Rays of Positive Electricity and Their Application to Chemical Analyses/On the Nature of X3 the Substance Giving the 3 Line

The only known substances which could give the line with the value of mfe three times that of the hydrogen atom are :

(1) an atom of carbon charged with four units of electricity, and

(2) a molecule containing three atoms of hydrogen.

The first of these alternatives must be abandoned  for the following reasons: (1) we have seen that a line corresponding  to  multiple charge on an atom is accompanied, unless  the pressure is exceedingly low, by certain peculiarities in the line corresponding to the atom with one charge; for example, If were a line corresponding to a carbon atom with two charges, the line corresponding to the carbon atom with one would be prolonged until its extremity was only one-half the normal distance from the vertical axis; If there were a line corresponding to the carbon atom with three charges, the ordinary carbon line would be prolonged until its distance from the vertical was only one-third of the normal distance, while a carbon atom with four charges would prolong the ordinary carbon line to within one-quarter of the distance from the axis. Again the greater the charge the less the intensity, so that a line due to a quadruply charged carbon atom would be accompanied by a stronger line due to a triply charged atom, a still stronger one due to a doubly charged atom, while the normal carbon line would be the strongest of all.

Now in the case of the 3 line we do not find any of these characteristics; the carbon line is not prolonged to within one-quarter of the normal distance, and so far from the line being accompanied by a stronger line due to a doubly charged carbon atom, in many of the cases where the 3 line is strongest the line due to the doubly charged atom is not strong enough to be detected; indeed in some of these cases the 3 line is stronger than the normal carbon line.

Again since the gas giving the 3 line can be stored In the vessel A for days after the bombardment has ceased, if this line were due to carbon with four charges it must be because some carbon compound Is formed by the bombardment, which when introduced Into the discharge tube gives, when the discharge passes through it, carbon atoms with four charges. Now experiments have been made with a great variety of carbon carbons introduced directly Into the discharge tube, CH$3$, CO$4$, CO, C$2$H$2$ QH3, COCl$4$, CCI$3$, and many others, and none of these have given this line: we must therefore abandon this solution of the problem.

I find too that whenever large amounts of X$4$ are produced spectroscopic examination shows that considerable quantities of hydrogen are liberated by the bombardment; in fact the brightness in the spectroscope of the hydrogen lines in the bombardment vessel may be taken as giving a rough indication of the brightness to be expected of the X$3$ line in the positive ray photograph.

Let us next consider the connexion between the production of X$3$ and the nature of the substance bombarded by the cathode rays. We get more definite conditions for the bombarded body if we use soluble salts instead of pieces of metal or minerals. The latter may have absorbed X$3$ and contain stores of this gas in the absorbed state which are liberated when the solid is bombarded by cathode rays. If we could subject the solid before the bombardment to some process by which we could free it from absorbed gas we should expect that if the source of the X$3$ were gas absorbed by the solid, the bombardment of a substance which had been treated in this way would not give rise to any X$3$.

The most effective way of liberating the absorbed gas would seem to be to dissolve the solid in a suitable solvent and then evaporate the solution to dryness. Those salts which are soluble in water or alcohol can readily be treated in this way. I have therefore made experiments on a large number of soluble salts bombarding them before and after they have been dissolved and evaporated to dryness, and testing by the positive ray photographs the yield of X$3$ in each case. Sal-ammoniac made by allowing streams of ammonia and hydrochloric acid gas was found to give X$3$ when bombarded; in this case the possibility that X$3$ was absorbed in the salt would seem to be excluded.

I find that salts may be divided Into two classes with respect to the way in which their evolution of X$3$ is affected by solution and evaporation. One class of salts which Includes KI, Li$3$CO$2$, KCl give a very much smaller output of X$3$after this treatment than they did before; the other class which includes KOH, LiCl, LiOH, CaCl$3$ give much the same output after solution as they did before even though they are dissolved and evaporated over and over again. The salts of the first class do not contain hydrogen, while those of the second either contain hydrogen or are deliquescent and thus can absorb water from the atmosphere on their way to the bombardment chamber after evaporation. The fact that some salts continue to give supplies of X$2$ after repeated solution and evaporation shows I think that X$3$ can be manufactured from substances of definite chemical composition by bombardment with cathode rays, and the fact that such salts contain hydrogen either as part of their constitution or in water of crystallization suggests that X$3$ consists of hydrogen and is represented by the formula H$3$. The other alternative is that it is an element produced by the disintegration of some or other of the elements in the salt, but this view would not explain why its production is so closely associated with the presence of hydrogen.

One of the most convenient ways of preparing X$3$ is to bombard potash, KOH, by cathode rays. I bombarded a few grammes of potash for several months pumping off after each day's running the gases liberated by the bombardment, these consisted of H$3$. O$2$ and X$2$ and at the end of the time I could not detect any falling off in the rate of production of X$3$. By bombarding the potash, supplies of X$3$ mixed with hydrogen and oxygen were obtained and a series of experiments made with them with the object of discovering some of the properties of this gas. The method used to test for the presence of X$3$ after the mixed gases of which it was a constituent had been subjected to any treatment was to introduce a small quantity of the mixed gases into the discharge tube, take a positive ray photograph and estimate the brightness of the X$3$ line. Before such experiment the discharge tube was well washed out with oxygen and a test photograph taken to make certain that no X$3$ was In the tube before the introduction of the gas which was to be tested. One property of this gas, that of combining with mercury vapour when an electric discharge passes through a mixture of these gases, has already been mentioned. Another property was discovered accidentally: the mixed gases obtained by bombarding the potash were drawn off day by day and stored up for further tests. It was soon noticed that some of the samples kept much better than others and it seemed possible that this difference might be due to differences in the brightness of the light to which the samples had been exposed. To test this a piece of magnesium wire was burnt In front of a sample which was known to contain a considerable quantity of X$3$, with the result that the X$3$ almost disappeared. The gas exposed to the light was a mixture of hydrogen, oxygen and X$3$, if the oxygen is taken out of the mixture by absorbing it with charcoal cooled with liquid air, exposure to light produces no effect on the X$3$; the conclusion we.draw is that under the Influence of the light the X$3$ combines with oxygen. If the mixture is kept In the dark or if the oxygen Is taken out of it the X$3$ lasts for a long time, certainly for several weeks. Again If a strong spark is sent through the mixture containing oxygen so that a vigorous explosion takes place the X$3$ disappears, presumably combining with the oxygen. If the oxygen is removed the mixture of hydrogen and X$3$ will stand a good deal of sparking without any considerable diminution in the amount of X$3$.

The fact that sparking with oxygen destroys the X$3$, makes the removal of the hydrogen, which is by far the largest constituent of the mixture, a matter of considerable difificulty. The most effective way I know of increasing the proportion of X$3$ is first to remove the oxygen, then to put the mixture of H$3$ and X$2$ into a vessel to which a palladium tube is attached; when the palladium is heated to redness the hydrogen diffuses through it much more rapidly than the X$3$, though some of this gas can get through the palladium. The result is that the gas left behind in the vessel contains a much greater proportion of X$3$ than it did before. The preponderance of Hg in the original mixture is, however, so great that even by this means I have not been able to prepare any sample in which the hydrogen was not greatly in excess.

Another interesting property is that the X$3$ almost disappears when placed in a quartz tube with some copper oxide and the whole heated to a red heat.

In the absence of oxygen and copper oxide X$3$ may be heated to a high temperature without destruction. Summing up the results we see that when hydrogen is present in the substance bombarded a continuous supply of X$3$ can be obtained, while from substances which do not contain hydrogen the supply is soon exhausted. Again, under certain conditions such as exposure to bright light, vigorous sparking in the presence of oxygen, contact with glowing copper oxide, X$3$ combines with oxygen. These results seem to me to point to the conclusion that X$3$ is tri-atomic hydrogen H$3$. If this is so, its properties are very interesting. Unlike O3 its existence cannot be reconciled with the ordinary views about valency. If, however, we regard an atom of hydrogen as consisting of a positive nucleus and one negative corpuscle, it will exert forces analogous to those excited by a magnet and I can see no reason why a group of three of these arranged so that their axes form a closed ring should not form a stable arrangement.

The stability of X$3$ Is much greater than that of ozone O$3$. the latter does not persist for nearly as long as X$3$. It breaks up at a moderate temperature which would have no effect on Xj, and it disappears under a kind of sparking which would leave X$3$ undecoinposed. In fact X$3$ seems more stable than any known allotropic form of an element.

Many attempts have been made to obtain spectroscopic evidence of X$3$ by putting mixtures of this gas and hydrogen In a quartz tube and photographing the spectrum obtained when a discharge was sent through the tube, the electrodes were pieces of tin-foil placed outside the tube. No lines which could be ascribed to X$3$ were detected, the first and second spectra of hydrogen were bright, and in spite of efforts to get rid of mercury vapour the mercury lines were visible.

Bombardment by cathode rays is not the only method of obtaining X$3$. I heated by an electric current in a good vacuum a fine tantalum wire, such as are used for metallic filament lamps, until it fused and found that a considerable amount of X$3$ was given off. Some time ago I found that when the discharge from a Wehnelt cathode was sent through an exhausted tube X$3$ was liberated. I have found subsequently that It is not necessary to send the discharge through the tube, the heating of the cathode is sufficient to liberate this gas. Again if a considerable quantity of potash is placed in a vacuum and left for some time an appreciable quantity of X$3$ is liberated.