VELOCITY OF IONS FROM ELECTRIC ARCS AND FROM HOT WIRES
MUCHinterest is being shown a t present con- ' ' cerning ionization of gases and electron theories of electricity. An investigation now in progress promises to throw further light on this subject, in fact to change one idea which has been held. I t has been stated by eminent authorities that in the case of discharge through gases the negative ions always go faster than t h e positive under the same conditions. The present investigation shows that this is not always the case and a brief account
... nd a brief account of it may not be amiss. The work had its origin in a n attempt to explain the phenomena of the electric arc. I t was shown in the Physical Review * that all the phenomena of the arc could be explained b y assuming, first, that the current in the arc was carried by ions, and second, that the positive ions move the more rapidly. The second part of this hypothesis did not a t first seem probable, since in all cases which had previously been investigated the negative ions had been found to move the more rapidly. Two sets of experiments were, however, given as tending to substantiate that hypothesis, but neither of them could be considered conclusive. j-More recently experiments have been performed with ions drawn out from a n arc by a charged body in the neighborhood.$ The positive ions in this case were found to have the greater velocity. Quite recently the same fact has been shown by a n application of a * Phys. Rev.,10, 151. t Since publishing the above-mentioned article I find that part of the work there described had already been described by Dewar (Chem. A7ews, 45, 37). My own work was performed without knowledge of that done by Demar, and the method used was not the same as his. The results of the two investigations agree fully. The explanation of the results beered by myself was not suggested in his article. f Phys. Rev.,12, 137. method used by Zeleny * for finding the velocity of ions produced by X-rays. These methods are entirely independent and the agreement of the results in the two cases leaves little reason to doubt the correctness of the conclusiou that the positive ions here move the more rapidly. Of course, this is not a proof that the positive ions in the a r c itself move more rapidly than the negative, but since such a n assumption would explain the phenomena of the arc and since the positive ions just outside the arc do have the greater velocity, it seems reasonable to assume that they do also within the arc. I t opens up, however, a still more interesting field of inquiry, i. e., that concerning the condition under which the positive ions show this peculiarity. The discharge from hot platinum and iron wires was accordingly investigated. I t has long been known that positive electricity escapes from hot metals easier than negative. An examinatioii of the velocity of the ions from the hot metals showed that here also the positive ions move the more rapidly. Both the methods used in the previous investigation led to the same conclusion. But in all these cases the action is complicated by the fact that both gases and solids are present. For example, in the case of discharge from hot platinum wire atoms of platinum are no doubt given off, since it is a wellknown fact that platinum wire when heated t o a white heat decreases in weight. j-It may be that because of some contact difference of potential the negative ions of the metal never escape from the metal. A comparison of positive ions of one substance with negative of another would not be of great value. One would wish to know whether the positive ions move faster than the negative ions from which they have been separated. The case of the arc is still more complicated, for many different solid and gaseous substances enter into the arc. The investigation by Arons 4 on the arc between metals in H a n d N a t different pressures show8 that both the terminals of the arc and the gases about it must be considered.