on the cork stoppers used to make connections. The use of rubber was avoided as far as possible, and every precaution was taken as in the earlier experiments on the carbon monoxide and ozone. It did not appear improbable therefore that the difficulty arose from the use of impure phosphorus. Phosphorus was, therefore, obtained from as many different sources as possible, and with each of these the above described experiment was repeated, using the same apparatus. In every case the precipitate of barium carbonate was obtained and as far as could be estimated in about the same quantity. Attempts were then made to purify the phosphorus. One specimen was placed in hot water under the receiver of an air pump and the air exhausted, for the purpose of recovering any gases which might be contained in the phosphorus. Other specimens were distilled in an atmosphere of pure hydrogen and the vapor condensed in cold water. No matter what process of purification had been adopted the phosphorus acted in the same way afterwards as before.”
“We then constructed an apparatus in which the gases could at no point come in contact with cork stoppers or rubber joints. This consisted of a flask of from three to four litres capacity, provided with a doubly perforated cork stopper. Through this there passed one glass tube reaching to the bottom of the flask, and another reaching only half way. Outside the flask the shorter tube was connected with the wash bottles used to purify the air from carbon dioxide, while the longer tube was bent twice at right angles, and passed through the stopper of a U tube about 8 in. high. In the flask there were placed two or three sticks of phosphorus, each three or four inches long, and enough distilled water to somewhat more than fill the neck when the flask was inverted. The U tubes were filled with moistened asbestos which had been previously ignited. There was then added some mercury, so that when the tubes were inverted in which position the entire apparatus was placed when in use the mercury covered the corks with a layer from three quarters to an inch in thickness.